Covered Bridges

and the Birth of

American Engineering

Justine Christianson & Christopher H. Marston, Executive Editors



Historic American Engineering Record

National Park Service

Washington, D.C.

2015
This study is part of the Research, Technology and Education portion of the National 

Historic Covered Bridge Preservation (NHCBP) Program administered by the Federal 

Highway Administration. The NHCBP program includes preservation, rehabilitation and 

restoration of covered bridges that are listed or are eligible for listing on the National 

Register of Historic Places; research for better means of restoring, and protecting these 

bridges; development of educational aids; and technology transfer to disseminate 

information on covered bridges in order to preserve the Nation’s cultural heritage.

This study is conducted under a joint agreement between the Federal Highway 

Administration– Turner Fairbank Highway Research Center, and the National Park 

Service–Historic American Engineering Record (HAER).

Federal Highway Administration Program Manager–Sheila Rimal Duwadi, P.E.

HAER National Covered Bridges Recording Project Leader–Christopher H. Marston

Published in 2015 by the Historic American Engineering Record, National Park Service, Washington, D.C.

© 2015 by the Historic American Engineering Record

All rights reserved

Library of Congress Control Number: 2015955439

ISBN: 978-0-578-17106-7

Book design by Michael Bechetti, Creative Communication Services, Department of the Interior, Washington, D.C. 

Book printed by Westminster Printing, Santa Ana, Calif.

Distributed by the Historic American Engineering Record

Cover The Kidd’s Mill Bridge (1868) in Mercer County, Pennsylvania, is a early example of a truss patented by Ohioan Robert W. 

Smith, whose prefabricated wooden bridges successfully competed with iron ones during the late 1860s-early 1870s. HAER PA662-7, Jet Lowe, photographer, 2006.

Title Page Cutaway perspective view of a 3-D model of J.J. Daniels’ West Union Bridge (1876) in Parke County, Indiana, using 

data collected through Leica laser scanning. HAER IN-105, sheet 1, Jeremy Mauro, Benjamin Shakelton, Christopher H. Marston, 

delineators, 2014.
Dedicated to Eric N. DeLony

Eric DeLony’s love of historic bridges, such as the Thomas Viaduct (1835) seen here,

led to many initiatives to document historic bridges around the country during his

thirty-year career at HAER from 1971-2003. Christopher H. Marston, photographer, 2012. 

Contents

Introduction and Acknowledgments 

Justine Christianson and Christopher H. Marston ..................................... 1

Portfolio of Covered Bridge Trusses Recorded by

the Historic American Engineering Record

Edited by Christopher H. Marston ................................................ 4

1. HAER and the Documentation of Covered Bridges

Richard O’Connor ........................................................... 31

2. Overview of the National Historic Covered Bridge Preservation Program

Sheila Rimal Duwadi ......................................................... 39

3. History of Covered Bridges in the United States

Lola Bennett ............................................................... 49

4. Engineering Design of Covered Bridges

Dario Gasparini, Rachel Sangree, and Jim Barker;

edited by David A. Simmons and Michael R. Harrison .................................. 77

5. The Development of the American Truss

Dario Gasparini, Rachel Sangree, and Matthew Reckard;

edited by David A. Simmons ................................................... 117

6. Builders and Practices

Joseph D. Conwill ........................................................... 159

7. The Preservation and Future of Covered Bridges in the United States

Justine Christianson and Christopher H. Marston .................................... 185

Bibliography ........................................................... 205 

Author Biographies .................................................... 213

Appendix: Covered Bridges Documented by HABS/HAER ........................... 217

Index .................................................................. 229

1

Introduction and

Acknowledgments

by Justine Christianson and Christopher H. Marston

A covered bridge in a bucolic setting has become a quintessentially American image, one 

meant to evoke a pastoral vision of nineteenth-century America. Underneath the housing 

of a covered bridge, however, is a more complex story. By manipulating a basic form—the 

triangle—civil engineers and builders developed truss types suitable for different topographies, spans, 

and modes of transportation. These wood trusses were later adapted for use with metal, which generally 

usurped wood bridge construction in the first part of the twentieth century. This book examines the 

development of wood trusses and covered bridge construction, explores the function of trusses in 

covered bridges, and looks at the preservation and future of these distinctly American bridges. 

The Historic American Engineering Record’s multi-year, multi-faceted National Covered Bridges 

Recording Project extended from 2002 to 2015 thanks to funding from the Federal Highway 

Administration’s National Historic Covered Bridge Preservation (NHCBP) Program. Eric DeLony, 

former chief of the Historic American Engineering Record (HAER), developed this comprehensive 

documentation project. Sheila Rimal Duwadi and her predecessor, Steve Ernst, of the Federal 

Highway Administration (FHWA), ably administered the funding. At the core of the project has 

been the documentation of covered bridges across the United States. A total of eighty covered bridges 

have been documented with large-format photographs and written historical reports. Measured 

drawings have been completed on thirty-one bridges, and engineering analyses of several truss types 

were performed on sixteen structures. From this comprehensive examination of covered bridges, 

it has been possible to develop both historical narratives and analyses of wood-truss design and 

development in the United States.

Such an ambitious project would not have been possible without the aid of the numerous scholars, 

students, professionals, and community members who contributed in myriad ways. First, thanks are 

due to the advisory group of covered bridge experts, engineers, and Federal Highway Administration 

and National Park Service personnel who met in Washington, D.C., in February 2002 to develop the 

project. Led by Eric DeLony, the participants included Jim Barker, John Bowie, Steve Buonopane, 

Ben Brungraber, Joseph Conwill, Neal Daniels, Steve Ernst, David Fischetti, Dario Gasparini, Judy 

Hayward, Nick Jones, Emory Kemp, Chris Leedham, Jan Lewandoski, Christopher H. Marston, Tom 

McGrath, Richard O’Connor, Phil Pierce, John Sprinkle, Laurie Trippett, Tom Visser, Tom Vitanza, 

and David Wright. Their discussions helped set the course for the documentation that informs this book.

Introduction and Acknowledgments
2

Scores of students and preservation professionals have participated in the documentation of covered 

bridges. Field teams spent days climbing in and around the trusses in all kinds of weather and under 

various conditions, obtaining measurements for use in the numerous drawings produced for HAER 

and as part of the preparation of descriptions and analyses for the written historical reports and 

engineering reports. Special thanks go to all who provided access to bridges and research facilities 

across the country to facilitate the documentation.

HAER summer field team members (2002–2014) included: Lola Bennett, Mark M. Brown, Kimberly 

Clauer, Vuong Dang, Sarah Dangelas, Alicia Decatur, William Dickinson, Pavel Gorokhov, Dave 

Groff, Amy James, Dylan Lamar, Douglas Parker, Megan Reese, Bradley Rowley, Hummam 

Salih, and Benjamin Shakelton. Several field team members were interns from the International 

Council on Monuments and Sites (ICOMOS) U.S. summer exchange program, which provided a 

remarkable cross-cultural experience: Csaba Bartha, Silvia Nadine Bauer, Dr. Philip S. C. Caston, 

Charu Chaudhry, Francesca da Porto, Magdalena Karakova, Arnold Kriesel, Francesco Lanza, 

Dorottya Makay, Michiko Tanaka, and Shweta Vardia.

Dr. Dario Gasparini, Dr. Stephen Buonopane, Professor John Ochsendorf, Dr. Rachel Sangree, 

Dr. Benjamin Schafer, and Justin Spivey served as engineering consultants to the field teams and 

produced several engineering reports. In addition, the following academic and professional partners 

also produced documentation: David Ames, University of Delaware; Richard K. Anderson, Jr., 

Cultural Resource Documentation Services; Jim Barker, Dave Millen, Matthew Reckard, Ken 

Sutton, Paula Sutton, and Jingyuan Zhou, J.A. Barker Engineering, Inc.; Jim Berilla, Neal Harnar, 

and Kamil Nizamiev, Case Western Reserve University; Hannah Blum, Johns Hopkins University; 

Randy Bosnel, Smith Neubecker & Associates; Brad Dameron, Ball State University; and Sarah 

Ebright and Alex Smith, Bucknell University. 

Many current and former HAER staff members worked on this project, including Thomas 

Behrens, Naomi Hernandez, J. Lawrence Lee, Dana Lockett, Anne E. Kidd, Jet Lowe, Anne 

Mason, Kristen O’Connell, Richard O’Connor, James Rosenthal, and Jeremy Mauro. The late Jack 

Boucher photographed several covered bridges for HABS and HAER over his sixty-year career. The 

National Park Service’s Cultural Resources Geographic Information Systems facility staff (John 

Knoerl, Deidre McCarthy, James Stein, and Matt Stutts) provided invaluable assistance in mapping 

extant covered bridges. NPS’s Historic Preservation Training Center (HPTC) has been a NHCBP 

program partner since 2002. Tom McGrath, former superintendent of HPTC, served as chair of 

the First National Covered Bridge Conference in 2003. Tom Vitanza served as lead editor of the 

forthcoming Guidelines for Rehabilitating Historic Covered Bridges, a collaborative effort of the 

NPS and FHWA, which will provide guidance for rehabilitating covered bridges to the Secretary 

of the Interior’s Standards for Rehabilitating Historic Properties. 

USDA Forest Service’s Forest Products Laboratory partners Mike Ritter and Karen Martinson 

set a high bar with their related research projects for the NHCBP program. Brent Phares at Iowa 

State University oversees the National Center for Wood Transportation Structures Web site (http://

www.woodcenter.org), which is the repository for the online version of the World Guide to Covered 

Bridges and the proceedings of the Second National Covered Bridge Conference. The 2013 Dayton 

Covered Bridges and the Birth of American Engineering
3

conference served as a celebration of the NHCBP program as well as a ten-year update on the state 

of covered bridge preservation, both nationally and internationally. The following helped make the 

event a great success: Christopher H. Marston (conference chair), David A. Simmons (paper chair), 

Sheila Duwadi, Dario Gasparini, Dave Kirwin, Jane Lightner, Doug Miller, Terry Miller, Dorothy 

Printup, Steve Simmons, and Bill Vermes. 

A significant debt of gratitude is also owed to several key people. Lola Bennett and Joseph Conwill 

have been involved in the HAER National Covered Bridges Recording Project since its inception 

and have graciously answered a multitude of questions about covered bridges throughout the 

years with incomparable patience. In addition to writing fifty-eight HAER historical reports, 

Lola also wrote five nominations and the comprehensive covered bridges context study for the 

National Historic Landmarks Program and served as the initial curator of the traveling exhibit 

Covered Bridges: Spanning the American Landscape. The National Society for the Preservation 

of Covered Bridges and its late president, David Wright, provided a wealth of information for 

chapter 7, and Bill Caswell assisted with providing images from the society’s extensive archives. 

Bridgewright Timothy Andrews provided valuable information on historic construction methods. 

Michael R. Harrison and David A. Simmons brought their considerable knowledge and editing 

skills to improving the manuscript. 

The majority of images come from the Historic American Buildings Survey and the Historic 

American Engineering Record collections at the Library of Congress. We owe a debt to Anne Mason, 

collections manager, HABS/HAER/HALS, and to Ford Peatross and his staff at the Library of 

Congress for maintaining this remarkable collection.

The other images used in this book come from many collections, both institutional and personal. 

We would like to thank the following for their assistance: Ron Anthony, Anthony & Associates, Inc.; 

Pamalla Anderson, Southern Methodist University; Brian K. Brashaw, University of Minnesota–

Duluth; Aimee Brooks, Columbus Museum; Bill Caswell and Joseph Conwill, National Society 

for the Preservation of Covered Bridges; Bill Cockrell, Oregon Covered Bridge Society; Johanna 

Descher, École Nationale des Ponts et Chaussées; Paul Espinosa, George Peabody Library, The 

Sheridan Libraries, Johns Hopkins University; James Garvin; Hopkinton (New Hampshire) 

Historical Society; Dario Gasparini and Gerhard Welsch, Case Western Reserve University; Pavel 

Gorokhov; Jean-Pierre Jerome, Parks Canada; Hillary S. Kativa, Historical Society of Pennsylvania; 

Matthew Kierstead; Tevis Kimball, Jones Library, Inc.; Katherine Krile, Smithsonian Institution 

Traveling Exhibition Service; Francesco Lanza; Athena LaTocha, National Academy Museum; Jane 

Lightner, Preble County Historical Society; Miriam Wood Collection; Jack Peters; Lizanne Reger, 

Smithsonian Institution’s National Portrait Gallery; David A. Simmons, Ohio History Connection; 

Jim Smedley, Maryland Covered Bridges Web site and Theodore Burr Covered Bridge Society; 

Will Truax; Tom Vitanza; Robert M. Vogel; and Thomas E. Walczak, Theodore Burr Covered 

Bridge Society. 

Finally, we greatly appreciate all the covered bridge enthusiasts, historical societies, preservationists, 

engineers, builders, craftsman, and other professionals who work every day to preserve and save 

covered bridges for future generations.

Introduction and Acknowledgments
Portfolio of Covered Bridge 

Trusses Recorded by the Historic 

American Engineering Record

Edited by Christopher H. Marston

This section previews the variety of wooden truss types typically found in covered bridges from 

the HAER Collection. Many other HABS and HAER images are used throughout the book to 

illustrate the many aspects of covered bridge engineering.

Figure 0.1 Diagram created by Lola Bennett, Thomas Behrens, Charu Chaudhry, and Christopher H. Marston, 2006.

4 Covered Bridges and the Birth of American Engineering
5

Truss Types found in Covered Bridges

Portfolio of Covered Bridge Trusses Recorded by the Historic American Engineering Record

Figure 0.2 Diagram by Thomas Behrens, Lola Bennett, Pavel Gorokhov, and Christopher H. Marston, 2006, 2014. 
6

Ancient Truss Types

Kingpost Truss

Figure 0.3 Pine Brook Bridge (1872) in Washington County, Vermont, is a 48-foot-long kingpost-truss bridge, rehabilitated by 

Milton Graton in 1977. The kingpost truss, a simple truss design commonly used for roof framing for centuries, was a common

truss type sufficient for modest spans. There are only about twenty historic examples of kingpost-truss covered bridges remaining

in the United States. HAER VT-37-8, Jet Lowe, photographer, 2006.

Covered Bridges and the Birth of American Engineering
7

Figure 0.4 Located in Douglas County, Oregon, Neal Lane Bridge (1939), a 42-foot-long kingpost-truss bridge, features paired 

1 3/4-inch-diameter iron rods as its center posts. It is the only kingpost design surviving of the many wood trusses built from

standard plans by the Oregon State Highway Commission. HAER OR-126-5, Jet Lowe, photographer, 2004.

Queenpost Truss

Figure 0.5 The Flint Bridge (1874) in scenic Orange County, Vermont, is a queenpost-truss bridge restored by Milton Graton in 1969. 

HAER VT-29-5, Jet Lowe, photographer, 2003.

Portfolio of Covered Bridge Trusses Recorded by the Historic American Engineering Record
8

Multiple-Kingpost Truss

Figure 0.6 A variant of the multiple kingpost with later modifications, Taftsville Bridge (1836) displays aspects of an early craftsman 

tradition such as the multiple braces at the end of the trusses as seen in the foreground. HAER documented the Windsor County, 

Vermont, bridge prior to its rehabilitation after Hurricane Irene. HAER VT-30-8, Jet Lowe, photographer, 2003.

Figure 0.7 The multiple-kingpost Humpback Bridge 

(1857) in Alleghany County, Virginia, displays marked 

camber. This National Historic Landmark is the last 

surviving original structure on the James River and 

Kanawha Turnpike, a major thoroughfare across the 

Appalachian Mountains. HAER VA-1-15, Jack Boucher, 

photographer, 1971. 

Covered Bridges and the Birth of American Engineering
9

Figure 0.8 Kenyon (Blacksmith Shop) Bridge, a 96-foot-long multiple-kingpost truss in Sullivan County, New Hampshire, was 

constructed by James Tasker in 1882. HAER NH-40-4, Jet Lowe, photographer, 2003.

Portfolio of Covered Bridge Trusses Recorded by the Historic American Engineering Record
10

Major Developmental Truss Types

Burr-Arch Truss

Figure 0.9 The Village Bridge (1833) in Washington County, Vermont, is a Burr-arch truss bridge noted for its hand-tooled knee braces 

added by Milton Graton during repairs in the early 1970s. The hand-tooled knee braces replaced steel sway braces added during the 

mid-twentieth century. HAER VT-34-4, Jet Lowe, photographer, 2004.

Covered Bridges and the Birth of American Engineering
11

Figure 0.10 The Burr-arch truss on the Duck Creek Aqueduct (1846) in Franklin County, Indiana, features flared posts and is the sole 

remaining covered wood aqueduct in the country. It was designated a National Historic Landmark in 2014. HAER IN-108-2, James 

Rosenthal, photographer, 2004. 

Figure 0.11 Barrackville Bridge (1853) in Marion County, West Virginia, is a 131-foot span Burr-arch truss bridge. HAER documented

the bridge following rehabilitation by Emory Kemp in 1999. It is one of three extant bridges completed by West Virginia bridge builder

Lemuel Chenoweth. HAER WV-8-23, Jet Lowe, photographer, 2002. 

Portfolio of Covered Bridge Trusses Recorded by the Historic American Engineering Record
12

Figure 0.12 Built by Indiana master builder J. J. Daniels, Jackson Bridge (1861) in Parke County, Indiana, is a Burr-arch truss with 

paired diagonals, posts, and arches. With a span of 207 feet, the Jackson Bridge is the nation’s longest single-span wood truss that 

still carries vehicular traffic. HAER IN-48-7, James Rosenthal, photographer, 2004. 

Figure 0.13 Pine Grove Bridge (1884) between Chester and Lancaster Counties, Pennsylvania, is one of eleven bridges by 

Elias McMellen that still stand. Although it has been rehabilitated, it still exhibits some of the finest examples of Burr-arch truss 

framing. HAER PA-586-7, Jet Lowe, photographer, 2002. 

Covered Bridges and the Birth of American Engineering
13

Town Lattices

Figure 0.14 Built in 1829, the Bath-Haverhill Bridge in Grafton County, New Hampshire, is the oldest existing Town lattice bridge in the 

country. The laminated arches were added in 1922 to increase load capacity. HAER NH-33-14, Jet Lowe, photographer, 2003.

Figure 0.15 The Beaverkill Bridge (1865) is distinctive for its fan-like radiating planks at the ends of the lattice trusses. Carpenter 

John Davidson built this regional variation of the Town lattice in Sullivan County, New York, where two other examples survive 

from the 1860s. HAER NY-329-5, Jet Lowe, photographer, 2003. 

Portfolio of Covered Bridge Trusses Recorded by the Historic American Engineering Record
14

Figure 0.16 The Town lattice on the 110-foot span Holliwell Bridge (1880) is braced by a pair of queenpost trusses. It was 

constructed by Harvey P. Jones and George K. Foster, who together built at least five covered bridges in Madison County, Iowa. 

HAER IA-64-22, Jet Lowe, photographer, 2004. 

Figure 0.17 One of the bridges of Madison County, the Roseman Bridge (1883) is a Town lattice truss bridge with auxiliary 

queenpost trusses. HAER IA-95-6, Jet Lowe, photographer, 2004. 

Covered Bridges and the Birth of American Engineering
15

Figure 0.18 The Cornish-Windsor Bridge (1866) across the Connecticut River between Sullivan County, New Hampshire, and Windsor 

County, Vermont, is a notched Town lattice truss built by James Tasker and Bela Fletcher. With two spans of over 200 feet each, it is one 

of the longest historic covered bridges in the country. HAER NH-8-10, Jet Lowe, photographer, 1984. 

Figure 0.19 Watson Mill Bridge (1885) in Madison County, Georgia, is one of the extant covered bridges by Washington W. King, eldest 

son of Horace King, a freed slave who became a prolific bridge builder in the South. HAER GA-140-13, Jet Lowe, photographer, 2004.

Portfolio of Covered Bridge Trusses Recorded by the Historic American Engineering Record
16

Figure 0.20 The two-span, double-web Town lattice Contoocook Railroad Bridge (1889), which spans the Contoocook River

in Merrimack County, New Hampshire, was built under the supervision of J. P. Snow of the Boston and Maine Railroad.

HAER NH-38-9, Jet Lowe, photographer, 2003.

Figure 0.21 The 320-foot-long, three-span Swann Bridge (1933) features upper lateral bracing in a lattice web above its Town lattice 

trusses. One of three surviving wood bridges built in Blount County, Alabama, during the 1930s, it represents one of the last regions 

of covered bridge construction in the country. HAER AL-201-10, Jet Lowe, photographer, 2002.

Covered Bridges and the Birth of American Engineering
17

Figure 0.22 The interior view of Milton and Arnold Graton’s Hall Bridge (1982) in Windham County, Vermont, showcases the 

twentieth-century craftsmen’s knowledge of traditional timber framing and detailing in constructing a modern authentic covered 

bridge. HAER VT-40-11, Jet Lowe, photographer, 2009.

Long Truss

Figure 0.23 To span the Schoharie River, Nichols 

Powers used a double-barrel Long truss with arch

for the Blenheim Bridge (1855) in Schoharie County, 

New York. In 1964, it was the first covered bridge

to be designated as a National Historic Landmark.

The bridge was destroyed by flooding in 2011. 

HAER NY-331-9, Jet Lowe, photographer, 2004.

Portfolio of Covered Bridge Trusses Recorded by the Historic American Engineering Record
18

Figure 0.24 The Eldean Bridge (1860) in Miami County, Ohio, is one of the few remaining Long trusses that still retain their 

adjustable wooden wedges at the counterbrace panel points for prestressing. The designer of the truss, Col. Stephen Long, is 

credited with introducing mathematical theory to American bridge design. HAER OH-122-10, Jet Lowe, photographer, 2002.

Howe Truss

Figure 0.25 A Howe truss with arch carries the 233-foot span of the Bridgeport Bridge (1862) in Nevada County, California, built 

during the Comstock Lode Gold Rush by the Virginia City Turnpike Company. Massachusetts millwright William Howe introduced 

iron tension members into American bridge trusses. HAER CA-41-9 (CT), Jet Lowe, photographer, 1984.

Covered Bridges and the Birth of American Engineering
19

Figure 0.26 Knight’s Ferry Bridge (1863) in Stanislaus County, California, is a 379-foot-long, four-span Howe truss built as a major 

crossing on the Stockton to Sonora Road. Its high integrity as one of the best remaining examples of a wood and iron Howe truss 

contributed to its designation as a National Historic Landmark in 2012. HAER CA-314-8, Jet Lowe, photographer, 2004.

Figure 0.27 The 154-foot-long Howe truss Doe River Bridge (1884) in Carter County, Tennessee, is covered by a hip roof, a feature 

common in Europe but rarely found on American covered bridges. HAER TN-41-14 (CT), Jet Lowe, photographer, 2002.

Portfolio of Covered Bridge Trusses Recorded by the Historic American Engineering Record
20

Figure 0.28 Joseph Britton’s Pine Bluff Bridge (1886) is one of several Howe trusses built by Britton and his sons in

Putnam County, Indiana. HAER IN-103-4, James Rosenthal, photographer, 2004. 

Figure 0.29 Built by the Rutland Railroad in 1897, the 94-foot Howe truss Shoreham Railroad Bridge is now a feature on a 

picturesque recreational trail in Addison County, Vermont. HAER VT-32-9 (CT), Jet Lowe, photographer, 2003.

Covered Bridges and the Birth of American Engineering
21

Figure 0.30 Clark’s Railroad Bridge (1904) in Grafton 

County, New Hampshire, which was originally located 

upstate in Coos County on an important link on 

the granite-hauling Barre Branch Railroad, features 

substantial Howe trusses. Today it remains active 

on the steam excursion line at Clark’s Trading Post. 

HAER NH-39-8, Jet Lowe, photographer, 2003.

Figure 0.31 The 36-foot-long Snyder Brook Bridge (1918) in Coos County, New Hampshire, is a rare surviving Howe boxed

pony truss (with supplemental outriggers), a once common bridge type built for short spans by the Boston and Maine Railroad. 

HAER NH-49-4, Jet Lowe, photographer, 2009.

Portfolio of Covered Bridge Trusses Recorded by the Historic American Engineering Record
22

Figure 0.32 Larwood Bridge (1941) was one of several covered bridges built by the Linn County, Oregon, Engineering Department 

from 1920 through the 1940s from a standard Howe plan. The open-sided housing used throughout Linn County provided 

increased visibility and reduced wind resistance. HAER OR-124-25, Jet Lowe, photographer, 2004.

Figure 0.33 The Office Bridge (1944) in Lane County, Oregon, features a 180-foot-long Howe truss with paired braces and single 

counters measuring 14 inches x 16 inches. The massive bridge carried logging truck traffic for the Westfir lumber mill until the 

plant closed in 1977. HAER OR-125-6, Jet Lowe, photographer, 2004. 

Covered Bridges and the Birth of American Engineering
23

Pratt Truss

Figure 0.34 Although burned by arsonists in 1980, the Sulphite Railroad Bridge (1896) in Merrimack County, New Hampshire, 

survives as an example of a wood and iron Pratt deck truss. Patented by Thomas and Caleb Pratt in 1844, the Pratt truss reversed 

the configuration of the Howe truss, placing the short web members in compression and the long web members in tension, which 

reduced the danger of structural failure through buckling. Few timber Pratt-truss bridges were built, but the type was successfully 

adapted to iron and steel. By the late nineteenth century, the all-metal Pratt truss was the standard American truss for moderate 

railroad and highway spans. HAER NH-36-7, Jet Lowe, photographer, 2003. 

Portfolio of Covered Bridge Trusses Recorded by the Historic American Engineering Record
24

Regional Truss Types

Figure 0.35 This end panel of Kidd’s Mill Bridge (1868) in Mercer County, Pennsylvania, shows the extra, steeply inclined 

compression brace common to trusses patented by Robert W. Smith, who successfully introduced industrial processes into 

covered bridge construction through his two Ohio companies. HAER PA-622-5, Jet Lowe, photographer, 2006.

Covered Bridges and the Birth of American Engineering
25

Figure 0.36 The Powder Works Bridge (1872)

in Santa Cruz County, California, is a triple-web 

Smith truss built by William Gorrill’s Pacific Bridge 

Company, which introduced the Smith patent to the 

northwestern part of the country and built several 

wooden bridges in California and Oregon in the 1870s. 

HAER CA-313-9, Jet Lowe, photographer, 2004. 

Figure 0.37 Sunday River Bridge (1872) in Oxford County, Maine, is a fine example of a Paddleford truss. Invented by bridge 

builder Peter Paddleford in the 1830s, the Paddleford truss dominated covered bridge construction throughout much of northern 

New England for more than half a century. Jet Lowe, HAER ME-69-1, photographer, 2003.

Portfolio of Covered Bridge Trusses Recorded by the Historic American Engineering Record
26

Minor Truss Types

Figure 0.38 Erie Railroad engineer Simeon Post’s patented truss featured parallel inclined compression and tension members. It was 

popular on railroads throughout the 1860s and 1870s. The combination wood and iron Post truss was used on the Bell’s Ford Bridge 

(1868), a road crossing over White’s River in Jackson County, Indiana. The structure’s western span collapsed in 1999; the eastern span 

collapsed in 2006. HAER IN-46, sheet 1, Matthew Reckard, Ken Sutton, and Randy Bosnel, J. A. Barker Engineering, delineators, 2004. 

Figure 0.39 Using Gen. Herman Haupt’s 1851 patent drawing in his influential book, General Theory of Bridge Construction,

Andrew Ramsour built the Bunker Hill Bridge in Catawba County, North Carolina, in 1894; it is the last surviving example of

the Haupt truss. HAER NC-46, sheet 5, Richard K. Anderson, delineator, 2004. 

Covered Bridges and the Birth of American Engineering
27

Figure 0.40 Patented by Daniel McCallum in 1851, the McCallum truss featured an arched upper chord and prestressed 

counterbraces and was used on North American railroads during the 1860s. The Powerscourt Bridge (1861), crossing the Chateauguay 

River in Huntingdon County, Quebec, is the only surviving example of this truss type. HAER NY-332-8, Jet Lowe, photographer, 2003. 

Figure 0.41 Harshman Bridge (1894) is one of seven surviving Childs trusses built by Everett Sherman in Preble County, Ohio,

in the 1880s and 1890s. Horace Childs, a nephew and agent of Stephen Long, patented the design in 1846. HAER OH-126-10,

Jet Lowe, photographer, 2004.

Portfolio of Covered Bridge Trusses Recorded by the Historic American Engineering Record
28

Figure 0.42 Pottersburg Bridge (1872) is one of five surviving Partridge trusses. A prolific builder based in Union County, Ohio, 

Reuben Partridge patented a truss design similar to the Smith truss. HAER OH-125-9, Jet Lowe, photographer, 2003.

Figure 0.43 White’s Bridge (1869) in Kent County, Michigan, was the best surviving example of this truss patented in 1857 by 

Josiah Brown before it was lost in a fire in 2013. The regional Brown truss featured paired braces and single counters notched and 

bolted at the chords. HAER MI-331-8, Jet Lowe, photographer, 2004.

Covered Bridges and the Birth of American Engineering
29

Figure 0.44 The inverted Bowstring truss on the Germantown Bridge (1865) in Montgomery County, Ohio, is a combination wood 

and iron rigid suspension truss, in which all compression members are wood and the inverted, arched iron suspension chain is in 

tension. A rare surviving example of the transitional bridge building period from wood to iron, it is an example of the early work of 

David H. Morrison, founder of the Columbia Bridge Works of Dayton, Ohio. HAER OH-87-2, Joseph Elliott, photographer, 1992.

Figure 0.45 The Bennett’s Mill Bridge (1875) in Greenup County, Kentucky, was the sole surviving historic Wheeler truss until it 

was rebuilt in 2004. Isaac Wheeler’s truss design, featuring paired tension members, double-offset compression members, and an 

intermediate chord, was briefly popular in the Sciotoville, Ohio, area from 1870 to 1875. HAER KY-49-9, Jet Lowe, photographer, 2004.

Portfolio of Covered Bridge Trusses Recorded by the Historic American Engineering Record
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Figure 0.46 The original Hancock-Greenfield Bridge in Hillsborough County, New Hampshire, was destroyed by a flood in 1936.

New Hampshire Highway Department engineer Henry B. Pratt Jr. designed a replacement covered bridge that met modern 

regulations with the use of steel timber connectors manufactured by the Timber Engineering Company (TECO), which allowed

the bridge to handle heavier loads. Constructed in 1937 by Hagan Thibodeau Construction using federal funds, this modern

TECO truss has the distinction of being the first permanent highway span in the United States to use timber connectors.

HAER NH-42-7, Jet Lowe, photographer, 2003. 

Covered Bridges and the Birth of American Engineering
Chapter 1

HAER and the Documentation 

of Covered Bridges

by Richard O’Connor

HAER and the Documentation of Covered Bridges 31

The Historic American Buildings Survey 

(HABS), established in 1933 as one of 

the federal government’s first historic 

preservation programs, began recording covered 

bridges in the 1930s, along with numerous other 

buildings and structure types. In HABS Bulletin 

No. 3, prepared under the Civil Works Program, 

Charles Peterson wrote, 

It is intended that the survey shall 

cover structures of all types, from the 

smallest utilitarian structures to the 

largest and most monumental. Barns, 

bridges, mills, toll houses, jails, and 

in short buildings of every description 

are to be included so that a complete 

picture of the culture of the time as reflected in the buildings of the period 

may be put on record.1

Documentation of American bridges by HABS 

with large-format photographs, written historical 

reports, and hand-measured drawings was more 

than a token effort. Over the next four decades, 

HABS recorded sixty-two covered bridges, 

constituting just over a third of those now part 

of the Historic American Buildings Survey / 

Historic American Engineering Record / Historic American Landscapes Survey (HABS/HAER/

HALS) Collection at the Library of Congress’s Prints and Photographs Division, a small but important 

part of the collection’s current 41,000-plus sites and structures.

Figure 1.1. In 1936, HABS documented Smith’s Bridge, a

Burr-arch truss that spanned Brandywine Creek in New Castle 

County, Delaware. HABS documentation provides a lasting 

record of the bridge, which was destroyed by arson in 1961. 

Top: 1.1a) HABS DE-1-1, W. Gould White, photographer.

Above: 1.1b) HABS DE-1, sheet 2, Frances E. Stirlith, delineator.
32 Covered Bridges and the Birth of American Engineering

The Historic American Engineering Record picked up where HABS left off. The American Society 

of Civil Engineers, along with the National Park Service and the Library of Congress, established 

the HAER program in 1969, with subsequent endorsements from four other engineering societies. 

Bridges are unquestionably the most ubiquitous historic engineering structures on the landscape, 

existing wherever roads cross streams and rivers and span valleys. From its inception, HAER made 

bridges—wood, stone, iron, steel, and concrete—a focal point for documentation. As a subset, 

covered bridges are the oldest of these, with some extant structures dating to the first half of the 

nineteenth century.

Bridges fit well with HAER’s core mission to document endangered historic engineering and industrial 

structures. Because bridges are continually exposed to the harshest natural elements, rot and rust 

tax even the most vigilant preventive maintenance programs, but it has been the unrelenting quest 

for structures that can withstand heavier loads and greater speeds that has doomed many of our 

historic bridges. Like their counterpart industrial buildings, historic bridges rarely have alternative 

uses that would convey a new lease on life. As Robert Vogel, curator emeritus of mechanical and 

Figure 1. 2 HAER documented its first covered bridge, Humpback Covered Bridge in Alleghany County, Virginia, in 1970.

So named because of its marked camber, the bridge was designated a National Historic Landmark in 2012 as the best surviving 

example of a timber multiple-kingpost truss, making it an outstanding example of nineteenth-century bridge construction.

HAER VA-1-6, Jack Boucher, photographer, 1971.
HAER and the Documentation of Covered Bridges 33

civil engineering at the Smithsonian Institution and an early contributor to the HAER program, 

wrote, “A historic bridge . . . can never be anything but that, and once it is no longer needed at a 

certain place; or cannot cope with modern traffic loadings; or has deteriorated beyond repair only 

rarely will its original owner or any organization be willing to carry the continuing maintenance 

costs for its preservation merely as a monument.”2

 The result, he notes, is that we “resort to a poor 

second course” preparing documentation that will outlive the structure, which is actually a primary 

purpose of the HABS, HAER, and HALS programs. In a striking statistic, of the sixty-two covered 

bridges documented by HABS between 1933 and 1969, thirty-six have been “lost”— destroyed or 

demolished by the forces of nature and man.

HAER, like its counterpart HABS decades earlier, developed systematic, methodological approaches 

to understanding the universe of historic engineering structures and determining which among 

those warranted more in-depth documentation. First and foremost was the inventory that located 

and identified engineering sites and structures in a given geographic area, evaluated their integrity 

and historical value, and established a need for further recording or a context for the nomination 

of similar resources to the National Register of Historic Places. The programs produced dozens 

of state and regional inventories in the 1970s and 1980s, starting with the HABS-sponsored New 

England Textile Mill Survey in 1968 and the first HAER study the following year, A Report of 

the Mohawk-Hudson Area Survey. The most recent of the inventories covered nine central and 

western Pennsylvania counties in the late 1980s and early 1990s.3

 HAER also worked with officials 

from state departments of transportation over three decades to develop extensive state bridge 

surveys, starting with Virginia in 1970.4

 A multi-year partnership between the Federal Highway 

Administration (FHWA) and the National Park Service (NPS) resulted in the documentation of 

hundreds of bridges in nearly fifty national parks in HAER’s National Park Service Park Roads 

and Bridges Project from 1988 to 2002.5

Inventory and survey underpinned HAER’s participation in the FHWA’s National Historic Covered 

Bridge Preservation (NHCBP) Program. Fortunately, the National Society for the Preservation of 

Covered Bridges, a group of covered bridge experts and advocates, has published and updated its 

World Guide to Covered Bridges since 1956. The World Guide provides basic location, age, and 

dimensional data on the 800 or so known covered bridges in the United States, from which HAER 

developed a targeted, comprehensive documentation and study plan for its National Covered 

Bridges Recording Project. In February 2002, HAER convened a planning meeting of twenty-three 

preservation engineers and architects, timber framers, historians, transportation and preservation 

officials, and other experts in the field to develop a list of the most historically significant covered 

bridges in the United States. Several of these specialists consulted with HAER for the duration of 

the project. From the list they developed, HAER has selected and documented in greater detail 

eighty covered bridges considered by meeting participants to be the most significant.

In addition to the planning meeting and HAER documentation, other components of HAER’s 

work, done in conjunction with the NHCBP program, have built upon and expanded HAER’s 

traditional documentation, contributing in a variety of ways to the NHCBP program’s preservation 

goals. Typical, comprehensive HAER documentation consists of measured and interpretive 

drawings, large-format photographs, and historical reports that are generally a combination of 
34 Covered Bridges and the Birth of American Engineering

description and narrative. For the NHCBP program, HAER has worked with professional engineers, 

engineering students, and several universities (Case Western Reserve, Johns Hopkins, Bucknell, 

and Massachusetts Institute of Technology) to develop engineering analyses of a variety of covered 

bridge truss systems, including the Burr, Town, Long, Howe, multiple-kingpost, queenpost, Pratt, 

Childs, and Smith. These studies (on sixteen bridges) have subjected historical structures to modern 

engineering testing techniques to reveal the ways they behave under load and to answer other, more 

specific, questions.

Figure 1. 3 An essential component of the NHCBP program has been HAER documentation undertaken by teams of HAER staff 

members, students and professionals, as in this field team on site at Powerscourt Bridge (1861) in Huntingdon County, Quebec, in 

2003. Top: 1.3a) From left to right: Jean-Pierre Jerome and Christian Ouimet of Heritage Conservation Services, Parks Canada; Naomi 

Hernandez, Thomas Behrens, Lola Bennett, Dana Lockett, and Christopher Marston, HAER staff members. Courtesy of Jean-Pierre 

Jerome, 2003. Above: 1.3b) HAER NY-332, sheet 4, Thomas Behrens, delineator, 2003.
HAER and the Documentation of Covered Bridges 35

Figure 1. 4 The Duck Creek Aqueduct (1846) in Franklin County, Indiana, with its Burr-arch truss exemplifies how covered

bridge technology was adapted to a variety of transportation systems in the nineteenth century. The Secretary of the Interior 

designated the aqueduct as a National Historic Landmark in 2014. Top: 1.4a) HAER IN-108-4, James Rosenthal, photographer, 2004.

Above: 1.4b) HAER IN-108, sheet 6, Pavel Gorokhov, delineator, 2012.
36 Covered Bridges and the Birth of American Engineering

As part of the NHCBP program work plan, HAER coordinated and undertook the preparation 

of a National Historic Landmark (NHL) theme study and subsequent nominations for covered 

bridges. Theme studies assess the national significance of groups of resources and are the first step 

in the development of NHL nominations, the highest official recognition of historic properties 

designated by the Secretary of the Interior. In particular, theme studies provide the broadest possible 

context for assessing the significance of individual resources against the backdrop of all other similar 

resources. The World Guide, the experts’ workshop, and detailed HAER documentation provided 

the information necessary to develop the theme study and individual nominations. Five bridge 

nominations have successfully completed the formal process, resulting in all five bridges being named 

National Historic Landmarks: Knight’s Ferry Bridge, an 1863 Howe truss in Stanislaus County, 

California; the 1857 Humpback Bridge in Alleghany County, Virginia, the best surviving example 

of a timber, multiple-kingpost truss; Brown Bridge, an 1880 Town lattice truss in Rutland County, 

Vermont, and the best surviving example of the work of Nichols Powers; the 1846 Duck Creek 

Aqueduct in Metamora, Indiana, the only surviving covered wood aqueduct in the United States; 

and the California Powder Works Bridge, an 1872 Smith truss in Santa Cruz County, California.

Several partnerships have extended the programs’ reach. The NPS’s Historic Preservation Training 

Center (HPTC) took the lead in convening the First National Covered Bridge Conference, a 

“best practices” workshop in Burlington, Vermont, in June 2003. This event brought together over two 

hundred engineers, contractors, craftspeople, highway administrators, and covered bridge preservation 

organizations to make formal presentations and exchange knowledge of “state of the art” covered 

bridge preservation, repair, and maintenance techniques. In addition to accomplishing these goals, the 

Burlington conference also resulted in the ratification of the “Burlington Charter for the Preservation 

of Historic Covered Bridges,” a set of goals “for insuring the long term safeguarding of historic covered 

bridges.”6

 HPTC is also developing the Guidelines for Rehabilitating Historic Covered Bridges to 

disseminate information concerning the preservation and maintenance of covered bridges according 

to the Secretary of the Interior’s Standards for the Treatment of Historic Properties. In partnership 

with the Smithsonian Institution Traveling Exhibition Service (SITES), HAER mounted Covered 

Bridges: Spanning the American 

Landscape, designed to heighten the 

public’s awareness of covered bridges 

and to educate people about their 

history, their engineering features, 

and the threats to their existence. The 

exhibition travelled continuously for 

more than three years to numerous 

locations across the country.7

One vital component of the project 

from its onset has been an update of 

the World Guide. Building on over a 

half century of dedicated compiling, 

updating, and publishing by the 

Figure 1. 5 Covered Bridges: Spanning the American Landscape traveled around 

the country from 2006 to 2009. The opening panel is shown here at the Altoona 

Heritage Discovery Center in Pennsylvania. Courtesy of Smithsonian Institution 

Traveling Exhibition Service, 2009. 
HAER and the Documentation of Covered Bridges 37

National Society for the Preservation of Covered Bridges and a number of individuals, the National Park 

Service’s Cultural Resources Geographic Information Systems (CRGIS) facility created a database and 

Web application that translates the paper-based World Guide into a searchable and illustrated digital 

inventory of covered bridges. Users can search for bridges by name, location, year built, World Guide

number, and even the type of truss used. In addition to the attribute data one would find within the World 

Guide for a selected bridge, the application also displays interactive Google maps for locations of existing 

bridges, geo-tagged photographs of the bridge and/or its surroundings via the Panoramio photo-sharing 

service, interactive Google Street Views (when available), and a selection of statistical charts generated 

on the fly based upon user inputs. Additionally, users can find connections between existing bridges and 

lost bridges based upon a shared location. A select set of known and approved bridge experts can log on to 

the site and update the database dynamically, and edits can then be quickly viewed by the general public. 

The Web site is hosted by Iowa State University’s National Center for Wood Transportation Structures 

and can be viewed at http://woodcenter.org/CoveredBridges/.

As of this writing, HAER and its partners are in the process of completing several other initiatives. 

HAER convened the Second National 

Covered Bridge Conference in Dayton, Ohio, in June 2013, ten years 

after the one held in Burlington.8

Ongoing research projects include the 

reconstruction and intensive load and 

environmental testing of a Howe pony 

truss, analyzing the performance of 

existing covered bridge floor systems, 

and load testing a full-size, half-span 

model of a Burr-arch truss.

Figure 1. 6 Participants of the Second National Covered Bridge Conference 

in Dayton in June 2013 toured the covered bridges of Preble County, Ohio. 

Courtesy of Jane Lightner, Preble County Historical Society.

A decade has passed since Eric 

DeLony, former chief of the 

HAER program and HAER’s first 

permanent staff member, convened 

the first covered bridge planning meeting in Washington, D.C. After organizing and leading 

extensive bridge documentation projects ranging from Washington State’s concrete structures to 

Chicago’s bascules to Pennsylvania’s cast- and wrought-iron bridges, DeLony ended his federal 

career working with Steve Ernst and Sheila Duwadi to formalize HAER’s participation in FHWA’s 

National Historic Covered Bridge Preservation Program. With a long track record of engineering 

documentation, a wealth of wide-ranging expertise on which to draw, and multi-year funding, 

DeLony established the HAER covered bridge agenda as a model project, cascading from a 

comprehensive inventory to thorough documentation to detailed engineering studies, all geared 

toward preservation of fragile historic engineering resources. In this business, it doesn’t get any 

better than that.
38 Covered Bridges and the Birth of American Engineering

Endnotes

1 U.S. Department of the Interior, Office of National Parks, Buildings and Reservations,

Historic American Buildings Survey, HABS Bulletin No. 3, December 20, 1933, 1.

2 Robert Vogel, ed., A Report of the Mohawk-Hudson Area Survey (Washington, D.C.: Smithsonian 

Institution Press, 1973), 1.

3 Robert Vogel, New England Textile Mill Survey: Report of the First Summer’s Work, June–September 1967

(Washington, D.C.: Smithsonian Institution Press, 1968). As part of America’s Industrial Heritage 

Project (AIHP), HAER published surveys of historic industrial and engineering sites in nine counties 

in southwest Pennsylvania, including Bedford, Blair, Cambria, Fayette, Fulton, Huntington, Indiana, 

Somerset, and Westmoreland.

4 The first covered bridge recorded by HAER was the Humpback Covered Bridge (HAER No. VA-1) in 1970.

Notable HAER bridge surveys undertaken between 1986 and 2000 include examples in Ohio, 

Wisconsin, Massachusetts, Arkansas, Oregon, Washington, Iowa, Texas, Pennsylvania, Missouri, 

Illinois, and California. 

5 A portfolio of selected drawings is found in Timothy Davis, Todd A. Croteau, and Christopher H. Marston,

America’s National Park Roads and Parkways (Baltimore: The Johns Hopkins University Press, 2004).

6 The Burlington Charter and information on the 2003 “Covered Bridge Preservation: National Best 

Practices Conference” are available at http://www.uvm.edu/coveredbridges/charter.html.

7 More information on the traveling exhibition is on SITES’s Web site,

http://www.sites.si.edu/exhibitions/exhibits/archived_exhibitions/bridges/main.htm. See also 

Christopher Marston, “ ‘Covered Bridges: Spanning the American Landscape’ Traveling Exhibit 

Debuts in Harrisburg,” Society for Industrial Archeology Newsletter 35, no. 2, (Spring 2006): 1–3.

8 The program and presentations from the Dayton conference are available at

http://www.woodcenter.org/2013-national-covered-bridge-conference/papers.cfm.
39

Overview of the National Historic Covered 

Bridge Preservation Program

by Sheila Rimal Duwadi

Overview of the National Historic Covered Bridge Preservation Program

Chapter 2
 

The Federal Highway Administration (FHWA) has been administering the National

Historic Covered Bridge Preservation (NHCBP) Program since 1998, as legislated in

highway bills starting with the Transportation Equity Act for the 21st Century (TEA-21)

and continuing through the Safe, Accountable, Flexible, Efficient Transportation Equity Act—A

Legacy for Users, or SAFETEA-LU for short. Between 2000 and 2012, the program provided

funding in two key areas: grants to preserve, rehabilitate, and restore historic covered bridges; and for

research, education, and technology transfer. During this period, over 200 historic covered bridges in

twenty-four states that are listed or have been determined eligible for listing in the National Register

of Historic Places have been saved.1 

Figure 2.1 Figure 2.1 Gilpin’s Falls Covered Bridge (1860) in Cecil County, Maryland, was in danger of collapse due to decaying

members. An award of $1,040,000 from the NHCBP program funded a sensitive rehabilitation project in 2009–2010. Left: 2.1a)

The deteriorating bridge awaiting repair. Carol M. Highsmith Archive, Library of Congress, Prints and Photographs Division,

Washington, D.C., between 1980-2006. Right: 2.1b) Stabilizing the truss during Tim Andrews’ rehabilitation. HAER MD-174-4,

David Ames, photographer, 2009. 

Research, education, and technology transfer focused on finding means and methods for repairing, 

strengthening, and preserving covered bridges; producing documentation, including educational 

videos and manuals; and offering workshops and seminars. The FHWA achieved much in this effort

through close collaboration and shared resources with the National Park Service’s Historic American

Engineering Record (HAER) and the U. S. Department of Agriculture (USDA), Forest Service’s 

Forest Products Laboratory (FPL). Countless numbers of engineers, historians, researchers, scientists,

and others have been involved in this effort. As studies are completed, they are made available at 

the National Center for Wood Transportation Structures’ Web site at www.woodcenter.org. 
40 Covered Bridges and the Birth of American Engineering

What follows is a discussion of some of the highlights of the research, education, and technology 

transfer projects. 

The Covered Bridge Manual, one of the first projects completed, serves as a guide for inspection, 

repair, rehabilitation, and restoration of historic covered bridges and provides techniques that reflect 

the latest developments in the preservation field, including both theoretical and practical aspects 

of inspection, as well as historic and traditional construction. Since the goal of most owners is to 

have their covered bridges carry modern traffic, developing a manual that illustrated the right blend 

of the new and the traditional, with guidance on how to preserve the historic integrity exhibited 

in the original architectural, structural, and material characteristics of the bridge, was necessary. 

Published in 2005, it has been a valuable resource in preserving these structures.2

If unprotected, wood can be damaged from biological activity, and many covered bridges have had 

to be repaired as a result of structural deterioration. During the period historic covered bridges were 

built, there were few chemical treatments available to prevent fungi and insects from attacking and 

colonizing the wood. While covering wood trusses with roofs and sides kept the wood dry and 

slowed the deterioration of the wood members, moisture could still migrate over time, resulting in 

suitable conditions for colonization by wood-destroying organisms. Therefore, a priority has been 

the identification of chemical preservative treatments that prevent wood deterioration while still 

being safe and acceptable to the historic preservation community.

Fire is another concern as arsonists have targeted wood covered bridges. While large dimension 

timbers have inherent fire-resistive characteristics that can eliminate the need for fire retardant 

treatments (FRTs), this is not always true of small-sized members. FRTs can add an extra layer of 

protection, allowing more response time for the authorities. However, there has been a reluctance to 

use FRTs, as older treatments were known to affect the structural properties of wood and accelerate 

the corrosion of fasteners. A new generation of products is now available that reduces these problems.

Researchers at Oregon State University and at Mississippi State University, respectively, conducted 

studies to identify and evaluate chemical preservative treatments and fire retardant treatments for use 

in covered bridges that would be effective and yet still acceptable for historic preservation purposes. 

The Guide for In-Place Treatment of Wood in Historic Covered and Modern Bridges, published in 

2012, compiles the results of these studies into a practical document.3 In addition, the Covered Bridge 

Security Manual provides cost-effective, tested systems that can be used to protect against vandalism.4

Corrosion of Fasteners in Wood Treated with Newer Wood Preservatives and Guide for Materials 

Selection and Design for Metals Used in Contact with Copper-Treated Wood report on the corrosion 

effects of newer preservatives on metals and provide references for engineers to aid in selecting treated 

wood for building projects. The publications also provide design strategies to minimize corrosion of 

metals in contact with treated wood.5 Evaluating Naturally Durable Wood Species for Repair and 

Rehabilitation of Above-Ground Components of Covered Bridges examines seven wood species for 

their durability without the use of chemical wood preservatives and provides a guide for the use of 

naturally durable wood species in the rehabilitation of covered bridges.6
Overview of the National Historic Covered Bridge Preservation Program 41

A condition assessment of a bridge is essential to determining the structure’s safety. In accordance 

with the National Bridge Inspection Standards, all bridges greater than 20 feet in length and on 

public roads are required by law to be inspected every two years. While visual inspection to determine 

condition is by far the most prevalent form of inspection for all bridge types, more advanced 

technologies continue to be developed, although these have mostly been for use in evaluating steel 

and concrete structures. The project “Advanced Field Evaluation Tools for Condition Assessment 

of Wood Members in Covered Bridges” will identify, adapt, and evaluate innovative, low-cost 

technologies bridge inspectors can use to examine wood members and more accurately determine 

the condition of a covered bridge.

In addition to damage to covered bridges caused by age, environment, arson, and increasingly heavy 

loads, natural hazards such as floods have had devastating impacts on these historic structures. As 

Hurricane Irene moved up the northeastern United States in 2011, for example, the major rainfall 

and subsequent flooding associated with the storm damaged a significant number of roadways and 

bridges in Pennsylvania, New York, Massachusetts, Vermont, and New Hampshire. Several covered 

bridges were washed away during this event. Physical and analytical tests are being conducted at 

the FHWA’s Turner-Fairbank Highway Research Center to simulate the hydraulic flows anticipated 

in similar weather events in order to develop design equations and coefficients for drag, lift, and 

overturning forces, and to develop design details to strengthen bridge members and improve the 

hydraulic safety of covered bridges.

Educational materials have been developed thanks to funding from the NHCBP program. The 

comprehensive Educational Guide on the History of Covered Bridges in the United States, developed 

by the Institute for the History of Technology and Industrial Archaeology at West Virginia 

University, was designed for use by K–12 educators teaching math, science, and American history. 

It is available both in print and online formats. The guide is divided into sections for grades K–5, 

6–9, and 9–12 and includes printable lesson plans for educators, a list of covered bridges erected in 

the United States, individual bridge histories, and a companion disk with interactive and animated 

elements for students. Graphic elements consist of images and descriptive drawings that convey 

bridge type, year built, design loads, traffic, wood species, information on the designer/builder, and 

much more.7 In another educational outreach effort, funding was provided to Indiana University 

for a documentary entitled Spanning Time: America’s Covered Bridges, which has been broadcast 

nationwide on public television.8

The program has also funded efforts by the National Park Service’s Historic American Engineering 

Record (HAER) to accurately document historic covered bridges, as described in chapter 1. Such 

documentation is essential because it creates a lasting record of structures that can be quickly 

destroyed, as in the case of the Blenheim Covered Bridge in New York, which was swept away by 

raging waters during Hurricane Irene. In addition to covered bridge documentation, HAER and the 

National Park Service’s Cultural Resources Geographic Information Systems facility have created 

an interactive Web site using data from the World Guide to Covered Bridges. This site is available 

at http://www.woodcenter.org/CoveredBridges/. 
42 Covered Bridges and the Birth of American Engineering

Figure 2.2 Hurricane Irene washed away Blenheim Bridge (1855), a National Historic Landmark, in September 2011. At 210 feet, the 

bridge had one of the longest clear spans of any surviving covered bridge and was a rare surviving double-barrel Long truss. Top: 2.2a) 

Before, HAER NY-331-3, Jet Lowe, photographer, 2004. Above: 2.2b) After, Matthew Kierstead, photographer, 2012.
Overview of the National Historic Covered Bridge Preservation Program 43

Accurately documenting a covered bridge, as done according to HAER standards, requires taking 

detailed field measurements of the bridge and its various components. The use of laser scanner 

technology to produce as-built drawings, which is less labor intensive than traditional measuring 

techniques but can produce the same level of detail, is also being investigated as part of the 

NHCBP program. Two different scanning technologies have been studied. The HAER program 

used a Leica scanner to record ten historic covered bridges as part of its surveys.9 The University of 

Minnesota–Duluth tested a FARO scanner on six Midwestern bridges and produced its findings 

in the report Use of Laser Scanning Technology to Obtain As-Built Records. When feasible, laser 

scanning technology can shorten the recording process.10

Figure 2.3 New technologies for documentation include HAER’s Leica C10 scanner and 

the FARO scanner used by the University of 

Minnesota–Duluth. Top Left: 2.3a) A Leica 

C10 scanner was used to document the West 

Union Bridge (HAER IN-105). Jeremy Mauro, 

photographer, 2013. Top Right: 2.3b) Resulting 

point cloud of West Union Bridge. Scan data 

by Jeremy Mauro, 2013. Left: 2.3c) A FARO 

scanner was used to document the Cedarburg 

Covered Bridge in Wisconsin. Brian K. Brashaw, 

photographer, 2010.
44 Covered Bridges and the Birth of American Engineering

Figure 2.4 The rehabilitation of the Long truss on the Blair Bridge (1869) in Grafton, New Hampshire, required the use of staging,

a technique discussed in the forthcoming “Guidebook for Restoring Structural Integrity of Covered Bridge Members.”

Ron Anthony of Anthony & Associates, Inc., photographer, 2012.

To educate engineering and architecture students about the structural behavior and evolution of 

wooden truss designs, Johns Hopkins University is developing educational models for four significant 

trusses—the Burr, Town, Long, and Howe. Scale plans for 100-foot trusses will allow users at a 

consortium of engineering schools to construct their own models and learn the aspects of each design.

Because historic covered bridges carried much lighter loads in the past than they do today, several 

studies have been funded to better understand the load-carrying capacities of covered bridges, to 

develop methods to strengthen members and establish more accurate rating procedures, and to 

identify ways to decrease dead load. In Strengthening Historic Covered Bridges to Carry Modern 

Traffic, West Virginia University assessed the use of fiber-reinforced polymers as a means of 

strengthening components.11 Studies still in process through the Forest Products Laboratory 

include “Improved Ratings for Covered Bridges through Load Testing,” which will develop rating 

procedures for reliably determining safe load-carrying capacity. “Improved Analytical Techniques 

for Historic Covered Bridges” will recommend improved analytical methods that have been 

validated using field load-test data. “Lightweight Floor Replacement Systems” will assess the use 

in covered bridges of floor systems that have been proven for bridge applications, and “Guidebook 

for Restoring Structural Integrity of Covered Bridge Members” will discuss the steps necessary for 

decision makers to identify effective rehabilitation techniques for restoring the structural integrity 

of covered bridge members.12

Unlike the properties of steel and concrete, engineering properties of wood can vary both within 

and between species. Additionally, wood is orthotropic, which means its material properties vary 

depending on grain direction. Therefore, the design values for wood given in specifications and 

standards are based on statistical samples with a conservative safety factor to account for the 
Overview of the National Historic Covered Bridge Preservation Program 45

variability. Often the species, sources, and grades of existing woods in historic covered bridges are 

difficult to identify, and the current practice is to assume a species and select wood values from 

existing specifications. As part of “Species Identification and Field-Grading of Woods in Covered 

Bridges,” a field manual is being developed to help determine the timber species and identify the 

grade so that engineering properties can be more reliably predicted.

Figure 2.5 FHWA funded a joint project between HAER, Case Western Reserve University, and the National Society for the 

Preservation of Covered Bridges to study the Moose Brook Bridge (1918) in Gorham, New Hampshine, a Howe truss that was a victim 

of arson in 2004. The original castings were restored, and bridgewright Tim Andrews reconstructed the salvaged trusses for testing in 

Case Western’s lab. Top 2.5a) The burned trusses sat idle for five years. HAER NH-48-3, Jet Lowe, photographer, 2009. Above 2.5b) The 

first truss assembled in the tab. Photograph courtesy Dario Gasparini, 2011.
46 Covered Bridges and the Birth of American Engineering

The timber trusses used in historic covered bridges set the stage for modern-day trusses. The bridge 

builders and engineers of the past ingeniously designed the truss and arch systems that make up 

these bridges to carry and transfer loads safely. The NHBCP program supports several pro jects 

studying these designs. William Howe’s patented truss permitted tightening of the tension rods to 

induce compression in the wood diagonals. The “Howe Truss Design and Performance” study will 

provide a better understanding of William Howe’s design by studying the Moose Brook Bridge, a 

Howe boxed pony truss, through both analytical and full-scale experimental tests. Similarly, Burrarch truss systems will be examined to develop a better understanding of the design and connection 

details of Theodore Burr’s designs. Portions of the recovered Bartonsville Covered Bridge will be 

used to study the performance of Town lattice trusses and the interaction of the lattice system in 

carrying and distributing loads in order to develop more precisely calibrated models.

Covered bridges represent the technological heritage of the United States. Developing techniques 

and methodologies that utilize the right blend of the new and the traditional and that result in 

preserving the historic integrity of the bridge, including its original architectural, structural, and 

material characteristics, has been the thrust of the National Historic Covered Bridge Preservation 

Program. In addition, disseminating knowledge about various aspects of covered bridges to all 

sectors of the American public remains a primary goal.
Endnotes

Overview of the National Historic Covered Bridge Preservation Program 47

1 Detailed lists of year by year project funding can be found on the Federal Highway Administration 

Web site, http://www.fhwa.dot.gov/bridge/covered.cfm.

2 Philip C. Pierce, Robert L. Brungraber, Abba Lichtenstein, Scott Sabol, J. J. Morrell, and S. T. Lebow, 

Covered Bridge Manual (U.S. Department of Transportation, Federal Highway Administration, 

Publication No. FHWA-HRT-04-098, April 2005). The report is available online at http://www.fhwa.

dot.gov/publications/research/infrastructure/structures/04098/04098.pdf.

3 Stan Lebow, Grant Kirker, Robert White, Terry Amburgey, H. Michael Barnes, Michael Sanders, and Jeff 

Morrell, Guide for In-Place Treatment of Wood in Historic Covered and Modern Bridges (U.S. Department 

of Agriculture, Forest Service, Forest Products Laboratory, in cooperation with the U.S. Department of 

Transportation, Federal Highway Administration, General Technical Report FPL-GTR-205, 2012). The 

report is available online at http://www.fpl.fs.fed.us/documnts/fplgtr/fpl_gtr205.pdf.

 4 Brent Phares, Terry Wipf, Ryan Sievers, and Travis Hosteng, Covered Bridge Security Manual (U.S. 

Department of Agriculture, Forest Service, Forest Products Laboratory, in cooperation with the U.S. Department 

of Transportation, Federal Highway Administration, General Technical Report FPL-GTR-223, 2012). The 

report is available online at http://www.fpl.fs.fed.us/documnts/fplgtr/fpl_gtr223.pdf. 

 5 Samuel L. Zelinka, Corrosion of Fasteners in Wood Treated with Newer Wood Preservatives (U. S. 

Department of Agriculture, Forest Service, Forest Products Laboratory, in cooperation with the 

U. S. Department of Transportation, Federal Highway Administration, General Technical Report 

FPL-GTR-220, 2013); Samuel L. Zelinka, Guide for Material Selection and Design for Metals Used 

in Contact with Copper-Treated Wood (U. S. Department of Agriculture, Forest Service, Forest 

Products Laboratory, in cooperation with the U. S. Department of Transportation, Federal Highway 

Administration, General Technical Report FPL-GTR-227, 2013). The reports are available online at 

http://www.fpl.fs.fed.us/documnts/fplgtr/fpl_gtr220.pdf and http://www.fpl.fs.fed.us/documnts/fplgtr/

fpl_gtr227.pdf, respectively.

 6 Grant T. Kirker, Carol A. Clausen, A. B. Blodgett, Stan T. Lebow, Evaluating Naturally Durable 

Wood Species for Repair and Rehabilitation of Above-Ground Components of Covered Bridges (U. S. 

Department of Agriculture, Forest Service, Forest Products Laboratory, in cooperation with the U. S. 

Department of Transportation, Federal Highway Administration, General Technical Report FPLGTR-224, 2013). The report is available online at http://www.fpl.fs.fed.us/documnts/fplgtr/fpl_gtr224.

pdf.

7 Institute for the History of Technology and Industrial Archeology, West Virginia University, 

Educational Guide on the History of Covered Bridges in the United States, available at http://www.

woodcenter.org/covered_bridges_education.

8 Spanning Time: America’s Covered Bridges, DVD (Bloomington, Ind.: WTIU, 2004). More 

information is available at http://www.indiana.edu/~radiotv/wtiu/bridges/#.

9 Jeremy Mauro, “Strategies for Documenting Covered Bridges Using 3D Laser Scanning and 3D 

Modeling,” Second National Covered Bridges Conference, Dayton, Ohio, 2013, available at http://

www.woodcenter.org/2013-national-covered-bridge-conference/papers.cfm.

10 Robert J. Ross, Brian K. Brashaw, and Samuel J. Anderson, “Use of Laser Scanning Technology 

to Obtain As-Built Records of Historic Covered Bridges” (U. S. Department of Agriculture, Forest 

Service, Forest Products Laboratory, in cooperation with the U. S. Department of Transportation, 

Federal Highway Administration, General Technical Report FPL-RP-669, 2012). The report is available 

online at http://www.fpl.fs.fed.us/documnts/fplrp/fpl_rp669.pdf.
48 Covered Bridges and the Birth of American Engineering

11 “Strengthening Historic Covered Bridges to Carry Modern Traffic,” FHWA TechBrief, FHWAHR-07-041. The brief is available online at https://www.fhwa.dot.gov/publications/research/

infrastructure/bridge/07041/07041.pdf.

12 All of these reports are still in development as of this writing. Upon completion, they should be 

available at Iowa State University’s National Center for Wood Transportation Structures’ Web site, 

http://woodcenter.org.

Endnotes
49

Chapter 3

History of Covered Bridges 

in the United States 

by Lola Bennett 

History of Covered Bridges in the United States

Figure 3.1 Charles Whitney wrote in the introduction to Rosalie Wells’s 1931 Covered Bridges in America, “The present 

generation does not. . . realize the important role which the timber bridge played in the early development of the American 

continent. But for the abundance of timber and the ingenuity of the American bridge builder, the construction of bridges 

across the many rivers would have been impossible when bridges were so much needed to carry the highways and railways 

into undeveloped country.” Fort River Bridge (1840) in Hampshire County, Massachusetts, carried vehicular traffic until it was 

lost to arson in 1962. The structure was captured around the turn of the twentieth century by renowned local author and 

photographer Clifton Johnson. Courtesy of Jones Library, Inc., Amherst, Massachusetts.

A mericans did not invent covered bridges, but they built them in unprecedented numbers as 

the nation expanded across the continent in the nineteenth century.1 In the process, they 

refined timber-truss design to a degree never seen before. While the practice of building 

framed timber bridges first occurred in Western Europe, American bridge builders quickly set the 

standard for timber-bridge construction, producing a succession of innovative designs that made 

possible the construction of sturdy and cost-effective bridges capable of spanning long distances and 

safely carrying heavy, moving loads. Concomitantly, these builders recognized the value of covering 

a timber bridge’s framework to ensure the structure’s longevity. By the end of the first quarter of 

the nineteenth century, the covered bridge was a ubiquitous part of the American landscape. At the 

height of covered bridge building, around 1870, there were well over 10,000 covered bridges in the 

United States.2
50 Covered Bridges and the Birth of American Engineering

The historic era of covered bridge building—the period when timber bridges were built because 

wood was abundant and cheap, and when practical knowledge of timber-framing techniques was 

passed down through successive generations of builders—began in the early 1800s and ended in 

the 1950s in the United States. The dates defining this era vary from region to region, but the 

practice of building covered bridges lasted about a century in most parts of the country. In the 

Mid-Atlantic region, covered bridges were built from 1805 until about 1920; in New England, 

from about 1810 until about 1910; in the Midwest, from the 1810s until the 1920s; in the South, 

from about 1820 until the 1930s; and in the Pacific Northwest, from the 1850s until the 1950s. By 

the 1950s, the economic competitiveness of timber bridges had disappeared, and the historic era of 

covered bridge building ended. While some covered bridges were built after this time—and they 

are still occasionally built today in a few scattered parts of the country—these revival-era covered 

bridges differ from their predecessors in that they are not part of the continuous building tradition 

that characterized the historic era of covered bridge construction, and the impetus behind them is 

nostalgia, rather than economy.3

Origins of the Covered Bridge

Timber bridges have been built in forested regions of the world for centuries.4 Wood is an excellent 

material for building; it is strong, relatively lightweight, and can be worked with common hand 

tools. Since most species of wood suitable for structural applications deteriorate rapidly when exposed 

to the weather, early bridge builders quickly learned the value of covering wood bridges with roofs 

and siding to protect the underlying framework. A wood bridge left uncovered may last fifteen 

years, but when properly covered and cared for, it can last indefinitely. A few covered bridges in 

Europe have survived for well over four centuries. Schlossbrücke (1514) in Zwingen, Switzerland, 

and Spreuerbrücke (1568) in Luzern, Switzerland, are two fine examples.

Carpenters in the forested regions of Europe began to refine the technology of framed timber 

bridges during the eighteenth century. Swiss brothers Johannes and Hans Ulrich Grubenmann 

built some noteworthy spans during that time, including the Schaffhausen and Wettingen 

bridges in Switzerland. European architects, scholars, and aristocrats studied these bridges, and 

descriptions and illustrations of the 

spans appeared in contemporary 

travel publications and technical 

literature. The Schaffhausen Bridge 

(1758) across the Rhine River was a 

two-span bridge of about 360 feet 

whose length was achieved by an 

intricate strut-braced beam design. 

The Wettingen Bridge (1766) 

across the Limmat River was a 

200-foot single-span structure 

and is believed to have been the 

first use of a true arch in a timber 

bridge. While the builders relied on 

empirical methods and their bridges 

Figure 3.2 A testament to the value of covering timber bridges, Hyde Hall 

Bridge (1825) in Otsego County, New York, is believed to be the oldest extant 

covered bridge in the nation. It is one of several covered bridges in the United 

States that are nearing the two-century mark. HABS NY-263-2, unknown 

photographer, ca. 1958.
History of Covered Bridges in the United States 51

were heavily built and complex structures, the Grubenmann brothers did boldly demonstrate the 

potential for long-span wood bridges, earning them international renown and lucrative contracts. 

Napoleon’s forces destroyed the Schaffhausen and Wettingen bridges in 1799, but several other 

Grubenmann covered bridges still survive in Switzerland, including Hundwilertobel (1778) at 

Hundwil and Kubelbrücke (1780) at Kubel.5

American builders were undoubtedly aware of—and perhaps inspired by—European covered 

bridges, but there is scant evidence to document a direct transfer of knowledge from Europe to 

North America; rather, it is likely that Americans independently developed the practice of covering 

wood bridges as the need for durable spans arose. Shortly after construction of long-span timber 

bridges began, the practice of covering them was rapidly adopted here.

Figure 3.3 This drawing, entitled “Plan of a 

Bridge to be Built over Schuylkill,” was published anonymously in The Columbian Magazine in 

January 1787. While this is the first published 

plan of a covered bridge, there is no record 

of one being built in the United States until 

the Schuylkill Permanent Bridge in 1805.

Early American Bridges 

Bridges were rare in colonial America. Logs, stone slabs, and, occasionally, stone arches spanned 

small streams, but larger waterways had to be crossed by ford or ferry. Overland travel was hazardous, 

slow, and uncertain, with delays and accidents common.6 A few ambitious river crossings were 

constructed as timber pile-and-beam structures, but, with few exceptions, long-span bridges were 

not built in the United States until after the Revolutionary War, when the growing volume of 

transportation and improving economic conditions justified the expenditure of material and labor.7 

This environment, coupled with a spirit of ingenuity and access to an abundant and cheap supply 

of timber, spurred the development of timber-bridge design in the United States.

Col. Enoch Hale took a bold first step in advancing American timber-bridge building in 1785 when 

he erected the nation’s first long-span framed timber bridge across the Connecticut River between 

Walpole, New Hampshire, and Bellows Falls, Vermont. This bridge was part of the overland route 

from Boston to Montreal and was heralded as a great achievement in its day. Hale’s braced beam 

bridge (as distinct from a truss bridge) was supported on rubble stone abutments and a timber pier 

rising from a small island in the middle of the river. The Massachusetts Spy stated, “Col. Enoch 

Hale hath erected a Bridge across Connecticut River, on the Great-Falls, at his own expense. This 

bridge is thought to exceed any ever built in America, in strength, elegance and publick utility.”8 

Although Colonel Hale’s bridge successfully carried traffic for a decade, its design was uniquely suited 

to its site and could not be easily replicated elsewhere. Within just a few years, more sophisticated 

techniques would be used to span America’s waterways.
52 Covered Bridges and the Birth of American Engineering

Creating structures of lengths much greater than a single log or beam was one of the initial challenges 

facing timber-bridge builders and required construction of a frame structure known as a truss. The 

truss, which utilizes the stable geometry of linked triangles to carry a load over a void, has been used 

for centuries for centering masonry arches and for constructing roofs. Introduced into European 

bridge building in the Middle Ages, the truss is the most efficient way to build long spans using 

wood. Italian architect Andrea Palladio popularized the concept of truss bridges in his influential 

treatise The Four Books of Architecture, which was first published in 1570.9

Figure 3.4 A portrait of Timothy 

Palmer was prepared and engraved by 

Louis Lement about 1804. Courtesy of 

George B. Pease Collection, National 

Society for the Preservation of 

Covered Bridges.

Born in Rowley, Massachusetts, in 1751, housewright Timothy 

Palmer is credited with making a quantum leap forward in bridge 

building by introducing long-span truss bridges to North America.10 

As a young man, he apprenticed with architect Moody Spofford, 

best known for his New England churches. In 1792, Palmer took up 

bridge building, erecting America’s first long-span truss bridge across 

the Merrimack River at Newburyport, Massachusetts.11 Containing 

over 6,000 tons of timber, the 1,030-foot-long structure had pileand-beam approaches, a draw span over the main channel, and 

two trussed arch spans, the larger of which measured 160 feet in 

length. One contemporary writer described it as follows: “The two 

large arches (one of which is superior to any thing of the kind on 

the continent) . . . appear to unite elegance, strength and firmness 

beyond the most sanguine expectation.”12 Palmer’s trusses closely resemble one of the plans published 

in Andrea Palladio’s book, which was available in the United States at the time, revealing, perhaps, 

the inspiration for the design.13 Palmer patented his truss design in 1797 and was much in demand 

as a bridge builder, erecting major timber spans across the Merrimack, Kennebec, Connecticut, 

Piscataqua, Schuylkill, Potomac, and Delaware rivers.14

America’s First Covered Bridge

In the late eighteenth century, Philadelphia was the largest and wealthiest city in the United States, but 

it had few bridges spanning its major waterways. A stone-arch bridge had carried the King’s Highway 

across Pennypack Creek for a century, but the deep and fast-flowing Schuylkill River posed a much 

greater challenge. As one nineteenth-century writer noted, “the character of this river is wild, and, in 

times of floods, rapid and formidable; and, to any structures of slight materials, ruinous and irresistible.”15 

Ferry service had been established in 1723, but it was often slowed or stopped entirely by floods or ice. 

In 1798, a group of forward-thinking citizens led by Judge Richard Peters incorporated the Schuylkill 

Permanent Bridge Company for the purpose of erecting a toll bridge over the Schuylkill River 

along the line of Market Street. The board of directors originally hired British engineer William 

Weston to build a stone bridge, but construction of the foundations proved so costly that, within a 

few months, the company was forced to consider alternative plans. Weston then designed an iron 

bridge for the Schuylkill crossing, but the directors were reluctant to attempt such a large span with 

the relatively untested material. After consulting with Timothy Palmer, at that time the nation’s 

preeminent bridge builder, the directors opted to build a timber superstructure on the foundations 

of the aborted stone-arch span.
History of Covered Bridges in the United States 53

Figure 3.5 Schuylkill Bridge, High Street, Philadelphia, engraving by William Russell Birch, ca. 1804. Completed in 1805, the Schuylkill 

Permanent Bridge is the first documented covered bridge in the United States. It stood for forty-five years until replaced in 1850. This 

image depicts the bridge prior to being covered, with the completed structure shown in the inset. Courtesy of Library of Congress, 

Prints and Photographs Division, Washington, D.C.

In the spring of 1804, Timothy Palmer and his assistant Samuel Carr traveled to Philadelphia to erect 

the bridge superstructure. Over the next few months, a 195-foot trussed arch center span flanked 

by two 150-foot trussed arch spans rose from the foundations. Opened to traffic on January 1, 

1805, the Schuylkill Permanent Bridge was heralded as an engineering masterpiece and “an honour 

to its inventor for its originality of architecture, and its excellence of mechanism.”16 Due to the 

extraordinarily high cost of construction—$300,000—the board of directors corresponded with 

Palmer about the possibility of covering the bridge to protect their investment from the weather. 

In his reply, Palmer affirmed the board’s decision with this statement:

I am an advocate for weather boarding and roofing, although there are some that say I argue 

much against my own interest. . . . It is sincerely my opinion that the Schuylkill bridge will last 

thirty and perhaps forty years, if well covered. . . . I think it would be sporting with property 

to suffer this beautiful piece of architecture . . . which has been built at so great expense and 

danger, to fall into ruins in 10 or 12 years! 17

The company directors hired Philadelphia architect Adam Traquair to design the covering of the bridge 

and carpenter Owen Biddle to execute it, stating that the housing “compelled ornament, and some 

elegance of design, lest it should disgrace the environs of a great City.”18 In addition to its numerous 

architectural embellishments, including statues by sculptor William Rush, the structure was given 
54 Covered Bridges and the Birth of American Engineering

two coats of ornamental stone plaster and sprinkled with stone dust to resemble a stone bridge. The 

Schuylkill Permanent Bridge had become the first documented covered bridge in North America. 

Speaking for the board of directors, Judge Peters expressed the hope that the Schuylkill Permanent 

Bridge would serve as an example “in all pontifical wooden structures of magnitude, hereafter.”19

Figure 3.6 Upper Ferry Bridge over the Schuylkill, watercolor by David J. Kennedy, 1836. Erected in 1812 by German-born mechanic Lewis 

Wernwag, the Upper Ferry Bridge, also known as the Colossus, was an early masterpiece of American civil engineering. Spanning the 

Schuylkill River at Philadelphia, the 340-foot structure was the longest clear-span bridge in the world at the time of its construction, and 

the second-longest timber bridge built during the historic era of covered bridge construction. The Colossus carried traffic for a quarter 

of a century before it was destroyed by fire in 1838. Courtesy of Historical Society of Pennsylvania, Philadelphia, Pennsylvania, David J. 

Kennedy watercolors. 

Diffusion and Proliferation of Covered Bridges

Internal improvements were one of the first priorities of the young nation, with transportation 

networks desperately needed to improve communication, expand commerce, and unite the country. 

The Louisiana Purchase of 1803 doubled the land area of the United States, and, over the next 

half-century, American settlers headed west in increasing numbers. Timber bridges were an ideal 

solution to some of the many transportation hurdles facing settlers. Constructing a timber bridge 

only required readily available materials and common hand tools, and skilled carpenters could 

erect the superstructure of an average-sized bridge within a few weeks. Consequently, hundreds of 

covered bridges were constructed, first in major urban centers and then in increasingly rural areas 

as people moved westward. 
History of Covered Bridges in the United States 55

By 1810, adding roofs and siding to timber bridges was common practice in the United States, 

and there were covered bridges at most major crossings in southern and western New England, 

southeastern New York, eastern Pennsylvania, and New Jersey. From this core area, covered bridges 

spread to the northeast, south, and west at a rapid pace. By 1820, covered bridge building had 

reached northern New England, Maryland, southwestern Pennsylvania, and southeastern Ohio; 

by 1830, western Ohio and the Carolinas; by 1840, southern Indiana and the deep South; and, by 

1850, there were covered bridges in most regions with European settlements in the United States 

and Canada.20 The number of covered bridges continued to increase until about 1870, by which 

time there were well over ten thousand of them in the United States. Covered bridges would 

eventually be found in forty-one states. The few areas where covered bridges were not found include 

the heart of the Rocky Mountain region, and the 

northern and southern plains. The reasons for this 

vary from region to region but include the absence 

of major river crossings and readily available timber, 

topography more suited to other types of bridges, 

late-period settlement, and low population density.

Covered bridges helped achieve the safe, efficient, 

and economical overland transportation that was 

a key aspect of the nation’s growth and economic 

development. They were adapted to the needs of 

many types of transportation corridors, including 

turnpikes, canals, and railroads. The rapid growth of 

the railroads in the mid-1800s placed new demands 

on bridges. In particular, the increasing weight of 

locomotives and rolling stock and the need for 

rigidity encouraged technical advancements in the 

design of timber-truss bridges. 

Figure 3.7 This ca. 1880 photograph, taken in Contoocook 

Village, Hopkinton, New Hampshire, shows the 1849 Concord 

and Claremont Railroad Bridge on the left; another covered 

bridge, which still survives, replaced that bridge in 1889. The 

town of Hopkinton built the roadway bridge on the right in 

1853; it was replaced in 1936 with a stone-faced concrete 

bridge. Courtesy of Hopkinton Historical Society, Hopkinton, 

New Hampshire.

Developments in Timber-Truss Design

The social and economic climate of the nineteenth century favored the flowering of timberbridge building in America. The demand for bridges was great, wood was plentiful, and ambition 

was high. As a result, American builders produced, in rapid succession, a series of remarkable 

advancements in the design and construction of timber bridges. Between 1790 and 1840, timber 

bridge forms progressed from rudimentary pile-and-beam spans to scientifically designed, long-span 

trusses capable of carrying railroad loadings. These advancements addressed the overall challenge 

confronting bridge builders: to create economical and efficient structures that could span long 

distances, that were easy to erect and maintain, and that were strong enough to carry heavy, moving 

loads. Over time, this led to increased standardization in bridge design. 

The earliest significant covered bridges depended on arch construction, as builders sought to capitalize 

on the inherent strength of that structural form.21 Within a decade, however, truss construction came 

to dominate the field of American bridge building. Since the truss is the most efficient way to build 

long spans of wood, the majority of surviving covered bridges in the United States (more than 98 
56 Covered Bridges and the Birth of American Engineering

percent) are truss bridges.22 America’s early bridge builders relied on simple truss designs that had 

been used for roof framing since at least the Middle Ages, specifically the kingpost, queenpost, and 

multiple-kingpost trusses, which were sufficient for modest spans. These truss types continued to be 

used into the twentieth century. Approximately 24 percent of the extant covered bridges in the United 

States use one of these simple truss types.23 Later, these simple truss types became the basis for more 

sophisticated timber bridge designs, like the Burr, Town, and Howe trusses, that could span even 

greater distances. Dozens of patents were granted for timber bridges before 1850, but only a small 

percentage of these designs were ever successfully built. Fewer still gained widespread acceptance. 

More than 60 percent of the surviving covered bridges in the United States use trusses developed by 

a small group of American bridge builders in the first half of the nineteenth century. The major truss 

types and their creators are discussed below.

Figure 3.8 None of Theodore Burr’s Pennsylvania bridges remain, but many 

of the nation’s best examples of Burr-arch trusses are found in this state. Pine 

Grove Bridge (1884) completed over Octoraro Creek between Chester County 

and Lancaster County, is an example and one of at least twenty-five covered 

bridges erected by Capt. Elias McMellen, a prolific Pennsylvania bridge builder. 

HAER PA-586, sheet 2, Vuong Dang and Dave Groff, delineators, 2002.

Theodore Burr is a major figure 

in the history of covered bridge 

building. He is credited with 

the invention of the Burr-arch 

truss and with building a number 

of significant covered bridges 

throughout his twenty-year career. 

Born in Torrington, Connecticut, 

in 1771, Burr learned construction 

at an early age from his father, who 

was a miller and millwright. In 

1800, Burr built his first bridge, a 

simple timber-stringer span, across 

the Chenango River on the Catskill 

Turnpike at Oxford, New York. 

He subsequently experimented 

with a wide variety of timber arch 

designs for bridges that spanned 

the Hudson, Mohawk, Delaware, 

and Susquehanna rivers. In 1806 

and again in 1817, Burr received patents for the bridge design that bears his name.24 Burr’s 

masterpiece was the short-lived McCall’s Ferry Bridge (1815), which, with a clear span of 360 

feet, 4 inches, was the longest timber arch span erected during the historic era of covered bridge 

building. In 1822, Burr died under mysterious circumstances while supervising construction of 

a bridge at Middletown, Pennsylvania. The Union Bridge (1804), which spanned the Hudson 

River at Waterford, New York, was the last survivor of the bridges Burr designed; it was destroyed 

by fire in 1909.

Burr’s patented arch-truss configuration was not entirely new, as a similar plan had been published 

in Columbian Magazine in 1787, yet he was apparently the first bridge builder to make practical use 

of this design. The Burr-arch truss was an innovative design in which a separate segmental arch was 

superimposed on a multiple-kingpost truss. Its structural action was such that the arch bolstered 
History of Covered Bridges in the United States 57

the truss, while at the same time being stabilized by it, resulting in a complex interaction. A major 

advantage of this design, and a contributing factor to its popularity, was that it allowed for a level 

deck (in contrast to the arched decks of earlier spans built by Timothy Palmer and Lewis Wernwag), 

an important feature for multiple-span bridges, and, later, for railroad bridges. The Burr-arch truss 

was the first patented bridge truss to gain widespread acceptance among bridge builders, although 

Burr reportedly collected few royalties from it. It was also one of the most popular timber-truss 

types of the nineteenth century and beyond, as it was still used in some areas until about 1920.25 

Of the thousands of Burr-arch truss covered bridges that were built during the historic era of covered 

bridge building, about 185 examples survive in the United States, with some of the finest examples 

located in Pennsylvania and Indiana.26

By 1820, the potential span length of timber bridges had been extended to over 350 feet, and 

the practicality of the truss principle had been tested, even though its theory was still not fully 

understood. Combination arch-truss bridges were commonly built at major crossings, but the use of 

hewn timbers, traditional mortise and tenon joints, and the massive piers and abutments required 

to resist the thrust of the arch made construction of such bridges expensive and labor intensive. 

In response, builders began looking for ways to simplify construction so that substantial bridges 

could be built quickly and affordably in more locations. The fact that local governments (rather 

than private corporations) were beginning to finance public roads and bridges by this time further 

encouraged the development of simpler and more economical bridge designs.

Ithiel Town was an influential American architect and the 

inventor of the Town lattice truss, which was notable as one 

of the first attempts to eliminate traditional joinery in timberbridge design. Born in Thompson, Connecticut, in 1784, Town 

studied architecture as a young man under renowned architect 

Asher Benjamin. From 1829 to 1835, Town was a partner of 

Alexander Jackson Davis, who was a major proponent of the 

Greek Revival style of architecture. The firm of Town and 

Davis designed churches, state capitols, and other institutional 

and academic buildings along the East Coast. Town also made 

a significant contribution to the field of engineering when he 

began designing bridges. In 1818, he erected North Carolina’s 

first covered bridge across the Yadkin River near Salisbury.27 In 

1820 and again in 1835, Town patented his bridge truss and 

aggressively promoted the design, receiving patent royalties of 

one dollar per running foot of bridge.28 Ithiel Town supervised 

only a few bridges himself, none of which survive. 

Figure 3.9 Ithiel Town, Nathaniel Jocelyn,

oil on canvas, 36-1/8 x 29 inches. Courtesy

of National Academy Museum, New York,

Gift of George Dudley Seymour, 1941, 662-P.

The Town lattice truss design consisted of a lattice web of overlapping planks fastened together with 

treenails (wood pins). In 1821, Town published a pamphlet describing this design as “the most simple, 

permanent, and economical, both in erecting and repairing” and advocating this less expensive 

method of bridge construction as a solution to “the great and increasing demand for wooden bridges 
58 Covered Bridges and the Birth of American Engineering

Figure 3.10 Brown Bridge (1880) in Rutland County, Vermont, is an outstanding example of a Town lattice truss and the best 

surviving example of the work of Nichols Montgomery Powers, a prolific New England covered bridge builder. HAER VT-28,

sheet 2, Kimberly Clauer and Naomi Hernandez, delineators, 2002.

in all parts of this extensive country.”29 The advantage of the Town lattice truss extended beyond 

its ease of assembly. Since it was entirely free from arch action, it could theoretically be erected on 

less massive and, therefore, less costly abutments. The Town lattice system was used worldwide for 

bridges until well into the twentieth century.30 Of the thousands of Town-lattice covered bridges 

built during the historic era of covered bridge building, approximately 110 survive in the United 

States, primarily in the Northeast and South, with some of the finest examples located in Vermont.31

As early as the 1820s, there was a trend toward applying science to the technical problems associated 

with the nation’s industrial, geographic, and economic expansion. Institutions emerged to provide 

specialized academic training in science and technology. Established in 1802, the U.S. Military 

Academy at West Point, New York, was the first institution in the United States to offer academic 

instruction in civil engineering using a curriculum modeled after the École Polytechnique in France. 

The first engineering schools were established at Norwich, Vermont, in 1819 and Troy, New York, 

in 1824. Curriculums included applied math and science, as well as training in the design of roads, 

canals, and bridges. Mechanics’ institutes, such as the Franklin Institute, founded in Philadelphia 

in 1824, also promoted engineering knowledge, particularly among American working men. 

Publication of technical journals and textbooks also served to spread mathematical and scientific 

principles and fostered the growth of civil engineering as a profession.32

Stephen H. Long was one of the first bridge builders to apply mathematical theory to the practice 

of bridge design. Born in Hopkinton, New Hampshire, in 1784, Long was a prominent American 

engineer and military officer and the inventor of the Long truss. He graduated from Dartmouth 

College in 1809 and joined the U.S. Army Corps of Engineers in 1814. He led military surveying 

expeditions in the American West between 1817 and 1823 and subsequently spent several years 
History of Covered Bridges in the United States 59

helping to survey and build the Baltimore and 

Ohio Railroad. In 1829, Long built his first 

timber bridge over a railroad cut at Baltimore, 

Maryland. That structure served as the basis of 

a patent Long obtained in 1830 for a timber 

truss that introduced mathematical principles of 

engineering to American bridge building.33 Prior 

to this, bridge builders had relied upon empirical 

methods. By 1836, Long had twenty-six agents 

in eleven states, including his brother, Moses 

Long; his nephew, Horace Childs; and Stephen 

Daniels, father of Indiana bridge builder J. J. 

Daniels. In addition to his army duties, Long 

served as a consultant to various railroads until 

1856, when he was put in charge of navigation 

improvements on the Mississippi River. In 1861, 

Long was called to Washington, D.C., to serve as 

commander of the Corps of Engineers, a position 

he held until his retirement in 1863. 

Figure 3.11 “Major. Stephen Harriman Long on the Rocky 

Mountain Expedition, 1819-1820, attribut ed to Titian Ramsay 

Peale. Courtesy of Catherine Dail Fine Art, New York. 

The Long truss is a traditionally framed panel truss with paired diagonal braces and single 

counterbraces crossing within each panel. This design is of engineering interest because it introduced 

the modern concept of prestressing—the creation of permanent stresses in a structure to improve 

its performance under loading—achieved by driving wedges into counterbrace connections to 

increase rigidity. The use of counterbraces, Long explained, would result in “stiffness of structure, 

and exemption from trembling, springing and oscillations of every kind.”34 Some of the first truss 

railroad bridges in the United States used the Long truss because of its ability to carry heavy loads 

without excessive deflection. Although the Long truss advanced understanding of structural behavior 

and scientific analysis, it eventually fell out of favor because, although it eliminated some tension 

connections, it still required intricate framing details. None of the bridges designed by Stephen 

Figure 3.12 Eldean Bridge (1860) 

in Miami County, Ohio, is one of the 

best surviving examples of a Longtruss covered bridge. Built by local 

contractors James and William Hamilton, 

the bridge features wooden wedges 

driven between the counterbraces 

and lower chords to prestress the 

structure. HAER OH-122, sheet 2, 

William Dickinson, delineator, 2002.
60 Covered Bridges and the Birth of American Engineering

Long survive, but eight Long trusses built during the historic era of covered bridge building are 

scattered throughout the eastern United States, with the purest examples having wedges acting on the 

counterbraces. While it is not known how many covered bridges have this feature, the Eldean Bridge 

(1860) in Miami County, Ohio, and Blair Bridge (1869) in Grafton County, New Hampshire, do.35

Millwright Peter Paddleford, born in 1785 in Littleton, New Hampshire, was a proponent of the 

Long truss and built several bridges of this type before developing his own truss design in the early 

1830s. Paddleford built a number of significant covered bridges, including two across the Connecticut 

River between Vermont and New Hampshire, as well as numerous lesser-known spans in the upper 

reaches of those two states and in western Maine. 

The Paddleford truss was a multiple-kingpost truss with long counterbraces extended over more than 

one panel, which helped distribute loads and increase the truss’s rigidity. Although never patented, 

the Paddleford truss dominated covered bridge construction throughout northern New England for 

over half a century. This was due, in part, to the work of Peter’s son, Philip H. Paddleford, who went 

into partnership with his father in 1835 and continued building bridges throughout his career. Of the 

dozens of Paddleford-truss covered bridges built during the historic era of covered bridge building, 

twenty-one examples survive in New England, although none are the work of the designer himself.36

In the 1830s, demand increased for standardized bridges that could be rapidly erected to keep pace 

with the growth of the nation’s railroad network. This demand was a major impetus to the development 

of American bridge-building technology. Training in mechanics and strength of materials allowed 

bridge designers to understand how the various members of a bridge functioned under loading and 

then design them accordingly. As scientific understanding of truss action increased, the focus turned 

to building bridges that were not only economical but also structurally efficient. 

Figure 3.13 William Howe, Otis H. Cooley, 

daguerreotype, 5.5 x 4.3 cm, ca. 1850. Courtesy

of National Portrait Gallery, Smithsonian Institution, 

NPG.2008.58.

Born in 1803 in Spencer, Massachusetts, William Howe 

was a millwright and the inventor of the Howe truss, 

which was the first bridge truss type to use iron for 

primary structural members. In 1839, Howe built his 

first bridge for the Western Railroad across the Quaboag 

River in his hometown. The structure so impressed 

railroad engineer George Washington Whistler that he 

gave Howe the contract for the seven-span, 1,330-footlong Western Railroad Bridge (1841) at Springfield, 

Massachusetts.37 In 1840, Howe received a patent 

for a truss design that used adjustable wrought-iron 

rods (instead of wood posts) for the tension members. 

This arrangement overcame the inherent difficulty of 

creating tension connections in wood structures and 

allowed for easier and more efficient prestressing of the 

members.38 That same year, Howe moved to Springfield, 

Massachusetts, where he entered the bridge-building 

business with his brother-in-law, Amasa Stone Jr. of 
History of Covered Bridges in the United States 61

Cleveland. In 1842, Stone bought the rights to Howe’s patent and formed a bridge company with 

railroad magnate Azariah Boody. Boody, Stone, and Company continued under various names 

until the late nineteenth century.39 Howe continued to sell patent rights to companies throughout 

the country and received royalties that earned him a sizeable fortune. 

Railroads favored the Howe-truss design because it had standardized framing connections incorporating 

prefabricated iron elements and could be quickly erected and easily adjusted. The American Society 

of Civil Engineers praised the Howe truss as “the most perfect wooden bridge ever built,” adding 

“others have been designed of greater theoretical economy; but for simplicity of construction, rapidity 

of erection, and general utility it stands without rival.”40 Used extensively for railroad bridges in 

North America and abroad during the mid-nineteenth century, the combination wood/iron Howe 

truss was gradually superseded by all-metal Howe truss structures, but it remained one of the most 

important timber-truss types of the nineteenth century. Of the hundreds, perhaps thousands, of 

Howe-truss covered bridges built during the historic era of covered bridge building, about 100 

examples survive—although none by Howe himself—primarily in the Midwest and Pacific Northwest. 

The purest examples of the widespread commercial Howe truss have cast-iron angle blocks and the 

standard endpost treatment of two vertical wood posts with an iron tension rod between them and 

wood angle blocks on the final braces.41

Figure 3.14 Built by Joseph A. Britton, 

one of Indiana’s most prolific covered 

bridge builders, Pine Bluff Bridge (1886)

in Putnam County, Indiana, is an exceptionally fine example of a timber Howe 

truss, featuring the cast-iron bearing 

blocks and standard endpost treatment 

that were common in late-nineteenthcentury timber bridges of this type.

HAER IN-103, sheet 2, Charu Chaudhry,

delineator, 2002.

Railroad engineer Thomas Willis Pratt was born in Boston, Massachusetts, in 1812, where his 

father, Caleb Pratt, was a noted architect. After attending the Rensselaer School (now Rensselaer 

Polytechnic Institute), Thomas Pratt served as engineering assistant for the U.S. Army Corps of 

Engineers, building drydocks at Charleston, South Carolina, and Norfolk, Virginia. He subsequently 

was employed in the field of railroad construction, where he began designing bridges. In 1844, 

Thomas and Caleb Pratt obtained a patent for a combination panel truss that featured vertical 

wood posts at each panel point and diagonal iron rods crossing within each panel.42 While not 

immediately popular for wood bridges, the design was later widely adopted in a modified all-metal 
62 Covered Bridges and the Birth of American Engineering

version. Over the course of a career that spanned forty years, Thomas Pratt became a prominent 

civil engineer who supervised the construction of several major railroad lines in the Northeast and 

built a number of important railroad bridges. Today, he is remembered for the invention of the 

Pratt truss, a highly significant American bridge design, although he received few patent royalties 

from it.43

The Pratt truss reversed the configuration 

of the 1840 Howe truss, placing the shorter 

web members (verticals) in compression and 

longer web members (diagonals) in tension, 

which reduced the danger of structural failure 

through buckling. Developed at a time when 

railroads were placing new demands on 

bridges and the structural action of trusses 

was just beginning to be understood, the 

Pratt truss was one of several truss types that 

heralded the transformation from empirical 

to scientific bridge design. Few timber Pratt 

trusses were built and only one surviving 

example, the Sulphite Railroad Bridge in 

Merrimack County, New Hampshire (1896), 

somewhat resembles the patent. After the Civil 

War, the Pratt-truss design was successfully 

adapted, with some modifications, to metal bridge building. The modified Pratt truss came to be 

favored for its strength and simplicity, and from the late nineteenth century well into the twentieth 

century, it was the standard American truss for moderate-size, metal railroad and highway spans. A 

few combination wood/metal Pratt-truss bridges were built and covered, which was presumably a 

back-formation from the all-metal version. There are two surviving combination wood/metal Pratttruss covered bridges in California: Honey Run Bridge in Butte County (1886) and Felton Bridge 

in Santa Cruz County (1892).44

Figure 3.15 Built by the American Bridge Company in 1886, 

Honey Run Bridge in Butte County, California, is one of only 

three surviving Pratt-truss covered bridges in the United States. 

Invented in 1844, the Pratt truss reversed the configuration of 

the 1840 Howe truss to reduce the chance of structural failure 

through buckling. Few timber Pratt truss bridges were built, 

but the design was later adapted to metal-truss bridges, and it 

remained the standard American truss type for moderate road 

and railroad spans well into the twentieth century. HAER CA-312, 

sheet 6, Jeremy Mauro and Ben Shakelton, delineators, 2012.

Covered Bridge Architecture 

The earliest covered bridges were magnificent structures, both in terms of engineering and 

architecture. Financed with private capital, the early turnpike bridges were all custom-built 

structures, wide enough for two lanes of travel, with highly ornamented exteriors. The Schuylkill 

Permanent Bridge was probably one of the most extravagant, but other grand covered bridges once 

existed at major river crossings along the East Coast.

By 1820, covered bridges were much more common and less ornate. Covered bridges built by towns 

and counties were often quite plain in appearance. Architectural variations occurred, often on a 

regional level, reflecting the use of local materials and building traditions. For example, covered 

bridges in southeastern Pennsylvania often had long stone-masonry approaches and stepped gables, 

while many of the covered bridges in Madison County, Iowa, featured flat roofs and arched portals. 

Covered bridges erected by the Kennedy family of Rush County, Indiana, bore ornamental scrollwork 
History of Covered Bridges in the United States 63

and cornice brackets, and those built during the 1930s in Blount County, Alabama, were covered 

with corrugated metal roofing and siding. In Oregon, where covered bridges were built according 

to state-issued plans into the 1950s, each county developed its own distinctive bridge-housing style.

Because the housing was considered expendable and was expected to be periodically replaced, the 

majority of covered bridges were left unpainted until the mid-twentieth century. Those that were 

painted might be red or white, but other colors were also used. By the 1950s, Americans decided, for 

reasons yet unknown, that covered bridges should be red, and within two decades, approximately 

one-third of the covered bridges in the United States were painted that color. The term “covered 

bridge red” even slipped into modern advertising to market such items as paint, yarn, and wine. 

A popular Christmas card image of the Bedell Bridge, which spanned the Connecticut River at 

Newbury, New Hampshire, from 1866 to 1979, was even tinted red, although the bridge itself had 

never been painted.45

Figure 3.16 Top Left: 3.16a) Dreibelbis Station Bridge (1869) in 

Berks County, Pennsylvania, exhibits the masonry approach walls

and stepped gables that were original characteristics of covered 

bridges in southeastern Pennsylvania. HAER PA-587-4, Jet Lowe, 

photographer, 2002. Top Right: 3.16b) Holliwell Bridge (1880)

in Madison County, Iowa, exhibits the nearly flat roof and gracefully arched portals that were used in several of the county’s 

covered bridges. HAER IA-64-27, Jet Lowe, photographer, 2004.

Left: 3.16c) Swann Bridge (1933) in Blount County, Alabama,

is clad in the corrugated metal roofing and siding adopted to 

house a number of the county’s covered bridges in the 1930s.

HAER AL-201-4, Jet Lowe, photographer, 2002.

In addition to regional architectural styles, the height of the trusses and location of the bridge deck 

could also dictate the bridge housing. Pony-truss (or low-truss) bridges, which were often used for shorter 

spans, required no overhead bracing, so each of the trusses might be individually housed (these are 

referred to as “boxed” trusses). Sometimes, through-truss (or high-truss) bridges were also “boxed,” or 

housed, in a similar manner, by enclosing the trusses without adding a roof. Deck-truss bridges, in which 

the deck is carried on the upper chords, were typically used in locations with steeply sloping terrain, 

where placing the trusses below the travelled way allowed for shorter and less expensive substructure 

components. Timber deck-truss bridges often had a roof and siding located below the deck.46
64 Covered Bridges and the Birth of American Engineering

Covering a wood bridge is the most reliable way to protect it from decay, but in some instances 

builders did away with the housing in favor of treating the timbers with chemical preservatives or 

protecting the upper chords with sheet metal. Non-housed timber-truss bridges share a common 

history with covered bridges, but very few have been preserved.47

Figure 3.17 Left: 3.17a) The Boston and Maine Railroad used boxed pony-truss bridges for short spans well into the twentieth

century. Moose Brook Bridge (1918) in Coos County, New Hampshire, was one of six surviving boxed pony-truss bridges in the

United States until it was seriously damaged in an arson fire in 2004. HAER NH-48, sheet 6, Bradley M. Rowley and Anne E. Kidd,

delineators, 2009. Right: 3.17b) The Great Northern Railway used boxed through-truss bridges for moderate spans well into

the twentieth century. Harpole Bridge (1922) in Whitman County, Washington, is the last surviving boxed through-truss bridge

in the United States. HAER WA-135-5, Jet Lowe, photographer, 1993.

Wood versus Iron

Throughout the nineteenth century, interest grew in a new structural material: iron. The tensile 

strength of iron, coupled with its resistance to fire, rot, and insects, made it an appealing material, 

particularly on railroads where rigid bridges that were easy to erect and maintain and capable of 

carrying increasingly heavy loads were desired. Between 1836 and 1839, Capt. Richard Delafield of 

the U.S. Army Corps of Engineers designed and oversaw construction of America’s first iron bridge 

across Dunlap’s Creek on the National Road at Brownsville, Pennsylvania. That innovative structure 

was an 80-foot, cast-iron arch consisting of five tubular arch rings supporting the roadway.48 Other 

engineers tinkered with ideas for iron-truss bridges in the 1840s, but enthusiasm for the use of 

this new material in structures was tempered by periodic structural failures, which led to lingering 

suspicion of iron in the public mind. Some designers merely substituted iron parts directly for wood, 

but ignoring the differences in the structural properties of the two materials figured prominently 

in the 1876 collapse of an iron bridge in Ashtabula, Ohio, that killed eighty-three people.49

Due to these periodic failures, the adoption of iron occurred relatively slowly. As is often the case when 

a new building material is introduced, there were successes and failures—radical advancements and 

technological dead ends. As engineers worked to better understand the behavior of iron structures, 

bridge builders continued to alternate between wood and iron for much of the nineteenth century. For 

all of its benefits, iron also had its drawbacks: it was expensive, difficult to manufacture, susceptible to 

corrosion, and it often failed without warning. Ultimately, the advantages that iron construction afforded, 
History of Covered Bridges in the United States 65

combined with the disadvantages of timber construction (susceptibility to fire and rot and the need 

for periodic maintenance), led many engineers and public officials to view timber bridges as obsolete. 

In the post–Civil War era, covered wood bridges were still economical, except for very long spans, 

and there were still opportunities for innovative timber-bridge builders to remain competitive, 

especially in regions where timber was readily available.50 The surest route to reducing the cost of 

any construction is to minimize the quantity of materials that goes into it, and many timber bridges 

were overbuilt for the loads they carried. By employing the methods of mathematical stress analysis 

described by engineer Squire Whipple in his 1847 Essay on Bridge Building, builders could proportion 

structural members in the most efficient manner possible, and, in doing so, cut costs.51 From the 

1860s onward, several inventors addressed this challenge and used the advances in civil engineering 

to build timber bridges less expensively so they could compete with iron-bridge manufacturers.

Robert W. Smith, born in Tippecanoe City, Ohio, in 1833, 

was the inventor of the highly successful Smith truss. Smith 

was educated at home until he was 15 and only attended public 

school for six weeks to study geometry. He learned carpentry 

from his father and older brother, who were barn builders. Early 

in his career, Smith ran a woodworking shop and lumberyard 

but eventually turned his attention to bridges. In 1867, Smith 

patented a bridge truss that, for a short time, allowed wood 

bridges to successfully compete with iron ones.52 By 1869, Smith 

had established the Smith Bridge Company factory in Toledo, 

Ohio. Bridges were prefabricated to order, shipped to their 

sites, and erected under the supervision of company agents. The 

company built hundreds of covered bridges during the 1870s 

and successfully made the transition to the manufacture of iron 

bridges. In 1890, the Smith Bridge Company ceased operations, 

and the plant was sold to the Toledo Bridge Company. Of the hundreds of Smith-truss covered 

bridges built during the historic era of covered bridge building, twenty-three examples survive in 

the United States, primarily in Ohio and Indiana.53

Figure 3.18 Portrait of Robert W. Smith.

North & Oswald, Toledo, Ohio, photographers, 

ca. 1880. Courtesy of Miriam Wood Collection.

The Smith truss featured parallel chords connected by a series of intersecting inclined posts and 

braces and was notable for being both economical and strong. Smith subsequently made several minor 

modifications to his design, and he received a second patent in 1869, but all Smith trusses followed 

the same general layout, with one, two, or three web planes, depending upon the length of the span.54

Other inventors followed Smith’s lead, and at least two received patents that were geometrically similar 

to the Smith truss. In 1870, Isaac H. Wheeler of Sciotoville, Ohio, patented a modified Smith truss 

with offset compression members and an intermediate chord along the midline of the truss.55 Two 

years later, Reuben L. Partridge of Marysville, Ohio, patented another modified Smith truss with metal 

bearing shoes that were intended to reduce the amount of material required for the chords.56 Neither 

the Wheeler nor the Partridge trusses ever entered the mainstream of covered bridge building, but 

they illustrate a mid-nineteenth-century flowering of innovation in American timber-bridge design.
66 Covered Bridges and the Birth of American Engineering

Figure 3.19 Built for the California Powder Works in 1872, Powder Works Bridge in Santa Cruz, California, is the only surviving 

example of the Smith Bridge Company’s operations on the West Coast, and it represents the last effort to market timber bridges 

on a national scale. The 180-foot span required a heavily-built structure using three planes of web members (Smith truss, Type 

4), because the bridge carried pedestrians and wagons as well as horse-drawn freight cars on a narrow-gauge railroad track 

until the black powder manufacturing plant closed in 1914. Today the bridge carries limited vehicular traffic within a private 

residential community. HAER CA-313, sheet 9, Jeremy Mauro, Ben Shakelton, and Christopher H. Marston, delineators, 2012.

Decline of Covered Bridge Building

By the 1880s, bridge builders had learned how to best utilize the strengths of iron, and the material 

came to dominate bridge construction. Iron and steel bridges began rapidly replacing timber bridges 

across the country in the last two decades of the nineteenth century. Many towns and counties 

debated the costs of construction and maintenance of different types of bridges and were influenced 

by what neighboring towns and counties were building, which were often the prefabricated metal 

bridges widely marketed by bridge manufacturing firms. Railroads enabled manufacturers to ship 

prefabricated metal bridges to distant markets and thereby compete with local builders for contracts. 

The cost-effectiveness of iron, and later steel, was largely responsible for the decline of timber-bridge 

building in the early twentieth century.

In addition, the last decades of the nineteenth century saw the 

rise of the Good Roads Movement, as farmers and bicyclists and, 

later, increasing numbers of automobile users began to agitate for 

paved roads and modern bridges. Most engineers viewed wood as 

a material outmoded for modern purposes. Lacking incentives to 

maintain aging timber spans, state highway departments across 

the country began bypassing or demolishing covered bridges and 

replacing them with steel and concrete structures that were wider, 

more open, and better suited for heavy, motorized vehicles traveling 

at increasingly faster speeds. Thus, during the first decades of the 

twentieth century, most Americans considered covered bridges 

neither particularly useful nor worthy of devotion; instead, they 

often viewed them as archaic, unsightly, and dangerous.

Figure 3.20 Modern spans replaced

many covered bridges in the early 

twentieth century. After fifty years of 

service, the San Marcos River Bridge (1845) 

in Gonzales County, Texas, was replaced 

with a metal-truss span in 1904. Courtesy 

of Texas Department of Transportation.
History of Covered Bridges in the United States 67

Birth of a Cultural Icon

The automobile brought physical changes to the landscape and was also the means by which growing 

numbers of individuals experienced their rapidly changing world. In the face of the technological 

and industrial advances of the early twentieth century, covered bridges within pastoral landscapes 

generated powerful feelings of nostalgia, and public interest in these picturesque landscape features 

began to grow.

In the 1930s and 1940s, covered bridges 

reemerged in the public imagination, 

becoming the subject of folklore and 

legend. They also regularly appeared in 

American popular culture as nostalgic, 

romantic, or mysterious elements. 

Many examples can be found in midtwentieth-century literature, cartoons, 

music, radio, film, and television. 

Advertisers, hoping to associate their 

products with positive images of an 

idealized America, used covered bridges 

to market everything from insurance 

and thermal underwear to cigarettes 

and beer. A number of well-known companies, including Coca-Cola, Ford, McDonald’s, and Sears, 

used covered bridges in mid-twentieth-century advertising campaigns. 

Figure 3.21 In the late nineteenth and early twentieth centuries, advertisements were sometimes painted on the exteriors of covered bridges in 

prominent locations. As a consequence, the Portland-Columbia Bridge 

(1869) spanning the Delaware River between Pennsylvania and New Jersey 

was known as the “Coca-Cola Bridge” in the early twentieth century. 

Hurricane-related floods in 1955 destroyed the bridge. Edward Hungerford, 

photographer, 1916. Courtesy of Thomas E. Walczak Collection. 

Figure 3.22 Roseman Bridge (1883) is one of nineteen covered bridges built in Madison County, Iowa, in the nineteenth century 

and one of only five that survive. Prominently featured in the 1995 movie adaptation of Robert James Waller’s romantic novel, The 

Bridges of Madison County, the bridge has since become a popular wedding venue. HAER IA-95-5, Jet Lowe, photographer, 2004.
68 Covered Bridges and the Birth of American Engineering

Beginning in the 1950s, people built small-scale covered bridges for their backyards and businesses, 

sometimes even demanding that “replicas” of old covered bridges be built on public roads. Curiously, 

while the housing of covered bridges was traditionally a practical consideration to extend the life 

of a timber bridge, it often became the primary focus of folk-art bridges and replicas. In many 

instances, the covering was merely a shed built over a concrete slab or steel-stringer bridge, creating 

the illusion of a covered bridge.57 

By the 1960s and 1970s, the iconic status of the covered bridge in the American collective memory 

resulted in communities across the country recognizing the historical importance of covered bridges 

and beginning to take steps to preserve them for future generations. In the last few decades, many 

covered bridges have become cherished local landmarks and symbols of community pride. Although 

covered bridges continue to be lost to floods, fires, neglect, and vandalism, far fewer are destroyed in 

the name of progress than previously, and many have been the objects of intensive preservation efforts, 

as described in chapter 7. 58 

Historic Era of Covered Bridge Building Ends 

While construction of covered bridges had virtually ceased in the rest of the country, there was a 

resurgence in Oregon in the first half of the twentieth century, when wartime steel shortages and 

the economic downturn of the Great Depression encouraged covered bridge construction in this 

region of abundant virgin timber. In 1915, the Oregon State Legislature passed legislation requiring 

that county bridges costing more than $500 be built under the supervision of the newly-formed 

Oregon State Highway Commission. After investigating various bridge types, state highway engineers 

calculated that a well-built, covered, wood bridge could last as long as a steel bridge and cost much 

less to build. They subsequently developed standard plans for covered bridges that were designed 

specifically for motorized vehicles. Over the next four decades, county engineers and road crews 

used these state-issued plans to build approximately two hundred covered bridges on secondary 

roads in western Oregon.59 

The covered bridges designed by the Oregon State Highway Commission were wider, sturdier, 

and more open than their nineteenth-century counterparts, since they were built to accommodate 

motorized, rather than horse-drawn, vehicles. Most of these bridges used a simplified Howe truss 

without counterbraces. State engineers recommended the Howe truss because it required minimal 

steel and could be built rugged enough to meet modern load requirements. The availability of 

large-dimension virgin timber in western Oregon allowed builders to return to traditional timberframing practices (for example, mortising the braces directly into the chords, rather than using angle 

blocks), and some bridges used hand-hewn, single-stick chords, rather than built-up plank chords.60

The resurgence of covered bridge building in western Oregon remained strong through the 1920s 

and 1930s, and lasted through the 1940s in some counties. In 1944, approximately 230 covered 

bridges were in use on rural roads in the state.61 After World War II, the price of lumber and labor 

dramatically increased, making it comparatively less expensive to build new spans of steel or concrete. 

By the late 1940s, few covered bridges were being built anywhere in the United States, even in the 

timber-rich region of the Pacific Northwest. The historic era of American covered bridge building 

ended in Oregon in the 1950s.62
History of Covered Bridges in the United States 69

Figure 3.23 Built by the Linn County Engineering Department in 1941, Larwood Bridge is one of the best surviving examples 

of Oregon’s standard-plan Howe trusses. HAER OR-124-13, Jet Lowe, photographer, 2004.

Revival Era of Covered Bridge Building Begins

By the time the historic era of covered bridge building ended in the Pacific Northwest, a new era 

of covered bridge building was beginning in the Northeast. As early as the 1930s, covered bridges 

were becoming tourist attractions. Growing public interest in preserving covered bridges eventually 

led to the building of modern copies for nostalgic reasons. This revival of covered bridge building 

occurred at different times in different regions of the country and followed a period generally 

spanning several decades when covered bridges were widely regarded as obsolete in each region. 

The revival-era covered bridges are distinct from their historic-era counterparts in that they were 

built, at least in part, for sentimental reasons, rather than purely economic ones.

The replacement Hancock-Greenfield Bridge (1937) in Hillsborough County, New Hampshire, is the 

first known example of a covered bridge built primarily for nostalgic reasons in the United States.63 

That bridge remained an anomaly until the 1950s, when the Massachusetts Department of Public 

works began replacing old covered bridges with new ones, at the urging of local communities. These 

early revival-era covered bridges were very different in construction and appearance from the bridges 

they replaced, as they were built to modern highway specifications and used timber connectors 

rather than traditional timber-framing techniques. As time went on, some twentieth-century timber 

framers began to build modern covered bridges in much the same manner as traditional ones. Built 

to replace an aging iron span, the Union Street Bridge (1968–69) in Woodstock, Vermont, was 

one of the first revival-era covered bridges to utilize traditional trusses and framing techniques. 

These bridges, and several others built around the same time, ushered in a revival of covered bridge 

building that continues today in a few scattered parts of the country.64
70 Covered Bridges and the Birth of American Engineering

Figure 3.24 The historic covered bridge era ended in the Pacific Northwest. Yet, as this map demonstrates, the vast majority 

of extant historic covered bridges can be found east of the Mississippi River. Map created by James Stein and Matthew Stutts, 

Cultural Resources Geographical Information System facility, National Park Service, 2004, 2014.

Conclusion

Covered bridges were a practical and economical engineering solution to crossing rivers in the 

nineteenth century; as such, they played a critical role in the growth of this nation by facilitating 

transportation, settlement, and commerce. They also represent a period of great technological 

achievement that occurred in the early to mid-nineteenth century, during which engineers and 

builders perfected designs for sturdy and cost-effective bridges that could span long distances and 

safely carry heavy, moving loads. The basic engineering principles applied during America’s historic 

era of timber-bridge building continue to be used by engineers around the world today. Of the 

more than ten-thousand covered bridges that once existed throughout the country, nearly sevenhundred covered bridges built during the historic era of covered bridge construction still survive in 

twenty-nine states.65 Many of those are still in use on public roads, reaffirming that these venerable 

structures are more than just quaint relics of a bygone era; they are an integral part of our political, 

social, cultural, and engineering heritage that merits preservation.
History of Covered Bridges in the United States 71

Endnotes

 1 Before the nineteenth-century explosion of American covered bridge building, nearly all covered 

bridges were constructed in the forested regions of central Europe. American scholars have recently 

become aware of hundreds of ancient covered bridges in China; however, most of these bridges were 

built for pedestrian use, and their construction techniques and reasons for covering differ from the 

Western tradition. An excellent reference is Ronald G. Knapp, Chinese Bridges: Living Architecture from 

China’s Past (Singapore: Tuttle Publishing, 2008).

2 This is only a rough estimate of known covered bridges that existed ca. 1870. Initial data compiled by 

the Covered Spans of Yesteryear project, http://www.lostbridges.org, suggests that this figure may be 

too low.

3 While bridges built during the more recent revival era of covered bridge construction will increasingly 

be regarded as “historic” as they age over time, they will remain a product of a period of covered bridge 

construction that was markedly different from that of their forebears.

4 In 55 BC, Julius Caesar ordered the world’s first major timber bridge built across the Rhine River near presentday Koblenz, Germany. Considered a masterpiece of military engineering, Caesar’s Bridge was a pile-and-beam 

structure estimated at between 460 and 1,300 feet long. 

5 For more on the Grubenmann brothers and their bridges, see Angelo Maggi and Nicola Navone, John 

Soane and the Wooden Bridges of Switzerland: Architecture and the Culture of Technology from Palladio 

to the Grubenmanns (London: John Soane Museum, 2003). For a list of surviving covered bridges 

in Switzerland, see David W. Wright, ed., World Guide to Covered Bridges (National Society for the 

Preservation of Covered Bridges, 2009), 236–71.

6 Isaac Weld Jr. describes some of the challenges of overland travel in Travels Through the States of 

North America and the Provinces of Upper and Lower Canada During the Years 1795, 1796 and 1797

(London: John Stockdale, 1807).

7 The Great Bridge (1662) across the Charles River at Boston, Massachusetts, and Sewell’s Bridge (1761) 

across the York River at York, Maine, were notable exceptions. Both bridges consisted of a series of 

simple beam spans. The Great Bridge was supported by stone-filled log cribs, while the York River 

Bridge used timber pile trestles.

8 The Massachusetts Spy, or, American Oracle of Liberty (Worcester, Mass.), February 10, 1785, 3.

9 Andrea Palladio, The Four Books of Architecture (London: Giacomo Leoni, 1716–20), book 3, plates 

III–V.

10 John Bliss’s 124-foot Leffingwell Bridge (1764–77) across the Shetucket River at Norwich, 

Connecticut, was described as being “supported by Geometry work above” and may have been the first 

use of the truss principle in American bridge design; however, Timothy Palmer was the first builder to 

use the truss in a long-span bridge. Frances Manwaring Caulkins, The History of Norwich, Connecticut

(Norwich, Conn.: Thomas Robinson, 1845), 348, and Richard Sanders Allen, Covered Bridges of the 

Northeast (Brattleboro, Vt.: Stephen Greene Press, 1957), 12.

11 The Essex Merrimack River Bridge was considered a great engineering achievement but was denounced 

as a hindrance to navigation. Thus, in 1810, a novel iron chain suspension bridge designed by Judge 

James Finley of Pennsylvania replaced the main span. See “Essex-Merrimack Bridge,” HAER No. MA93.

12 “Description of the Essex Merrimack River Bridge,” Massachusetts Magazine, May 1793, 1.

13 Helen Park, “A List of Architectural Books Available in America Before the Revolution,” Journal of the 

Society of Architectural Historians 20, no. 3 (October 1961): 128.
72 Covered Bridges and the Birth of American Engineering

14 Timothy Palmer built at least ten major bridges between 1792 and 1805: Essex Merrimack River 

Bridge (1792), Newburyport, Mass.; Andover Bridge (1793), Lawrence, Mass.; Piscataqua Bridge 

(1794), Newington, N.H.; Haverhill Bridge (1794), Haverhill, Mass.; Rocks Bridge (1795), West 

Newbury, Mass.; Little Falls Bridge (1796), Georgetown, Md.; Cornish Bridge (1796), Cornish, N.H.; 

Kennebec River Bridge (1799), Augusta, Maine; Schuylkill Permanent Bridge (1804), Philadelphia, Pa.; 

and Easton Bridge (1805), Easton, Pa. None of Palmer’s bridges survive.

15 Built in 1697, the triple stone-arch Pennypack Creek Bridge is the oldest extant roadway bridge in the 

United States. See “Pennypack Creek Bridge,” HABS No. PA-1786 and HAER No. PA-465. Quote 

from Richard Peters, A Statistical Account of the Schuylkill Permanent Bridge Company (Philadelphia: 

Jane Aitken, 1807), 6. 

16 Fortescue Cuming, Sketches of a Tour to the Western Country, 1807–1809 (Pittsburgh: Cramer, Spear, and 

Eichbaum, 1810), 25.

17 Peters, Statistical Account, 49.

18 Peters, Statistical Account, 34.

19 The writings of both Richard Peters and Owen Biddle suggest that the Schuylkill Permanent Bridge 

was the only covered bridge in the United States at the time of its completion. See Peters, Statistical 

Account, quote from 34, 46–51, and Owen Biddle, The Young Carpenter’s Assistant (Philadelphia: 

Benjamin Johnson, 1805), 96. See also Richard Sanders Allen, “Comment and Commentary on the 

‘The First Covered Bridge in America,’” Covered Bridge Topics 11, no. 2 (Summer 1953): 4.

20 Fred Kniffen, “The American Covered Bridge,” Geographical Review 41, no. 1 (January 1951): 119.

21 Because little was known about the structural action of trusses, early long-span timber bridges 

often combined trusses with arches. The ancient structural form of the arch utilizes the principle of 

compression to span long distances and is the only way to construct long spans of masonry. Most major 

bridges in Europe were masonry arches and British books available in eighteenth-century America 

discussed bridge building solely in terms of arch construction. In America, with few exceptions 

(dependent on the availability of high-quality stone), masonry bridges were too expensive and laborintensive to build, so the arch form was adapted to less expensive timber construction.

22 Only six extant covered bridges in the United States use arch construction instead of truss 

construction. Three tied-arch covered bridges survive in Vermont, and three polygonal-arch covered 

bridges survive in Virginia; all but one of these bridges span modest distances of less than 50 feet. See, 

for example, “Swallow’s Bridge,” HAER No. VT-36 and “Sinking Creek Bridge,” HAER No. VA-126.

23 Noteworthy examples of the kingpost truss include “Neal Lane Bridge,” HAER No. OR-126 and 

“Pine Brook Bridge,” HAER No. VT-37; examples of the queenpost truss include “Morgan Bridge,” 

HAER No. VT-33 and “Flint Bridge,” HAER No. VT-29; and examples of the multiple-kingpost truss 

include “Humpback Bridge,” HAER No. VA-1 and “Taftsville Bridge,” HAER No. VT-30. Additional 

examples of these truss types are listed in the appendix.

24 Burr’s 1806 patent was lost in the 1836 U.S. Patent Office fire, but the 1817 patent was recovered. See 

Theodore Burr, U.S. Patent No. 2,769X, April 3, 1817. See also, Hubertis M. Cummings, “Theodore 

Burr and His Bridges Across the Susquehanna,” Pennsylvania History 23, no. 4 (October 1956): 484.

25 The Edna Collins Bridge (1922) in Putnam County, Indiana, was the last Burr-arch truss covered 

bridge built in the United States during the historic era of covered bridge building.

26 Noteworthy examples of the Burr-arch truss include “West Union Bridge,” HAER No. IN-105 and “Hyde 

Hall Bridge,” HAER No. NY-330. Additional examples of this truss type are listed in the appendix. See 

also Joseph D. Conwill, “Burr Truss Bridge Framing,” Timber Framing 78 (December 2005), 4.

Endnotes
History of Covered Bridges in the United States 73

27 The Yadkin River Bridge was replaced sometime after the Civil War

28 Ithiel Town, U.S. Patent No. 3,169X, January 28, 1820.

29 Ithiel Town, A Description of Ithiel Town’s Improvement in the Construction of Wood and Iron Bridges: 

Intended as a General System of Bridge-Building (New Haven, Conn.: S. Converse, 1821), 3–4.

30 The Town lattice truss was also adapted for roof trusses, reportedly used in the Second Presbyterian Church 

(1835), Madison, Ind.; the First Presbyterian Church (1832), Fayetteville, N.C.; the Mormon Tabernacle (1864), 

Salt Lake City, Ut. (see HAER No. UT-1); and the Gov. Thomas Bibb House (1836), Huntsville, Ala. See Joseph 

D. Conwill, “Town Lattice Trusses by the Master Himself,” Covered Bridge Topics 54, no. 1 (Winter 1996): 

3–4; “Town Lattice Roof Trusses in Madison, Indiana,” Covered Bridge Topics 62, no. 2 (Spring 2004): 6.

31 Noteworthy examples of the Town lattice truss include “Brown Bridge,” HAER No. VT-28 and 

“Roseman Bridge,” HAER No. IA-95. Additional examples of this truss type are listed in the appendix.

32 Lawrence P. Grayson, The Making of an Engineer: An Illustrated History of Engineering Education in 

the United States and Canada (New York: John Wiley and Sons, 1993), 24.

33 S. H. Long, U.S. Patent No. 5,862X, March 6, 1830. In most Long-truss bridges, the struts above the 

upper chords and below the lower chords were eliminated.

34 S. H. Long, Description of Col. Long’s Bridges, Together With a Series of Directions to Bridge Builders

(Concord, N.H.: John F. Brown Printers, 1836), 42.

35 Noteworthy examples of the Long truss include “Eldean Bridge,” HAER No. OH-122 and “Blenheim 

Bridge,” HAER No. NY-331. The latter bridge was destroyed by floods that followed Hurricane Irene 

in 2011. Additional examples of this truss type are listed in the appendix.

36 Noteworthy examples of the Paddleford truss include “Sunday River Bridge,” HAER No. ME-69 and 

“Mechanic Street Bridge,” HAER No. NH-45. Additional examples of this truss type are listed in the 

appendix.

37 The Quaboag River Bridge was replaced in 1873 with a larger Howe-truss covered bridge capable 

of carrying two tracks. The Western Railroad Bridge (which was left uncovered) was replaced with a 

covered bridge in 1855.

38 William Howe, U.S. Patent No. 1,711, August 3, 1840. Howe received another patent in 1846 and a 

reissue in 1850, but the design of most Howe-truss bridges was simplified from the patent drawings.

39 Victor C. Darnell, A Directory of American Bridge Building Companies, 1840–1900 (Washington, D. 

C.: Society for Industrial Archeology, 1984), 25–26.

40 “Bridge Superstructure,” Transactions of the American Society of Civil Engineers (1878), 340.

41 Noteworthy examples of the Howe truss include “Pine Bluff Bridge,” HAER No. IN-103 and “Knight’s 

Ferry Bridge,” HAER No. CA-314. Additional examples of this truss type are listed in the appendix.

42 Thomas W. Pratt and Caleb Pratt, U.S. Patent No. 3,523, April 4, 1844.

43 “Pratt, Thomas Willis,” in Dictionary of American Biography, vol. 8 (New York: Charles Scribner’s Sons, 1933), 

179.

44 See “Sulphite Railroad Bridge,” HAER No. NH-36 and “Honey Run Bridge,” HAER No. CA-312. 

See also Joseph D. Conwill, “Wood Copies Steel: the Modified Pratt Truss,” Covered Bridge Topics 52, 

no. 4 (Fall 1994): 10.

45 Joseph D. Conwill, “The Red Covered Bridge: Fiction Affects Fact,” unpublished typescript, July 26, 2004.

Endnotes
74 Covered Bridges and the Birth of American Engineering

46 Snyder Brook Bridge (1918) in Coos County, New Hampshire, is one of five surviving boxed pony 

truss bridges in the United States; see “Snyder Brook Bridge,” HAER No. NH-49. Harpole Bridge 

(1922) in Whitman County, Washington, is the only surviving boxed through-truss bridge in the 

United States; see “Harpole Bridge,” HAER No. WA-133. Sulphite Railroad Bridge in Merrimack 

County, New Hampshire, is the only surviving deck-truss covered bridge in the United States; see 

“Sulphite Railroad Bridge,” HAER No. NH-36.

47 There are widely scattered examples of non-housed timber-truss bridges across the United States and 

significant numbers are still in use in Canada.

48 See “Dunlap’s Creek Bridge,” HAER No. PA-72. Dunlap’s Creek Bridge has been widened but is still 

in service.

49 David A. Simmons, “Fall From Grace: Amasa Stone and the Ashtabula Bridge Collapse,” Timeline 6, 

no. 3 (June–July 1989): 34

50 Some areas of the country still had a reasonable supply of local timber, while others imported it from 

timber-rich regions. In some places, a strong local tradition and/or the presence of a prominent bridge 

builder kept covered bridge building competitive into the late nineteenth and early twentieth centuries.

51 Squire Whipple, An Essay on Bridge Building (Utica, N.Y.: by the author, 1847).

52 Robert W. Smith, U.S. Patent No. 66,900, July 16, 1867.

53 Noteworthy examples of the Smith truss include “Powder Works Bridge,” HAER No. CA-313 and 

“Cataract Falls Bridge,” HAER No. IN-104. Additional examples of this truss type are listed in the 

appendix. Also see “Structural Study of Smith Trusses,” HAER No. PA-645.

54 Robert W. Smith, U.S. Patent No. 97,714, December 7, 1869. In 1967, industrial engineer and coveredbridge enthusiast Raymond E. Wilson of Swarthmore, Pennsylvania, established a classification of 

Smith-truss variations, based on the number and configuration of the web members. Type 1 follows 

the drawing shown in the 1867 patent. Type 2 follows the drawing shown in the 1869 patent. Type 3 is 

similar to type 2 but with extra braces in the center panel. Type 4 has double inclined posts and single 

braces the full length of the truss. Wilson’s taxonomy is still in use today; however, it is considered by 

some scholars to be overly simplistic, primarily because it fails to account for a primary innovation 

addressed in Smith’s first patent: increasing the number of web planes as span length is increased. See 

also discussion in chapter 5. Raymond E. Wilson, “The Story of the Smith Truss,” Covered Bridge 

Topics 25, no. 1 (April 1967): 3–5; Matthew Reckard, “Robert Smith’s Trusses,” Second National 

Covered Bridges Conference, Dayton, Ohio, June 5–9, 2013, http://www.woodcenter.org/docs/daytonconference/Reckard_Smith’s%20Trusses.pdf.

55 Isaac H. Wheeler, U.S. Patent No. 107,576, September 20, 1870. One Wheeler-truss bridge survives in 

Kentucky, but it was substantially rebuilt in 2004; see “Bennett’s Mill Bridge,” HAER No. KY-49.

56 Reuben L. Partridge, U.S. Patent No. 127,791, June 11, 1872. Five examples of the Partridge truss survive 

in Ohio, including “Pottersburg Bridge,” HAER No. OH-125.

57 Hundreds of these backyard and folk-art bridges can be found throughout the United States. Arthur F. 

Hammer, ed., Romantic Shelters: A Supplement to the World Guide to Covered Bridges (Marlboro, Mass.: 

National Society for the Preservation of Covered Bridges, 1989).

58 Arson is a major challenge to covered bridge preservation. Since the 1950s, nearly 200 covered bridges 

have been deliberately set on fire. On average, between two and five covered bridges are lost annually to 

arson.

59 Oregon State Highway Commission, Second Annual Report of the Engineer of the Oregon State 

Highway Commission for the year ending November 30, 1915, 53.

Endnotes
History of Covered Bridges in the United States 75

60 Some of the single-stick chords found in Oregon covered bridges are of impressive dimensions. Pengra 

Bridge (1938) in Lane County has bottom chords measuring 16 inches x 18 inches x 126 feet. See 

“Pengra Bridge,” HAER No. OR-119.

61 Nick Cockrell and Bill Cockrell, Roofs Over Rivers: A Guide to Oregon’s Covered Bridges (Beaverton, 

Ore.: Touchstone Press, 1978), 103. Many of those covered bridges were lost in the latter half of the 

twentieth century. Today, approximately forty covered bridges built during the historic era of covered 

bridge building survive in Oregon.

62 Joseph D. Conwill, Covered Bridges Across North America (St. Paul, Minn.: MBI Pub. Co., 2004), 

77. Irish Bend Bridge (1954) in Benton County, Oregon, is generally considered to be the last covered 

bridge built during the historic era of covered bridge building. The structure was bypassed in the 1970s 

and moved to the Oregon State University campus at Corvallis in 1989.

63 See “Hancock-Greenfield Bridge,” HAER No. NH-42.

64 Milton S. Graton, The Last of the Covered Bridge Builders (Plymouth, N.H.: Clifford-Nicol, Inc., 1978), 

79–108; Conwill, Covered Bridges Across North America, 108–10.

65 Approximately 80 percent of the nation’s extant covered bridges built during the historic era of covered 

bridge building are located in six states: Pennsylvania (27 percent), Ohio (17 percent), Indiana (13 

percent), Vermont (11 percent), New Hampshire (6 percent), and Oregon (6 percent).

Endnotes

77

Chapter 4

The Engineering Design

of Covered Bridges

by Dario Gasparini, Rachel H. Sangree, and James Barker; 

edited by David A. Simmons and Michael R. Harrison

The Engineering Design of Covered Bridges

Covered bridges are, indeed, wonderful examples of craftsmanship, but they should also 

be appreciated as engineered structures. Engineers have historically contributed to their 

development, especially to their safety and reliability. In fact, the demand for reliable 

covered bridges was a driving force in the growth of the American engineering profession in 

the 1830s and 1840s. This chapter explores concepts and principles used in the engineering 

design of covered bridges in order to enhance understanding and appreciation of these iconic 

American structures. 

The general objective of covered bridge design is to provide a cost-effective, functional, safe, and 

durable crossing. The siting of the bridge and the locations of piers and abutments are critical 

decisions of primary importance. These essential foundation components must be safe during 

extreme floods. The overall geometry of a bridge and its approaches must provide for a safe 

crossing. A wooden bridge must be protected from fire, water, and biological degradation to achieve 

durability. And, importantly, a wooden structure must be conceptualized and detailed to resist a 

variety of loads. It is this process of structural design that is the focus of this chapter. Structural 

design is based on the application of several important mathematical and physical concepts. 

Basic Engineering Concepts 

For most of human history, structures have been built on the basis of experiment and observation, 

or, it is said, empirically. This means that builders used “traditional proportions” established over 

time from observation of successful existing structures. Alternatively, for some simple structures, 

small-scale physical models were built in an attempt to infer the strength and stability of full-scale 

structures. James Finley, for example, successfully built suspension bridges in early-nineteenthcentury Pennsylvania based on his observations of small-scale models.1 Similarly, small-scale 

models of stone arches were built to identify potential failure mechanisms of actual arches. In 

general, however, it is difficult to construct appropriate small-scale physical models from which 

reliable predictions of forces may be made. Although many of mankind’s celebrated structures 

were built empirically, such a design process is now understood to have a clear drawback: the 

safety of designs conceptualized in response to new uses or improved materials is difficult to 

verify prior to building the actual structure. Therefore, an empirical design process generally 
78 Covered Bridges and the Birth of American Engineering

involves higher risk and expense. An alternative, called the engineering design method, emerged 

in the early nineteenth century. This new method was made possible by a centuries-long gradual 

understanding of significant engineering concepts as well as through the transformative work 

by French engineer Claude-Louis-Marie-Henri Navier in the 1820s. 

The essential concepts for structural design are those of force, moment of a force, and equilibrium; 

elasticity and strength of materials; and geometric compatibility between member deformations 

and joint movements in a structure, described in further detail below.

Force, moment of a force,and 

force equilibrium — The concept 

of force developed from observation 

of natural phenomena, including 

the weights of objects, the action 

of simple mechanisms such as the 

lever, the fluid effect of buoyancy, 

the existence of friction, and the 

motion of bodies. Isaac Newton 

defined a force as the causative 

action for a change in momentum 

of an object or for an acceleration 

of a mass. Acceleration has an 

associated direction and its causative action, the force, must have the same direction. A force is, 

therefore, a quantity that has both size, or magnitude, and a direction. Such a quantity may be 

defined using the mathematical concept of a vector and may be depicted by an arrow as shown 

in figure 4.1a. The direction of a force in a plane may be defined by an angle, a, with respect to a 

reference axis and the tip of the arrow. The length of the arrow represents the size, or magnitude. 

Force magnitudes are given as multiples of standard units such as the pound (lb), or the Newton (N). 

Figure 4.1 Forces having magnitude and direction can be represented by

vectors. In figure 1a, the force has a component in the Y direction and a component in the X direction. Figure 1b is a vector representation of the weight of 

a 150-lb person acting in a downward direction. In covered bridges, axial forces 

are tensile or compressive, depicted in figure 1c. Unless otherwise noted, all 

diagrams in this chapter were drawn by Dario Gasparini and Pavel Gorokhov.

 

 

 

 

 

 

 

 

 

 

 

 

In the context of covered bridge trusses, the primary forces in the members are generally aligned 

with the longitudinal axes of the members. Such axial forces are said to be tensile or compressive, 

as shown in figure 4.1c. 

A body in a plane can have acceleration in the 

vertical and horizontal directions as well as rotational

acceleration about an axis perpendicular to the plane 

of the body. A simple example is the rotation of a 

wheel about its axle. The causative action for rotational 

acceleration is called the moment of a force or simply 

the moment. The magnitude of the moment of a planar 

force about an axis perpendicular to its plane equals 

the force magnitude multiplied by the perpendicular 

distance from the line of action of the force to the 

axis (figure 4.2). 

Figure 4.2 The action of loosening a bolt with a wrench

is an example of the moment of a force. In this case, the 

moment of the 20-pound force about the point, or axis, 

0 is 20 pounds x 12 inches = 240 pounds-inch.
The Engineering Design of Covered Bridges 79

Objects not accelerating nor at rest can have forces acting on them, but the net or resultant forces must 

be zero. When this is the case, the body is said to be in equilibrium. A two-dimensional or planar 

structure, such as a bridge truss, must satisfy three independent equilibrium requirements in order to 

remain at rest: the sum of the forces in the horizontal direction must be zero; the sum of the forces in 

the vertical direction must be zero; and the sum of the moments about any axis perpendicular to its 

plane must also be zero (figure 4.3). 

Figure 4.3 This two-member truss demonstrates equilibrium. The truss shown is subject to a horizontal force of 1,000 pounds 

and a vertical force of 2,000 pounds acting at joint b. Since the truss is at rest, the reactive forces at supports a and c must be such 

that the resultant force in the horizontal direction on the entire truss is zero, and, independently, the resultant force in the vertical 

direction must also be zero. The member axial forces, N1 and N2, may be determined by invoking equilibrium at joint b.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

This equilibrium requirement also applies to any discrete part of a structure as well as to points 

on a structure. The method of joints, whereby engineers isolate each joint in a truss and calculate 

the forces acting on those points, is a fundamental application of equilibrium principles in both 

structural engineering generally and bridge design specifically.

Elasticity and strength of materials — All materials and structural members deform when 

forces are applied. This is evident when stretching a rubber band or when compressing a spring. 

In 1678, Robert Hooke made the important observation that for many materials the deformation 

is linearly proportional to the applied force. Figure 4.4 shows a specimen with an initial length L and 

cross-sectional area A subjected to an applied axial tensile force N. The force or load divided by the 

cross-sectional area is called stress, and the elongation e divided by the initial length is called strain. 

For many materials the strain is linearly proportional to the stress. The slope of the stress-strain 

curve, denoted by E, is called the modulus of elasticity, or Young’s modulus.

2 The term linear elastic 

is used to define a material whose stress-strain behavior is linear and that has an unloading curve 

that coincides with its loading curve.

In the experiment illustrated in figure 4.4, the applied stress may be increased until the material 

ruptures or fails. The magnitude of the stress that causes rupture is called the strength of the material. 

A basic criterion of structural design is that the stresses in completed structures should be well below 

the strengths of the materials used.
80 Covered Bridges and the Birth of American Engineering

 

 

 

 

 

 

 

 

 

 

Figure 4.4 Left: 4.4a) represents a tensile test to determine 

the mechanical properties of 

material; the force N divided by 

cross-sectional area A is called 

stress, while the amount of 

elongation (e) divided by the 

original length(L) is called strain. 

Right: 4.4b) is a graph representing linear stress-strain behavior 

where E defines the modulus 

of elasticity of a material. 

Geometrically compatible member axial deformations and joint movements — Another 

independent concept used in engineering design is that the deformations of members of a structure 

must be geometrically consistent, or compatible, with the movements or displacements at various 

points in a structure. Geometric compatibility requirements were studied extensively in the eighteenth 

century, primarily in the context of calculating work done by forces.3 Equations stating geometric 

compatibility requirements depend on whether the movements of a structure are small or large. 

Commonly, the movements that occur when loads 

are applied to a structure are small relative to the 

structure’s dimensions. For these common cases, 

the compatibility equations are linear, and the 

structure is said to be geometrically linear. The 

nature of geometric compatibility equations may 

be illustrated by considering the two-member truss 

in figure 4.5. The applied loads cause changes in 

member lengths, or axial deformations, denoted 

by e1

 and e2. These deformations, in turn, produce 

movements, or displacements, of joint b, denoted as 

u and v. The member axial deformations and the 

joint displacements must satisfy two linear equations 

derived from geometry in order to be compatible.

 

 

 

 

 

 

 

 

 

 

 

 

Figure 4.5 Applied loads cause changes in member 

lengths and movements of joint b, denoted by u and v.

The dashed lines indicate the displaced position of

the truss.

By the end of the eighteenth century, the concepts of force equilibrium, linear elasticity, and 

geometric compatibility had been known for over 100 years. But a method for using these three 

independent requirements to predict the effects of loads on structures had not been defined. Such 

a synthesis occurred early in the nineteenth century and was largely the work of one individual, 

Claude-Louis-Marie-Henri Navier.

The Transformative Work of Navier

Claude-Louis Navier (1785–1836) was a professor at the École Nationale des Ponts et Chaussées in Paris, 

the pre-eminent engineering school of the time. He first published his lectures in an 1826 book titled 

Résumé des leçons that included extensive data on the mechanical properties of materials, important 
The Engineering Design of Covered Bridges 81

theoretical developments on beams and trusses, and discussions of 

specific designs. Navier assembled experimental data from a variety of 

leading European engineers, including Jean Rondelet, John Rennie, 

Thomas Tredgold, Jean-Rodolphe Perronet, Giovanni Poleni, Marc 

Seguin, Jean-Marie-Constant Duhamel, Thomas Telford, Georges 

Louis Leclerc Buffon, William Henry Barlow, and Guillaume Henri 

Dufour. Navier’s book contained data on the modulus of elasticity of 

stone, brick, cast iron, wrought iron, iron wire, and wood, including 

“le pin d’Amerique [American pine].” In addition, Navier considered 

strengths of members, specifically beams and columns, where buckling 

was an important consideration, and proposed allowable stresses for 

various materials.

Figure 4.6 Bust of Claude-LouisMarie- Henri Navier, sculpted by 

Henri Cros in 1885. Courtesy of École 

Nationale des Ponts et Chaussées.

Navier’s theoretical developments focused on the theory of 

beams and the theory of trusses. In the context of trusses, 

he gave explicit solutions for forces in the members of an 

asymmetric kingpost truss subject to a vertical load as 

shown in figure 4.7. He determined the effects of the load 

through a process now known as structural analysis. The 

simple kingpost truss is said to be statically determinate

because the forces in the members may be determined using 

only equilibrium equations. The significance of Navier’s 

solution, together with knowledge of member strength, 

was that an engineer could size wood members in such a way that stresses were at allowable values, 

well below strength levels. The structural analysis process moved structural design practice away 

from empirical methods. By 1826, an engineer could reliably size the members of a kingpost truss 

for any span and load. 

Figure 4.7 An asymmetrical kingpost truss 

studied by Navier.

Furthermore, Navier derived an explicit solution for 

the forces and displacements of the three-member truss 

shown in figure 4.8. This truss was significant because it 

was statically indeterminate; its member forces could not 

be determined using only equilibrium equations. Navier 

combined the three conditions of force equilibrium, linear 

elasticity, and geometric compatibility to arrive at a set 

of equations that could be solved for the joint displacements and member forces. It is said that 

Navier defined a mathematical model of the truss in the sense that the set of equations modeled 

the mechanical behavior of the actual truss. Navier’s formulation required solving a set of two 

simultaneous linear algebraic equations, a task easily done manually, and it was almost surely the 

first linear elastic structural analysis of a statically indeterminate structure. But, as the number of 

joints in a truss increased, the number of simultaneous linear algebraic equations quickly increased 

to the point where a manual solution became impractical. Therefore, the full power of Navier’s 

formulation was not realized until the late 1950s or early 1960s, when computer programs for 

structural analysis were first developed.

Figure 4.8 A statically indeterminate threemember truss studie by Navier
82 Covered Bridges and the Birth of American Engineering

Navier’s most influential contribution to 

wooden-truss bridge design came from 

his observation that a parallel chord truss 

stiffened by diagonals functioned effectively 

as a beam. The calculations builders used to 

determine stresses in beams could therefore 

be adapted to ascertain the maximum forces 

in the chords of single-span trusses. He 

determined that the stiffness of a parallel 

chord truss was proportional to the area of 

the chords multiplied by the square of the 

distance between them. This observation 

enabled engineers to safely size the chords in 

parallel-chord trusses for any span and load, 

as depicted in figure 4.9.4 

 

 

 

 

 

Figure 4.9 Navier observed that 

the forces in a parallel chord truss 

(whose cross-sectional dimensions 

are defined in figure 4.9b) may be

calculated using beam theory, a

methodology he devised. He proved that the stiffness of such a truss 

was proportional to the area of the 

chords multiplied by the square 

of the distance between them.

Navier’s contributions to structural analysis transformed structural design itself. His work enabled 

engineers to define mathematical models of structures, to compute the effects of loads, and, together 

with data on material and member strength, to size members by limiting stresses to safe, allowable 

values. Navier’s paradigm is still used in structural design today.

Navier’s advances were transferred to America very quickly. A young engineer named Stephen 

Harriman Long, who graduated from Dartmouth College in 1809, published an article in The Port 

Folio in 1825 that cited Navier as well as Jean-Nicholas-Pierre Hachette’s Traite elementaire des 

machines, demonstrating that Long had read the most recent developments in French engineering 

science.5 In 1829, Long sized the chords of the wooden-truss Jackson Bridge, carrying the 

Washington Road over the Baltimore and Ohio Railroad, using Navier’s beam analogy, almost 

surely the first American use of this new development. Long’s truss design for this bridge, which 

he patented in 1830, was quickly and widely adopted.6

Long published a booklet in 1830 describing the Jackson Bridge and giving instructions to builders 

using his patent. He revised these instructions in 1836 when he published another booklet describing 

his patent in greater detail. The latter contained remarkable tables providing truss depths and crosssectional areas of all members for twenty spans ranging from 55 feet to 300 feet. The areas of the 

chords in Long’s book were consistent with Navier’s analysis of a parallel-chord truss as a beam, 

showing that Long understood and applied Navier’s theories.7

Instructors at West Point used French engineering education as their model. It is likely Navier’s 

lectures were known at West Point shortly after their 1826 publication, if not before. Dennis Hart 

Mahan graduated first in his class from West Point in 1824 and became an assistant professor at the 

academy that same year. In 1826, he sailed for France to study at the military school for engineers 

and artillerists at Metz. He returned to teach at West Point in 1830 and remained there his entire 

life.8

 Mahan included many of Navier’s ideas in his 1837 textbook, An Elementary Course of Civil 

Engineering for the Use of the Cadets of the United States Military Academy. Mahan commented in 
The Engineering Design of Covered Bridges 83

the book’s introduction that Navier’s name “is connected, either as author or editor, with the ablest 

works on the subject under consideration that have appeared in France within the last twenty years; 

and the best counsel that the author could give to every young engineer is to place in his library 

every work of science to which M. Navier’s name is in any way attached.” The mechanics portion 

of Mahan’s text considered many of the same examples and provided the same solutions as those 

found in Navier’s Résumé des leçons. Specifically, Mahan gave the solution for the forces in a kingpost 

truss and stated Navier’s analogy of a parallel-chord truss as a beam, actually using one of Navier’s 

figures. Mahan did not repeat Navier’s analysis of a statically indeterminate truss, perhaps because he 

recognized the practical limitations of applying Navier’s formulas to trusses with many more joints.9

Although Navier did permanently change the way engineers designed structures, his work was 

only a start. There has since been a continuous line of contributions to mathematical modeling of 

structures and understanding of structural behavior, progress in structural engineering knowledge 

that continues today. In addition, it should be emphasized that Navier’s contributions were primarily 

in structural analysis, which is only one step in the structural design process.

Structural Design of Bridges

The bridge design process has evolved over time but there are basic design considerations that have 

remained the same. The design process begins by prescribing functionality requirements that set 

the width, span, clearances, abutment elevations, and other geometric features. Design loads must 

then be defined, which normally include the estimated self-weight, or, in engineering usage, dead 

load, and transient, or live, loads, such as people, vehicles, snow, and wind. (It should be noted 

that wind causes primarily horizontal, or lateral, forces on the sides of a covered bridge.) Selecting 

the magnitudes of design live loads can be a source of conflict or disagreement among participants 

because of the uncertainty in the actual load magnitudes that may occur and the tradeoff between 

design loads and the cost of a bridge. In general, the larger the design loads the greater the cost of 

a bridge. Engineers refer to larger loads, which are less likely to occur, as being more conservative. 

Current design load magnitudes are generally prescribed by legal documents, or codes, but these 

standard loads were only defined in the United States beginning in the late 1870s. 

The next step in the design process is to conceptualize a structural system that can safely carry the 

design loads. This includes a floor system, a system for lateral loads, and the principal trusses for the 

dead and live gravity loads. Because of their primary responsibility for safety, engineers generally do 

not favor conceptual designs that are inconsistent with their understanding of structural behavior 

or that are difficult to model mathematically. This may explain why Navier barely referenced the 

famous—and complex—European covered bridges at Schaffhausen and Wettingen and why he never 

discussed the very successful and widely used Town and Burr designs, which were surely known to 

him. As part of the conceptual design, suitable materials must also be selected. Structural design 

then generally enters a cyclic, or iterative, process of mathematical modeling of the structure and 

loads, structural analysis to determine the effects of the loads, and checks on whether acceptance 

criteria on strength, stiffness, and stability are met. Concurrently, the all-important connections 

must be designed and detailed. Each of these steps involves concepts that shed light on engineering 

structural design and therefore are described in more detail in the following sections. 
84 Covered Bridges and the Birth of American Engineering

Selecting Design Loads

Pioneering builders of covered bridges, like Timothy Palmer, Lewis Wernwag, and Theodore Burr, 

did not know the superimposed loads that their bridges could safely carry because mathematical 

techniques for predicting the effects of loads had not been developed. With the introduction of 

structural analysis techniques in the late 1820s, engineers were able to define explicit design loads 

and to size members to safely carry the effects of these loads.

Covered bridges, of course, have to be able to support their own weight, called the dead load. Estimating 

dead load is a simple but critical and laborious task that requires calculating the volumes of the various 

materials in the bridge and then multiplying the volumes by their corresponding unit weights. A much 

more challenging task is to define imposed or moving loads, called live loads. Depending on the type of 

covered bridge, moving loads could include pedestrians, livestock, carriages, freight wagons, or trains. 

Engineers assumed such loads primarily caused downward, gravitational forces. Other actions normally 

considered in structural design were wind-induced pressures and snow loads. Although earthquakes are 

typically considered today, nineteenth-century engineers thought of them as “acts of God,” along with 

extreme floods, and did not expect the structures to survive without significant damage or even collapse.

Wagons, animals, and pedestrians crossing covered bridges moved too slowly to cause significant 

acceleration responses, so nineteenth-century engineers treated such loads as static rather than 

dynamic, even though they represented people or vehicles in motion. Engineers of that era also 

ignored forces created by changing temperatures (thermal forces), as the coefficient of thermal 

expansion for wood parallel to its grain was so low. In modeling static loads, engineers needed to 

decide whether the loads acted as a concentrated force at a single point on a bridge, or as a distributed 

force over a given area, as shown in figure 4.10. For example, even though individuals in a crowd 

cause gravity forces at their specific locations, the entire crowd is generally regarded as a uniformly 

distributed load over a particular area. 

 

 

 

 

 

 

 

 

 

 

 

Figure 4.10 Typical bridge floor framing is shown with concentrated loads, 

distributed loads, and contributing area. 

A distributed load is usually allocated to 

specific members using the geometric 

concept of contributing area. In this 

example, crossbeam 2 in the diagram is 

assumed to carry the entire distributed 

load over the contributing area defined 

by points a-b-c-d.

Another important decision that engineers had to make when selecting design loads was where 

along a span to place a heavy concentrated load, such as a heavily-loaded wagon or the engine of a 

train. This decision required predicting the effects of the concentrated load in all members for all the 

possible positions of the load. In general, a load position that caused the greatest effect, or force, in 

one member was different from the load position that caused the greatest effect in another member. 

An even more fundamental judgment required deciding which loads should be assumed to act 

concurrently, or in combination. For example, it is intuitive that the dead load should always 

be included in combination with a live load. But should wind-induced forces be assumed to act 
The Engineering Design of Covered Bridges 85

concurrently with distributed live loads, given that each design magnitude had a low probability 

of occurrence? These assumptions are now largely prescribed by design codes—which did not exist 

in the early nineteenth century—but initially required engineering judgment. 

The last step in modeling a load was the all-important decision on the magnitude to be used. Large, 

very conservative magnitudes resulted in designs that were safer but could entail costs that were 

excessive. Conservative thinking on loads was intimately related not only to safety but also to cost. 

Engineers generally defined load magnitudes that were well above average, although the actual 

probability of exceeding them was unknown. Today, engineers call such design loads working loads. 

Some of the issues involved in the evolution of load modeling are illustrated with a review of the 

early development of design live loads for suspension bridges, specifically the work by Navier on 

defining design loads for the Pont des Invalides, a suspension bridge over the River Seine. His 1823 

report on theoretical developments related to suspension bridges included a detailed description of 

his logic for defining uniformly distributed design live loads.10 He considered three load scenarios:

1. an orderly crowd of men, women, and children modeled as three 65-kilogram

 persons per square meter, or a uniformly distributed live load of 195 kg/m2

;

2. a cavalry troop traversing the span, a load he estimated to be 130 kg/m2

 by considering the actual weights of horses and cavalrymen and the areas they occupied; and

3. two lines of wagons carrying building stones, each weighing 8,400 kg and pulled by 

four horses, which also produced a uniformly distributed load smaller than that 

caused by a crowd. (He recognized that heavier wagons existed but stated that it was 

unlikely to have two lines of such wagons on the span simultaneously.)

Based on these three scenarios, Navier designed the bridge to support a uniformly distributed live load 

of 195 kg/m2

 (40 lb/ft2). In 1826, Guillaume Henri Dufour and Marc Seguin, two pioneering French 

suspension bridge designers who also had to make decisions on design live loads, commented on Navier’s 

logic and decision. Dufour stated that such a load seemed unnecessary “except for small bridges . . . 

and for those large bridges in very populous capital cities . . . everywhere else probability should govern 

decisions so as not to succumb to exaggerated expense.” Dufour explicitly stated that loads were random

and recommended that designers decide on loads that had an acceptable and consistent probability that 

they would not be exceeded. Dufour understood that the probability of having a uniform load of 195kg/

m2

 over the entire area of a small bridge in an urban setting was much greater than the probability of 

having the same load over the entire area of a large bridge in a rural setting, and he consequently objected 

to using the same design load in both cases. Marc Seguin, who echoed Dufour’s thoughts, reduced his 

live load estimate to 183 kg/m2

 for his famous Tournon-Tain suspension bridge, while Dufour used an 

even lower distributed live load of 154 kg/m2

 for his Saint Antoine Bridge.11

British engineers deduced their own design live loads. Thomas Telford used an effective distributed 

load of only 54 kg/m2

, or 11 lb/ft2, for his renowned Menai Straits Bridge of 1826, but other British 

engineers, whose logic is unknown, typically used a live load of 70 lb/ft2

, which was considerably 

greater than Navier’s.12
86 Covered Bridges and the Birth of American Engineering

Stephen Long was likely the first American covered bridge builder to explicitly state a design live 

load. He used a live load of 120 lb/ft2

 in his 1836 booklet to compute axial stresses in bridge chords. 

He proportioned chord areas so that the maximum chord stresses were one-half of the minimum 

wood strength (assumed to be 4,000 psi). Long apparently computed this design load, three times 

Navier’s load, using the weight of two trains on a bridge. Although Long used very large, uniformly 

distributed live loads, he “allowed” relatively high axial stresses, equal to one-half of his assumed 

minimum compressive wood strength.13

D. H. Mahan’s 1837 book provided no guidelines for design live loads. Influential New York 

engineer Squire Whipple felt it proper to consider “the whole area of the roadway, covered with men, 

which is about 100 lbs. to the square foot, as the greatest load to which the bridge can be exposed.” 

Herman Haupt stated without explanation that “the greatest variable load is generally considered 

as caused by a crowd of people, and is estimated at 120 lbs. per square foot.”14 Such a load seems 

to have been a maximum live load used by early engineers for road bridges. 

By 1888, American engineer J. A. L. Waddell recommended a more measured approach, as illustrated 

by table 1. Waddell defined three classes of “ordinary” highway bridges. “Class A” included urban 

bridges with continuous heavy loads; “Class B” comprised urban bridges with occasional heavy loads; 

and “Class C” included country road bridges. In addition, Waddell defined live loads for joists, floor 

beams, beam hangers, and hip verticals as “one hundred (100) pounds per square foot for bridges of 

Classes A and B, and eighty (80) pounds per square foot for Class C.” Waddell’s categorization of 

bridges and distinction between bridges of different lengths (and different surface areas) reflected the 

assessment made by Dufour and Seguin. He thought that the loadings on larger bridges and those in 

rural areas could be reduced without fear that they would be exceeded under ordinary circumstances.15

Span in feet

Moving load per square foot of floor

Class A Class B Class C Class D

0 to 50 100 100 80 65

50 to 100 100 95 80 60

100 to 150 95 90 75 55

150 to 175 90 85 75 50

175 to 200 85 80 70 ---

200 to 225 80 75 65 ---

225 to 250 75 70 60 ---

250 to 275 70 65 55 ---

275 to 300 65 60 50 ---

300 to 350 65 55 45 ---

350 and over 65 55 40 ---

Table 1: Waddell’s uniformly distributed live loads for bridges, from J. A. L. Waddell, General Specifications for Highway Bridges of 

Iron and Steel, 2d ed., page 25.
The Engineering Design of Covered Bridges 87

 In northern climates, engineers also designed for the imposed weight of snow. The main questions 

regarding snow were its unit weight, the accumulated depth, and variations due to the pitch, or 

slope, of various roof surfaces. John C. Trautwine measured snow unit weights and performed 

experiments with snow accumulation on a variety of roof surfaces and slopes, publishing the 

results in the 1872 first edition of The Civil Engineers’ Pocket-Book. His trials “showed the wt. of 

freshly fallen snow to vary from about 5 to 12 lbs per cub. ft.; apparently depending chiefly upon 

the degree of humidity of the air through which it had passed.” In the United States, he suggested, 

“the allowance for snow should not be taken at less than 12 lbs; or the total for snow and wind, 

at 20 lbs.” The 1904 edition of the Pocket-Book noted, “The snow load, in States north of lat. 35°, 

may be taken as varying (chiefly with latitude) from 10 to 30 lbs. per sq. ft. of horizontal projection 

of roof surface.” Today, engineers still use the concept that snow load is applied to the horizontal 

projection of a roof.16

The steady evolution toward bridge design specifications that began in the early nineteenth century 

with wooden trusses reached its culmination in the third quarter of the century through the design 

of iron railroad bridges. For railroad bridges, the principal loading was obviously not from crowds 

or snow but from the weights of the engines, tenders, and loaded cars. Their dramatic increase from 

the 1830s through the nineteenth century made it essential to prescribe safe loads as part of the 

bridge design specifications. In the early 1870s, various bridge companies, such as the Phoenix Iron 

and Bridge Works, began specifying bridge capacities. Important changes in the definition of train 

design loads originated with Louis Bouscaren’s 1875 specifications for the Newport and Cincinnati 

Bridge over the Ohio River of the Cincinnati Southern Railway, as shown in figure 4.11.17

Figure 4.11 The specifications for the Newport and Cincinnati Bridge designed by Louis Bouscaren for the Cincinnati 

Southern Railway and completed in 1877 were instrumental in establishing national bridge design standards. From Illustrated 

Business Directory and Picturesque Cincinnati, 1883 (Cincinnati, Ohio: Spencer & Craig Printing Works, 1883), 76. Courtesy of Ohio 

History Connection.
88 Covered Bridges and the Birth of American Engineering

About this time, engineers recognized that rapidly moving trains caused some acceleration responses 

and inertia forces in a bridge. A train could be a dynamic rather than a static load, requiring the 

addition, in Bouscaren’s terms, of “ten to thirty percent” to the stresses computed from static load 

and bridge models. Called an impact factor, it and Bouscaren’s prescribed axle loads (figure 4.12) 

became permanent changes in bridge specifications still used to this day. 

Figure 4.12 Bouscaren prescribed for the first time that a train must be modeled as a set of moving axle point loads, here given 

in tons. Engineers had to consider all possible positions of the point loads in order to determine the greatest effect (force) in each 

member. Adapted from Thomas Lovett, Report on the Progress of Work, Cost of, Etc., of the Cincinnati Southern Railway (Cincinnati, 

Ohio: Wrightson & Co., Printers, 1875), 25.

The collapse of the all-iron Howe-truss railroad bridge at Ashtabula, Ohio, on December 29, 1876, 

accelerated the process of developing “model” or national specifications, especially for railroad 

bridges. Perhaps the most widely adopted specifications in America were those written by Theodore 

Cooper, an early version of which appeared in Engineering News in 1879. Cooper’s specifications 

followed Bouscaren’s lead in requiring a moving axle load model for trains.18

The forces induced on bridges by strong winds were less understood and more difficult to model. 

Navier’s 1826 Leçons gave no guidelines on wind; he merely stated that wind forces and their effects 

could not be accurately predicted. As wind blows over a bridge, it creates pressures perpendicular 

to surfaces that vary from point to point depending on the shape of the bridge, the direction of the 

wind, and the wind’s turbulence. Nevertheless, the overall stability of a bridge generally depends 

Figure 4.13 Amasa Stone was a highly 

accomplished railroad contractor of 

traditional combination wood and iron 

Howe trusses. After building several 

Howe trusses with cast-iron webs, he 

experimented with a Howe design that 

substituted wrought-iron I-beams for 

the wooden diagonals. Completed in 

1865, the Ashtabula Bridge collapsed 

during a blizzard in December 1876, 

resulting in one of the nation’s deadliest 

bridge disasters. A broken cast-iron 

bearing block was identified as the 

immediate cause of the collapse. 

Thomas T. Sweeny, photographer, 1865. 

Courtesy of Ohio History Connection.
The Engineering Design of Covered Bridges 89

on some average pressure over the entire exposed surface of the structure, not on peak pressures at 

a few locations. The main discussion in the nineteenth century focused on determining reasonable 

values for this average pressure that could be used in designing bridges and checking their stability.

John Smeaton’s An Experimental Enquiry Concerning the Natural Powers of Water and Wind to 

Turn Mills, published in 1760, and Julius Weisbach’s Principles of the Mechanics of Machinery 

and Engineering, first published in an American edition in 1848, were the two principal scientific 

references on fluid pressures used by nineteenth-century structural engineers. Smeaton’s publication 

contained a table that correlated wind velocity to wind pressure. Smeaton’s data went as high as 

100 mph, as shown in table 2. Because such velocities seemed extreme, bridge engineers typically 

used design wind pressures between 30 lb/ft2

 and 50 lb/ft2.

19

Wind velocity (mph) Wind pressure (psf) “Common appellations of the 

 force of winds.”

30 4.429 “High winds.”

40 7.873 “Very high.”

50 12.3 “A storm or tempest.”

60 17.715 “A great storm.”

80 31.490 “An hurricane.”

Table 2: Selected wind velocities with their corresponding wind pressures as given by John Smeaton in his 1760 study of wind and 

water power. Based on John Smeaton, An Experimental Enquiry Concerning the Natural Powers of Water and Wind to Turn Mills, and 

other Machines, depending on a Circular Motion (London: [s.n.], 1760), table VI, page 68.

The collapse of the Firth of Tay high-level bridge in Scotland on December 28, 1879—almost exactly 

three years after the Ashtabula Bridge failure—during a windstorm focused international attention 

on design wind loads. Nonetheless, other than personal experiences, observations, and preferences 

on design wind pressures, no advances in modeling occurred. There was general agreement that, 

given the rare occurrence of large wind pressures, an increase in allowable stresses of between 25 

percent and 33 percent was necessary for wind loads. It probably represented an economizing effort 

to minimize increases in member sizes due to wind. 

In summary, a necessary step in the engineering design process required imagining loading scenarios 

and mathematically modeling the loads. The examples of floor live loads and wind loads show their 

inherently uncertain or random nature. As a consequence, engineers typically defined—and still do 

define—simple static models with magnitudes that were well above average, even when faced with 

the unknown probability of exceeding these loads. Very conservative, highly improbable design 

loads generally led to safer structures, but they could also result in greater, and possibly prohibitive, 

costs. Despite inherent uncertainties and some inconsistencies, simple load models allowed engineers 

to achieve designs with acceptable safety and reliability.
90 Covered Bridges and the Birth of American Engineering

Structural Materials

Alongside developing load scenarios, engineers had to select appropriate structural materials for the 

various bridge components. Wood was the primary material of covered bridge construction. It formed 

the load-bearing structure as well as the distinctive siding and roofing that protected the structure 

from deterioration. Selecting the right wood required careful consideration of the strength, weight, 

resistance to decay, workability, and cost of the woods available. Early-nineteenth-century builders 

tended to use regional timber species. In New England, spruce and eastern white pine grew abundantly 

and were frequently used in covered bridges. Eastern white pine, a light but reasonably strong species, 

also grew in Michigan and Wisconsin and was favored in the Midwest, where white oak and poplar 

were common. Later, as railroads allowed more economical long-distance shipment, southern pine 

was adopted as a strong and cheap alternative throughout the nation. Noted Indiana bridge builder J. 

J. Daniels purchased hundreds of acres of Georgia forest to provide a reliable source of southern pine 

for his business. Douglas fir, the great western building timber, formed the covered bridges of Oregon, 

Washington, and California, but it was not used east of the Great Plains during the nineteenth century.

When a tree is first cut, it has a high moisture content and is said to be green. Green wood shrinks as 

it dries, so cut lumber today is typically prepared for use by seasoning it or drying it in a kiln. Even 

after seasoning, wood remains hygroscopic and continuously absorbs or desorbs water vapor as the 

humidity and temperature of its environment change. Wood, therefore, constantly experiences moistureinduced strains. The mechanical properties of wood strongly depend on its moisture content, and these 

mechanical properties typically degrade as moisture content increases. While some historic wooden 

truss designs, such as Long and Howe trusses, were routinely built using green timbers, nineteenthcentury builders well understood that seasoned lumber produced more stable and long-lasting results. 

Covered bridge builders also understood that the mechanical properties of wood varied depending 

on the presence of knots, checks, shakes, and other flaws. This variability necessitated the use of 

allowable stresses that were small fractions (usually one-fifth to one-tenth) of measured strengths to 

keep the probability of having under-strength members acceptably small. Old-growth timber, from 

which many covered bridges were historically fabricated, was noteworthy for the absence of most flaws.

Early-nineteenth-century builders and engineers possessed a wealth of practical knowledge about wood 

and wood science. Thomas Tredgold’s comprehensive Elementary Principles of Carpentry, published 

in England in 1820 and in the United States in 1837, provides a good window on the extent of that 

knowledge. The book covered wood science, mechanical properties, fabrication technology, common 

structural forms, and structural design guidelines. It discriminated among various wood species, 

distinguished between heartwood and sapwood, prescribed proper felling, sawing, and seasoning 

practices, and discussed decay and decay prevention. Tredgold provided extensive data on the 

mechanical properties of wood such as the modulus of elasticity, crushing strength, and the tensile or 

“cohesive” strength in the axial and radial directions. The woods Tredgold discussed included North 

American white pine, yellow pine, and the wood from a then “unknown species . . . discovered in 

the northwest coast of America by Mr. David Douglas.”20

Tredgold described wood framing techniques for floors, roofs, domes, and bridges and illustrated 

appropriate designs for mortise and tenon joints, scarf joints, and tension splices. He cautioned that “the 
The Engineering Design of Covered Bridges 91

effects of shrinkage and expansion should be considered in the construction of joints,” specifically noting 

that swelling could cause splits and that shrinkage tended to loosen bolts. He also considered the strength 

of columns and beams and suggested that allowable stresses should be one-fourth of measured strengths. 

Tredgold’s data was invaluable to any engineer undertaking the design of covered wooden bridges.21

Stephen H. Long’s 1830 directions to the builders of the Jackson Bridge provide a complementary 

contemporary perspective on wood use in bridges:

The timber best adapted to the construction of a Frame Bridge is White Pine. The 

qualities which entitle it to this distinction are, its lightness, stiffness, and exemption 

from the ravages of worms, insects, &c. Cypress, Yellow Pine, White Cedar, Hemlock, Poplar, and Chestnut, are to be regarded as among the most valuable substitutes 

afforded within the limits of the United States. Yellow, or hard Pine, is probably better 

adapted for the necessary keys and wedges than any other material; but when those are 

not to be had, White Ash, White Oak, Locust, or Chestnut, may be used to advantage. 

The timber employed, especially in the frame-work of the Bridge, should be perfectly 

sound, free from sap, knots, shakes, splits, twists, and all other defects calculated to impair its strength, tenacity, and durability; and should be of the character denominated 

“quartered timber,” or timber cut through, and deprived of, the heart or pith.22

Long’s remarks reveal the clear contemporary understanding that flaws significantly lowered the 

strength of wood. Similarly, Squire Whipple’s 1847 treatise A Work on Bridge Building included 

an extensive discussion of the shear strength of wood.23

Today, it is well understood that wood is a biopolymer consisting mostly of cellulose, which is 

hydrophilic, and lignin, which is relatively hydrophobic. Largely because of its particular cellular 

microstructure, the mechanical properties of wood at a given point depend on the direction of 

applied stresses and strains. Wood strength, stiffness, and many other properties are significantly 

greater in the axial (parallel-to-the-grain) direction than in the radial (perpendicular-to-the-grain) 

and tangential directions. Wood is also a viscous material; if a constant stress is applied to wood, 

the strain increases with time. This phenomenon, called creep, generally causes wood structures 

to deform over time. It also causes changes in member forces in statically indeterminate trusses 

over time.24

By 1830, iron was an essential component of covered bridges as well. The physical and mechanical 

properties of cast iron were well known in the early nineteenth century. In his Practical Essay on 

the Strength of Cast Iron and Other Metals, first published in 1822, Thomas Tredgold provided 

data on the modulus of elasticity, tensile strength, and compressive strength of cast iron, among 

other materials. His principal finding was that the tensile strength of cast iron was much smaller 

than its compressive strength, a fact that led cast iron to be used for compression members but not 

for tension members. Cast iron was also used for beams, but only with great care. “With regard to 

cast iron,” Whipple later wrote, “it is not economical to employ it to sustain tension, and whenever 

it may be exposed to that action, I would not rely on it for more than about 4,000 lbs. to the square 

inch.” Cast iron was most commonly used in wood bridges for the nodes (shoes) on Howe trusses.25
92 Covered Bridges and the Birth of American Engineering

The relatively high carbon content of cast iron lowered its melting temperature and facilitated 

casting, but it also contributed to the material’s low tensile strength. A process for removing carbon 

and other elements from iron was invented by Henry Cort in 1784, which involved oxidizing out 

the impurities in a special furnace called a puddling furnace and then hot working the metal in 

a rolling mill to increase its strength—particularly its tensile strength. This process also lent the 

metal excellent resistance to corrosion. The final product of Cort’s process was wrought iron, and 

wrought-iron components came into common use in covered bridges for tension rods, such as those 

in Howe trusses, and diagonal braces and counterbraces, such as those in wooden Pratt trusses.26 

Wrought iron has a fibrous microstructure as shown in figure 4.14. 

Carbon Silicon Sulfur Phosphorus Manganese

Pig iron 3.5–4.25 1–2 0.30–0.1 0.50–1.00 0.25–1.00

Table 3: Chemical composition of pig and wrought iron (percent by weight). The pig iron from a smelting furnace, while consisting mostly of the element iron, also contained carbon and other elements. Adapted from M. O. Withey and James Aston, with

F. E. Turneaure, ed., Johnson’s Materials of Construction, 5th ed. (New York: John Wiley & Sons, 1919), 545.

 

Figure 4.14 Wrought iron was the final product of changes affected in iron by heating in a puddling furnace and then hot working. 

Table 3 demonstrates that the puddling process removed most of the carbon in the iron and bound the silicon, manganese, and

phosphorus within the slag phase, an important chemical change that, together with the rolling process, gave wrought iron its

unique microstructure and character. The rolling process created slag fibers—whose microstructure is shown in this scanning electron

microscope image of a wrought-iron fracture surface—that are aligned with the rolling direction. The phase marked “A,” which has

a sharp fracture surface, is slag. The presence of slag fibers gave wrought iron both its excellent resistance to corrosion and its ease in

being cut by threading machines. The slag fiber also allows a simple physical test for identifying wrought iron. A specimen suspend ed

for a half hour in a solution of nine parts water, three parts sulfuric acid, and one part hydrochloric acid will etch wrought iron deeply

and unevenly, producing a rough, fibrous, “woody” surface. Courtesy of Professor Gerhard Welsch, Case Western Reserve University.
The Engineering Design of Covered Bridges 93

Wrought iron was supplanted by steel at the end of the nineteenth century, and it is now an archaic 

material, no longer made in industrial quantities. Because of this, wrought-iron components add 

much to the historic fabric of many wooden covered bridges.

Structural design criteria

After deciding on design loads and choosing the proper structural materials, an engineer’s design 

process set structural design criteria. This meant deciding how the bridge was to perform under 

various loading conditions. The general objective of structural design was to create a durable bridge 

that safely carried the design loads without excessive displacements. The principal structural design 

criteria were strength and stability, stiffness, and durability. A structural designer had to assure that 

every member and every connection, as well as the bridge as a whole, had adequate strength and 

remained stable. Any member could fail in a variety of ways, such as from excessive axial forces 

(figure 4.15a), moments (figure 4.15b), or shears (figure 4.15c).

Members not only had to have adequate strength, they also had to be properly connected so that 

loads were transferred to the abutments. Compressive axial forces could cause an initially straight 

member to become unstable; a member could bend or buckle, as shown in figure 4.16.

 

 

 

 

 

Figure 4.15 Three common modes of failure.

Figure 4.16 Member buckling 

from a compressive force.

The compressive stress that caused buckling depended on the member’s end connections and 

the material’s modulus of elasticity. It was also an inverse function of the square of the member’s 

slenderness ratio, defined as:

length of member

k (smallest cross – sectional dimension)

In the above equation, k is a constant, approximately equal to 0.3 for rectangular sections. Lattice 

truss diagonals were often relatively slender and were able to carry only limited compressive forces 

before buckling occurred. It was also possible for the entire compressive chord of a truss to become 

unstable and move horizontally as shown in figure 4.17. This phenomenon is today called lateral 

instability. Both member buckling and lateral instability of compressive chords had to be anticipated 

and prevented.
94 Covered Bridges and the Birth of American Engineering

A bridge could be stable and have adequate strength, but it 

could also be too flexible, such that the imposed gravity loads 

caused excessive vertical displacements or deflections, as shown 

in figure 4.18. Such a bridge is today said to have insufficient 

stiffness and to not meet serviceability requirements. Predicting 

displacements mathematically required significant computations, 

a level of engineering science not achieved until the 1870s. As a 

consequence, historic covered bridge designers depended on the 

empirical knowledge of prior bridges that had proven to have 

adequate stiffness.

Figure 4.17 Lateral instability of a

top chord.

Figure 4.18 Excessive vertical 

displacement or sag in a bridge.

Most importantly, covered bridge designers needed to devise 

systems and details that delayed degradation and the consequent 

loss of strength. The wooden structural framework had to be 

protected from fungal and insect attack and from wetting and 

drying cycles resulting from direct exposure to rain and snow. 

Designers then conceptualized a structural system that met the 

various design criteria.

Conceptual structural design

Covered bridges could be built as through, pony, or deck types, as shown in figure 4.19. The individual 

trusses in the rare wooden pony trusses were often housed, although without a roof over the roadway. 

The type chosen depended largely on the topography and the bridge span. For all types, a principal 

Figure 4.19 Historic examples of through, pony,

and deck trusses include: Top Left: 4.19a) Dover Toll

Bridge, a Howe through truss, carrying a train across 

Great Bay in Dover Point, New Hampshire, prior to being 

covered (stereograph by H. Copeland, 1873);

Top Right: 4.19b) a Howe pony truss on the Portland and 

Ogdensburg Railroad in Crawford Notch through the 

White Mountains in New Hampshire (stereograph by B. 

W. Kilburn, ca. 1870); and Left: 4.19c) an uncovered

Howe deck truss on the Troy and Greenfield Railroad

(stereograph by Horton & Wise, undated). All stereograph

halves courtesy of a private collection.
The Engineering Design of Covered Bridges 95

design parameter was the depth-to-span ratio, 

which strongly affected the stiffness of a bridge. 

This ratio typically ranged from one-fifth to 

one-tenth. Once a depth-to-span ratio was 

chosen, a designer conceptualized systems that 

satisfied the design criteria for all the considered 

loads, effectively visualizing “paths” by which 

the applied loads were transferred to the 

abutments. Often, a designer conceptualized 

a three-dimensional bridge as an assembly of 

two-dimensional, or planar, components, each 

performing separate functions. For example, 

for the dominant gravity dead and live loads, a 

designer visualized the vertical sides of a bridge, 

as shown in figure 4.20, to be the principal 

components that carry the vertical loads to 

the abutments. 

Figure 4.20 The vertical sides of a bridge are the principal 

components for carrying gravity loads, with a variety of truss 

types shown. Before the mechanical properties of trusses 

became well understood and had established reliabilities, 

it was common to add arches as shown in (d), with the arch 

and truss each carrying a fraction of the gravity load.

 

 

 

 

The two vertical sides must generally be 

subdivided or trussed using a variety of 

patterns, such as those shown in figures 4.20a, 

b, and c. (The most widely used trusses are 

described in further detail in chapter 5.) It was 

important to distinguish whether a particular 

trussing pattern was statically determinate or 

indeterminate. Statically indeterminate trusses 

often had “main diagonals” and “counter 

diagonals” in an X pattern. If a truss was 

statically indeterminate, a state of prestress 

could be induced, for example, by driving 

wedges or tightening nuts on threaded iron 

rods. Such a state of pre-stress could increase 

the stiffness of a bridge. In theory, in a 

statically determinate truss, if one member 

failed, the entire truss failed. Conversely, 

the failure of a single member in a statically 

indeterminate truss did not necessarily lead 

to failure of an entire truss. 

Conceptual design also required accounting for wind loads. Common systems devised to resist 

lateral wind forces are shown in figure 4.21. The floor of a typical covered bridge, as previously 

shown in figure 4.10, was conservatively assumed not to be part of the wind load resisting system. 

It was designed only to transfer local floor gravity loads to the lower chords of the vertical trusses. 

The various members were sized to carry the loads within their contributing areas.
96 Covered Bridges and the Birth of American Engineering

Figure 4.21 To transfer horizontal

or lateral wind forces to the abutments, 

designers conceptualized and designed 

horizontal trusses and two-dimensional, or 

plane, frames as shown here. The horizontal 

trusses are at the plane of the floor and at the 

plane defined by the two top chords. For 

pony-type bridges, it was not possible to 

carry wind load and stabilize the top chord 

through a horizontal truss, so outriggers

were installed. Examples of bracing include 

Top Left: 4.21a) horizontal lateral bracing to 

resist wind on the West Union Bridge (1876), 

Parke County, Indiana, HAER IN-105-13, 

James Rosenthal, photographer, 2004; 

Middle: 4.21b) Portal frames to transfer 

loads taken by the top chord on the Flint 

Bridge (1874), Orange County, Vermont, 

HAER VT-29-5, Jet Lowe, photographer, 

2003; 

Bottom L: 4.21c) outriggers to stabilize 

top chords on the Beaverkill Bridge (1865), 

Sullivan County, New York, HAER NY-329-10, 

Jet Lowe, photographer, 2003.
The Engineering Design of Covered Bridges 97

A bridge’s self weight, or dead load, could create a downward vertical displacement, so designers 

generally designed the deck with a small upward displacement, called camber, which ideally was 

equal but opposite to the self-weight displacement (figure 4.22). 

Figure 4.22 The necessary camber for a bridge was generally achieved by making each top chord panel length slightly longer 

than the corresponding lower chord panel length. For example, if the lower chord panel length was 120 inches, the corresponding upper chord panel length was approximately 120.125 inches. The exact length increment was determined mathematically 

by considering the truss to be part of a circular arc. The Humpback Bridge, shown here, displays a 4 percent camber. HAER VA-1, 

sheet 2, Charles King, delineator, 1970.

Durability was, of course, an all-important design criterion involving wood choice and the 

appropriate siding and roofing, carefully detailed to protect the ends of a bridge. Significantly, roofs 

and siding were always viewed as expendable protection for the all-important trusswork and floor 

systems. Their eventual replacement was expected during the service life of a bridge, and failure 

to maintain the coverings has long been a primary reason for the deterioration and loss of covered 

bridges. Occasional modern attempts to preserve the siding and roofing as elements critical to the 

significance of historic bridges fly in the face of the builders’ intent. 

Mathematical modeling and structural analysis

After a design is conceptualized, engineers proceeded with the step that was begun by Navier: 

estimating the forces in all parts of a bridge caused by the design loads in a process known as 

mathematical modeling and structural analysis. Although by 1826 Navier had applied equilibrium to 

determine forces in simple kingpost trusses and had postulated an analogy that enabled estimation 

of forces in truss chords, structural analysis for more complicated truss forms developed slowly over 

the course of the nineteenth century. In fact, the engineering science of computing forces in all 

members of statically determinate trusses only became widely taught and applied in the 1870s, and 

computing forces in statically indeterminate wood trusses remains an uncertain process to this day. 

Equilibrium equations at joints may be solved either algebraically or graphically, using geometry. 

During the nineteenth century, graphical methods were seen as simpler and more efficient and 

offered a visual error check not available through algebra. Some methods of graphical analysis were 

known in France as early as 1725 and were used by engineers in America during the first half of 
98 Covered Bridges and the Birth of American Engineering

the nineteenth century. The earliest American publication to show a graphical method appears to 

have been the first American edition of English engineer Thomas Tredgold’s Elementary Principles 

of Carpentry, published in Philadelphia in 1837. Tredgold demonstrated how to find the resultant 

force on an inclined member using the parallelogram of forces, a theorem whose proof was credited 

to Daniel Bernoulli in 1726.

Tredgold illustrated the method with a simple diagram (figure 4.23a) accompanied by this 

explanation:

Let AC represent the magnitude and direction of a force, acting on the body C, and BC 

the magnitude and direction of another force, also acting on the body C. Then to find 

the resultant, draw bB parallel to AC; and Ab parallel to BC; join bC, which represents 

the resultant required.27

Using the example of a kingpost truss, Tredgold illustrated how the parallelogram of forces could 

be used to analyze a statically determinate truss by calculating the components of axial force in 

each truss member (figure 4.23b). This is the same problem solved analytically by Navier in his 

Résumé des leçons, only now solved geometrically. 

Figure 4.23 Left: 4.23a) Tredgold’s illustration for finding the resultant of two forces graphically. Right: 4.23b) A kingpost 

roof truss used by Tredgold to demonstrate the parallelogram of forces. [Note: C added at top of kingpost.] In this diagram, 

the magnitude of the weight W is known and represented graphically by the length of Cc. Lines ac and bc are drawn parallel to 

members AC and BC, respectively; the lengths of ac and bc then represent the magnitudes of axial force in members AC and BC, 

respectively. Likewise, the horizontal line bf represents the horizontal component of force in BC as well as the thrust at B, and the 

horizontal line ae represents the horizontal component of force in AC as well as the thrust at A. The axial tensile force in member 

AB equilibrated the outward thrusts of AC and BC. From Thomas Tredgold, Elementary Principles of Carpentry (Philadelphia: E. L. 

Carey and A. Hart, 1837), Plate II, Fig. 11, art. 25, and Plate I, Fig. 4, art. 17.

American civil engineers Squire Whipple and Herman Haupt presented methods similar to 

Tredgold’s in publications dating to 1847 and 1851. Graphical methods of analysis gained further 

popularity after the appearance of Karl Culmann’s Die Graphische Statik in 1864, followed by 

works by American engineers Augustus Jay Du Bois, Charles Ezra Greene, and Henry T. Eddy 

in the 1870s.28 In fact, Du Bois pointed out in 1875 that drawing the parallelogram of forces was 

unnecessary. It was much simpler, and just as accurate, to draw the forces (such as ac and bc in 

figure 4.23b) head to tail, with the resultant line drawn from the head of the first force to the tail 

of the last force being the line necessary to close the polygon, and therefore enforce equilibrium. 

Du Bois defined the force polygon as “the polygon formed by the successive laying off of the lines 
The Engineering Design of Covered Bridges 99

parallel and equal to the forces.”29 Squire Whipple was aware of this simplification much earlier, 

demonstrating use of the force polygon in his 1847 publication to graphically find the compressive 

force in the top chord of a truss (figure 4.24). 

Figure 4.24 Whipple used a force polygon to find 

the compressive force in member o-n. From Squire 

Whipple, A Work on Bridge Building: Consisting of Two 

Essays, the One Elementary and General, the Other Giving 

Original Plans and Practical Details for Iron and Wooden 

Bridges (Utica, N.Y.: H. H. Curtiss, Printer, 1847), 12.

The method of joints is the algebraic counterpart of the force polygon, based on satisfying the three 

equations of equilibrium at every joint in a truss. Although Whipple did not name this method 

explicitly, it is clear that he used it in conjunction with the force polygon to determine the forces 

in a truss. 

In addition to promoting the use of force polygons, Du Bois and Greene both presented the idea 

of the equilibrium polygon, a curve used to graphically represent the change in bending moment 

along the length of a beam. Shear and moment diagrams, derivatives of the equilibrium polygon, 

are instrumental in structural analysis today (figure 4.25). 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 4.25 Graphical representa tion of the 

external forces and internal shears and moments 

in a simply-support ed beam under uniform loads. 

The shear diagram (4.25b) demonstrates the 

change in shear V due to load w along the length 

of the beam; and the moment diagram (4.25c) 

demonstrates the change in bending moment

M due to load w along the length of the beam.

Used in concert with Navier’s beam analogy, such graphical representations of moment and shear 

in a beam could be used to calculate stresses in the chords and web members throughout the length 

of a truss. Using Navier’s beam analogy to relate moment and chord force was described earlier 

in this chapter, but the analogy could be extended to calculate forces in the web members of the 
100 Covered Bridges and the Birth of American Engineering

truss as well. Shear forces work to displace the top and 

bottom chords with respect to one another; it is the role 

of the web members to resist that relative displacement by 

developing tensile and compressive stresses. For a uniformly 

loaded beam with simple supports, shear force is highest 

at the ends of the beam and zero at the midpoint (figure 

4.25). For a multiple-kingpost truss of the same length, 

the axial force in each diagonal truss brace is proportional 

to the shear force in the beam at the same location along 

the span, which means that the axial forces in the diagonal 

braces at the truss ends are higher than the axial forces in 

the diagonal braces near midspan of the truss (figure 4.26). 

With this understanding, braces could be sized to meet 

particular allowable stresses, though typically they were all 

the same size, which was dictated by the maximum axial 

force at the truss ends. 

 

 

 

 

 

 

Figure 4.26 In a uniformly loaded beam, the 

shear forces increase linearly from midspan to 

the supports. In a truss, shear forces are carried 

mainly by the diagonals; therefore the forces they 

carry also increase from midspan to the supports.

Stephen Long, who used Navier’s beam analogy to size chord members, did not reveal in his writings 

whether he extended the analogy to size his braces and counterbraces. However, Haupt did so in 

1851 when he demonstrated the use of the beam analogy to calculate axial force in the web members 

of a Town-lattice truss, described in his calculations for the Cumberland Valley Railroad Bridge.30

Mathematical modeling and structural analysis continue to be essential steps in the structural design 

of bridges, although the modeling has become substantially more complex since the development 

of structural analysis computer programs. Nevertheless, the most widely used tool still remains the 

first one formulated by Navier for the statically indeterminate three-member truss: linear elastic 

structural analysis (aka linear elastic finite element analysis), which will be discussed shortly. 

Whether by algebraic or graphical means, bridge engineers used the mathematical modeling tools 

developed by Navier and those who came after him to estimate truss-member forces so that they 

could size the components of their bridges to perform within safe limits. In his Résumé des leçons, 

Navier introduced the idea that the allowable stress of wood in compression should be one-fifth its 

compressive strength. The ratio of actual strength to allowable stress came to be called the factor 

of safety. Tredgold collected and published the results of experimental work performed by Peter 

Barlow and numerous others and recommended a safety factor of four, while Mahan provided 

general values for allowable stresses in tension and compression only, invoking the safety factor of five 

suggested by Navier.31 Numerous other sources between 1837 and 1908 published allowable stress 

values for different species of wood in tension, compression, bending, and shear; these published 

values often disagreed with each other.32 It was not until 1934 that standard values were published 

for engineers’ use in the Guide to the Grading of Structural Timbers and the Determination of 

Working Stresses. This publication not only standardized the allowable stresses used in design; it 

also provided a quantitative method for decreasing allowable stresses to account for knots and other 

natural defects in the wood.33
The Engineering Design of Covered Bridges 101

Foundations

To this point, the discussion of engineering issues has focused on the bridge itself, the superstructure. 

The engineering issues involved with the design of foundations, piers, and abutments were historically 

a vital part of bridge design and also worthy of consideration. For many covered bridges, the 

substructure cost more than the timber span it 

supported. In fact, most covered bridges were 

built through two separate contracts, one for 

the substructure masonry work and another for 

the truss fabrication. Shallows in large streams, 

islands, and rock outcroppings determined a 

bridge’s location and road alignment and could 

lead a builder to construct several shorter spans 

instead of fewer longer ones. Where bedrock lay 

close to the surface, foundation construction 

could be easy and durable. In the absence of 

surface bedrock, a raft of heavy timbers, placed 

as deep below ground level as money and 

equipment would allow, served as a base for 

the foundation stonework. Because floodwaters 

could undercut a raft, this foundation type was 

best used where abutments could be set back 

from the channel and where there was less chance 

of the channel meandering. 

Figure 4.27 Erecting piers in the mid-nineteenth century

for a multi-span bridge across the Merrimack River in Haverhill,

Massachusetts. Half of a stereograph courtesy of a

private collection.

Deeply driven timber piles provided a more reliable foundation base than rafts, especially when 

used beneath piers in a channel. In the nineteenth century, straight tree trunks were the only piles 

available. These were pounded vertically into the ground, below the level desired for the foundation. 

A solid raft was installed atop the piles, and the masonry rose from there. When placed below the 

water table, timber piles and rafts did not decay.

Bridge piers and abutments were typically built of stone before the turn of the twentieth century, 

when concrete was more widely used. The best type of stonework was ashlar masonry, that is, cut 

stone blocks laid in regular courses. Less finished abutments and piers used irregularly sized and 

shaped stones. There was wide variation in stone dimensions, finishes, and mortar joints; for example, 

dry-laid large, flat stones formed the base for many bridges in the Northeast. Stone substructures 

were, in general, highly durable and were frequently reused when covered bridges were replaced. 

Many more survive today than is usually recognized. Often later topped with reinforced-concrete 

caps, they lie beneath more recent spans, continuing to support and carry traffic far beyond the 

lifespan that their builders envisioned.

Mortar provided uniform bearings for all types of masonry, reducing stress cracking and prolonging 

the life of the structure. The earliest builders used lime mortar, a combination of lime, sand, and 

water that gained strength by absorbing atmospheric carbon dioxide as it cured. Lime mortar dissolves 

in water, however, and is not suitable for masonry exposed to water. An important improvement 
102 Covered Bridges and the Birth of American Engineering

in mortar occurred during the construction of the Erie Canal in New York in 1820, when Canvass 

White, an engineer working on the canal, identified a limestone near the canal route that, when 

processed, produced a waterproof hydraulic cement superior to any then in use. White’s cement, 

which he patented, revolutionized the construction of masonry exposed to water. It was used to 

create “hydraulic mortars” that were not only durable in water but actually gained strength with 

exposure to water. An English mason, Joseph Aspdin, recognized that a hydraulic cement could 

be produced by firing and grinding a suitable combination of limestone and clay. He patented his 

process in 1824 and called his product “Portland cement.” By the 1880s, Portland cement had 

replaced natural hydraulic cements in America; to this day it remains the most widely used cement 

in mortar. The two very different types of mortar, their many formulations, and the many ways 

they can be finished—indented, flat, protruding, rounded, or pointed—have led to wide-ranging 

opinions how best to build bridge substructures in stone. 

The choice of truss affected the sizes and details of abutments and piers. A Burr-arch bridge 

required unique, angled bearing surfaces—often called “skewbacks”—in the faces of the abutments 

to receive the ends of the arch rings. Loading in a Town-lattice truss, however, was spread over 

multiple interlaced systems of diagonal boards instead of being concentrated at any single point. 

The abutments for Town lattices had to extend back along the line of the lattice far enough to 

receive the load from each diagonal system, a distance that could be as much as 20 feet, and piers 

had to be wide enough to receive the load from as many of the diagonal systems as possible. This 

explains why major Town-lattice trusses, such as the Cornish-Windsor Bridge, extend a substantial 

distance beyond the face of their abutments and need particularly wide piers. The interdependence 

of superstructure and substructure made selecting the optimal bridge style more complex than 

simply selecting the least expensive truss type.

Figure 4.28 Examples of bolster beams and skewbacks. Left: 4.28a) Bolster beam detail on Hall Bridge, Windham County, Vermont,

installed by Graton Associates in 1982. HAER VT-40-7, Jet Lowe, photographer, 2009. Right: 4.28b) Cast-iron skewback and rod tying

the Burr arch into the limestone abutment of J. J. Daniels’s West Union Bridge (1876), Parke County, Indiana. The arches bear on an

inclined bearing surface called a skewback. HAER IN-105-11, James Rosenthal, photographer, 2004.
The Engineering Design of Covered Bridges 103

Although the adjustable bearings that accommodate expansion and contraction on metal bridges 

were not needed on timber trusses, the chord timbers of covered bridges were placed on bearing 

beams of a durable species like white oak to raise them several inches above the stone abutments. 

This helped insulate the truss timbers from rainstorm splash and condensation. These bearing 

timbers (or bolster beams) were easily replaced if they deteriorated. Many early covered bridges 

also employed inferior arch braces that acted in compression, much like an arch, to decrease the 

tensile forces in the lower chords. 

Joinery 

The strength and durability of a wooden bridge was intimately linked to the quality of the connections 

used to fasten its structural members together. America’s early bridge builders adopted simple wood 

trusses such as the kingpost and queenpost, which had been used for centuries in roofs and bridges 

in Europe. Eighteenth- and early-nineteenth-century roof trusses, such as those illustrated in Peter 

Nicholson’s The Carpenter’s New Guide (1793) and Owen Biddle’s popular Young Carpenter’s 

Assistant (1805), primarily used traditional mortise and tenon joinery, sometimes combined with 

reinforcing wrought-iron straps. As builders sought to span longer distances, carry heavier and faster 

moving live loads, and incorporate greater resistance to the elements, they adopted more innovative 

truss forms and, correspondingly, more innovative joinery.34

Relatively simple truss forms such as the kingpost, queenpost, and multiple kingpost relied on 

diagonal braces to transfer axial forces from the top chords of a bridge to the bottom chords—

following Navier’s beam analogy, the diagonal braces served to resist shear forces. Generally, these 

braces were framed into the posts, either using mortise and tenon joints or by notching the post 

through its entire depth and fitting the end of the brace into the notch. 

Many builders preferred framing the braces into full-depth notches because the mortise and tenon 

joint presented certain shortcomings when used in bridges. It was expensive, requiring skilled 

craftsmen to make precise cuts. Poorly constructed joints were easy to hide, and even the best joints 

were susceptible to rot from water infiltration. As Robert Fulton observed, “Hitherto, in bridges 

not covered from the weather, the immense quantity of mortices and tenons, which, however well 

done, will admit air and wet, and consequently tend to expedite the decay of the weak parts, has 

been a material error in constructing bridges of wood.” Additionally, cutting tenons in the ends of 

compression members also reduced the amount of bearing area available.35

Because braces were oriented to remain in compression under a uniform load, the brace-to-post 

connections had to transfer compressive forces only. Most early carpentry manuals did not provide 

details for brace-to-post connections, but Thomas Tredgold’s Elementary Principles of Carpentry

illustrated several for use in roof trusses. The different connections reproduced in figure 4.29 illustrate 

a detail common to simpler truss forms: a bearing surface on the post perpendicular to the direction 

of the wood fibers in the brace. To provide this surface, the top and bottom of the post had to be 

much wider than the rest of the post, requiring the removal of a significant amount of material 

along the length of the post. Both Tredgold and Dennis Hart Mahan stressed the importance of 

providing such a bearing surface. If it could not be achieved, Tredgold suggested cutting the end 

of the brace so that only a portion of it bore on the post in a direction perpendicular to its fibers. 
104 Covered Bridges and the Birth of American Engineering

Not all builders followed this suggestion. Theodore Burr suggested that braces “may be put into 

the corners where the posts are united to the chord and crown plates without tenon or mortise by 

cutting the angle of the ends of the brace to correspond with the lines of the chords, plates and 

kingposts, allowing the angle to be partly on each as may suit, in equal proportion is best, or by 

square or shoulders with tenon and mortise.”36

 

 

 

 

 

 

 

 

 

Figure 4.29 Tredgold’s 1837 volume 

included examples of brace-to-post 

connections with both Left: 4.29a) 

traditional and Right: 4.29b) rounded 

ends. Tredgold (and Mahan) proposed using rounded surface joints 

so that, as the truss settled, the joint 

simply rotated like a ball in a socket. 

The labor involved in forming them 

likely made them unpopular, and, 

indeed, they are unknown in any 

American bridge. Still, their existence 

illustrates that the short- comings 

of traditional framing were already 

understood, leading bridge builders 

to search for better methods. From 

Tredgold, Elementary Principles of 

Carpentry, Plate XXII.

A significant weakness associated with traditional brace-to-post connections was that, over time, 

truss settlement caused the braces to rotate, leading to an uneven distribution of pressure across the 

connected surfaces. To compensate for this, Tredgold suggested that the joint between the central 

post and the diagonals be left a little open, “so that when the roof settles it may not bear upon the 

acute angle.” (See the top joints in figure 4.29a.)37

As the need for longer trusses emerged, so too did the need for counterbraces to resist the shear 

forces caused by moving live loads. Counterbraces were the diagonal members whose orientation 

was opposite to that of the braces. Under a uniform (dead) load, counterbraces experienced only 

tension forces; since none of the traditional brace-to-post connections could effectively transfer 

tension forces between a wood counterbrace and wood post, the counterbrace was essentially 

ineffective unless called into action by a moving live load (figure 4.30). In addition, timber shrinkage 

and bridge settlement increased the axial compressive forces in the braces and tended to loosen the 

 

 

 

 

 

 

 

 

 

 

 

Figure 4.30 The sense of the forces in the diagonals can change for different positions of a live load. With the live load at point b, 

the force in member gc is compression; when the live load moves to point c, the force in member gc is tension.
The Engineering Design of Covered Bridges 105

counterbraces, making them ineffective. So, while early builders understood that counterbraces were 

necessary to increase the stiffness of a truss (and both Timothy Palmer and Theodore Burr used 

counterbraces in their early long-span bridges), they were rarely employed in simpler truss forms 

because builders lacked effective means for positively connecting them to the posts. 

Builder Lewis Wernwag recognized the shortcomings of mortise and tenon joinery and the problems 

created by timber shrinkage at the turn of the nineteenth century. He went to special lengths to 

prevent dry rot, hoping to forestall these problems in both his famous 1812 design for the 340-foot 

Fairmount Bridge near Philadelphia, known as the Colossus, and his bridge crossing the Delaware 

River between New Hope, Pennsylvania, and Lambertville, New Jersey. By sawing the timbers 

through the heart, Wernwag exposed any defects. He used iron links and screw bolts to provide 

air space between the bridge components. In addition, Wernwag minimized mortise and tenon 

connections, and, as shrinkage appeared in the bridge, the timbers could be screwed closer together.38

Instead of mortise and tenon joints for the diagonal-to-post connections of his bridge crossing the 

Delaware River, Wernwag placed cast-iron shoes on the lower chords at each panel point; the posts 

were positioned in the middle of the blocks while angled bearing surfaces were provided on each 

side for the braces and counterbraces. A bridge company official insisted that the design “guards 

more effectually against decay, perhaps, than any other.” To counteract sagging, Wernwag installed 

wrought-iron rods parallel to each counterbrace that could be tightened as the wood dried.39

Stephen Long revolutionized long-span truss construction with his 1830 patent in which 

counterbraces were prestressed in every panel by driving wooden wedges between the counterbraces 

and chords, thus eliminating the need to provide a positive connection between the counterbraces 

and the posts. As described in chapter 5, if a bridge built to Long’s design sagged due to shrinking 

timbers, the counterbraces would lose some of their compressive force but still retain enough 

compression to remain in place and effective. As the bridge sagged over time, the wedges could be 

further driven in to increase the compressive force in the counterbraces.

Figure 4.31 Long’s prestressing technique allowed counterbraces to be 

effectively incorporated into a truss,

but it required an innovative connection between the diagonal and the 

post, including wooden wedges which 

were driven below the counterbrace to 

induce compression in the member.

HAER OH-122, detail from sheet 6, 

William Dickinson, delineator, 2002.
106 Covered Bridges and the Birth of American Engineering

Despite Long’s innovative method of 

prestressing, his design still required 

laboriously cutting daps (notches) in the 

verticals and the top and bottom chords. 

William Howe’s second 1840 patent, 

however, simplified the prestressing process 

by replacing vertical wood posts with 

threaded wrought-iron rods, which could 

be tightened (post-tensioned) to maintain 

compression in the braces and counterbraces, 

thereby counteracting the effects of long-term increases in strain. Oak angle blocks, through which the 

threaded rods passed, replaced traditional joinery for the brace and counterbrace connections at the 

panel points. Eventually, Howe switched his angle blocks from wood to cast iron, like Wernwag’s in 

the Colossus.40

Figure 4.32 An interior 

panel from Howe’s second 

1840 patent, showing the 

angle blocks at each panel 

point, through which the iron 

rods passed, and to which 

the braces and counterbraces abutted. U.S. Patent 

No. 1,711, August 3, 1840.

Caleb and Thomas Pratt patented another version of the 

prestressed truss in 1844, this time replacing wood braces 

and counterbraces with wrought iron. They achieved 

prestressing by tightening the diagonal members so that 

they carried tension forces, which put the wood vertical 

posts in compression. The braces and counterbraces 

were connected to the panel points through wood 

blocks positioned above the top chord and below the 

bottom chord; they passed through these blocks and 

were secured with nuts. The system was susceptible 

to local crushing of the wood chord members at the 

connection points from the prestressing force in the 

diagonal members.41

Figure 4.33 Typical connection between iron 

rods and lower chord in a Pratt truss. From Herman 

Haupt, The General Theory of Bridge Construction

(New York: D. Appleton and Co., 1851), Plate 6

In a through truss, floor beams transfer floor and live loads to the lower chords at each panel point, 

and these loads are in turn transferred to the posts. Like brace connections, the post-to-lower-chord 

connections used in early American bridge trusses were adapted from traditional roof trusses, in 

which the posts were connected to the lower chords by mortise and tenon joints. Mortise and tenon 

joints alone were incapable of transferring tension forces from the chords to the posts; therefore, 

treenails were driven through the lower chords and the post tenons to connect them (figure 4.35a). 

The capacity of these connections depended on the strength of the treenails, and, as early as 1837, 

Dennis Hart Mahan observed that overstressing of mortise and tenon joints was common due to 

the “practice among workmen to make the hole in the tenon [for the treenail] nearer to the surface 

than that through the mortise, for the purpose of making a close joint.” He thought the technique 

“very pernicious,” as it placed “a great strain on the pin, and on the side of the tenon hole, which 

might cause one or the other to give way, if an additional strain were to take place, arising from 

any motion of the two beams.”42 Early builders commonly supplemented the treenails in mortise 

and tenon joints with iron U-straps in spans over 30 feet.
The Engineering Design of Covered Bridges 107

Figure 4.34 Typical detail of a double-notched post connection. Left: 4.34a) From Henry Jacoby, Structural Details, or Elements of 

Design in Heavy Framing (New York: J. Wiley & Sons, 1909), 135. Right: 4.34b) Detail of Leatherwood Station Bridge (1899), in Parke 

County, Indiana, HAER IN-40-15, Ed Sels, photographer, 1979.

Mortise and tenon joinery fell out of favor in roof trusses about 1840, and Mahan’s Elementary 

Course of Civil Engineering suggests a similar timeline for changes in bridge truss joinery. The first 

edition describes fastening the foot of a kingpost “by a stirrup of iron, or by a tenon and mortise.” 

The third edition, published in 1846, instructs builders instead to make the connection with “a 

bolt, an iron stirrup, or a suitable joint.”43

Mahan’s “suitable joint” was likely the double-notched joint shown in figure 4.34a, commonly 

seen in most surviving covered bridges. Like the mortise and tenon before it, the double-notched 

connection was susceptible to damage from shrinkage. Stephen Buonopane, in his 2010 study of 

Smith-truss connections completed for the HAER program, observed that the shear strength in 

the connection was often compromised by a partial cleavage crack that initiated in the corner of 

the post notch in line with the would-be shear plane. The crack likely began as the post attempted 

to shrink toward its centerline. The shrinkage was opposed, however, by a force stemming from 

the friction between the bottom of the lower chord and the top of the post notch (figure 4.35b).44

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 4.35 Failures in the post-to-lower-chord connection may result from (a) shrinkage in the lower chord in a mortise

and tenon connection and (b) shrinkage in the post in a double-notch connection.
108 Covered Bridges and the Birth of American Engineering

As bridge spans exceeded the length of available timber, the chords had to be fabricated from shorter 

members, often called string pieces, which were connected together through tension splices. Tension 

splices were most often employed in lower chords, but Long described continuous spans which 

required tension splices in the top chords over the piers. Tension splices, no matter how well designed, 

inherently reduced the strength of bridge members. Herman Haupt conservatively suggested in 

1851 that lower chords consist of four parallel beams, with the necessary splices staggered in such 

a way that only a single splice occurred at the center of any one panel. Long suggested three string 

pieces, with the two exterior pieces spliced at the same location along the span, alternating with the 

location of the interior splice. He noted that the exterior pieces, which together made up twice the 

area of the interior piece, should be continuous for as long as possible at the center of the bridge, 

where tension in the lower chord was greatest.45

Bridge builders often used splices such as the fishplate joint and the scarf joint that were common 

in wood shipbuilding. The fishplate joint (figure 4.36) minimized the removal of material from the 

chord member by incorporating a piece of timber bolted to one or both sides of the string pieces 

being spliced. Long specified this type of splice in his 1830 patent, illustrating both wood and 

iron fishplates. When made of wood, the fishplates were cut with notches to fit into corresponding 

notches on the string pieces. Thus, the tension force in one side of the string piece was transferred 

to the other side via the shear and bearing strength of the notches in the fishplate and the string 

piece, as well as the tensile strength of each cross-section. The strength of the joint also depended 

on clamping bolts to prevent rotation in the eccentrically loaded splices; without the clamping 

bolts, the fishplate would flex and fail. Tredgold cautioned bridge builders not to rely too heavily on 

bolt strength, for, as timbers shrank, the clamping force of the bolts diminished as did the friction 

between the connected pieces. If the joint relied too heavily on a small diameter bolt, the bolt 

would crush the timber, causing “the joint to yield.” He suggested that dependence on the bolts be 

lessened “by indenting the parts together . . . or by putting keys in the joint.”46

Figure 4.36 Tabled fishplate joint. From Jacoby, Structural Details, 91.

Where a fishplate joint used exterior pieces to transfer the tension force between string pieces, a scarf 

joint relied only on notches cut into the ends of the two chord members being joined. Tredgold noted 

that because making a scarf required removing at least half the cross-sectional area of each timber 

being joined, these joints were more vulnerable to tension rupture than fishplate joints. Therefore, 
The Engineering Design of Covered Bridges 109

he advised that scarf joints should only be used “wherever neatness is preferable to strength.” As 

in fishplate joints, clamping bolts were required in scarf joints to prevent excessive flexural stresses 

from developing in the string pieces.47

 

Figure 4.37 (a) Half-lapped scarf joint, (b) with keys. From Jacoby, Structural Details, 125.

 

Figure 4.38 (a) Straight tabled scarf joint, (b) with key. From Jacoby, Structural Details, 126

 

Figure 4.39 (a) Oblique tabled scarf joint (b) with key. From Jacoby, Structural Details, 127.

Ithiel Town’s lattice trusses were constructed entirely of wood, yet they avoided both mortise 

and tenon joints and tension splices, relying instead on lapped joints connected by treenails to 

transfer loads between members. Town instructed builders of his truss design to use round, 1-1/2 

inch diameter seasoned treenails cut from white oak, with three to four treenails per joint. Town 

claimed that the redundancy of having a considerable number of connections transferring shear 

forces from the chords through the lattice into the abutments was “a very important advantage 

over any other mode.”48

Town’s lower chords were built up from two beams, approximately 3 to 3-1/2 inches thick by 10 to 

11 inches wide, with joints staggered along their length. Treenail connections between the chords 

and the lattice members were so regularly spaced that creating tension joints in the lower chords 

was unnecessary. Historic preservation engineer David Fischetti has suggested that treenails both 

united the chords and lattice together and allowed for “load sharing within the individual chord 

sticks to provide continuity through joint locations.”49

Herman Haupt acknowledged that the force in the diagonal ties and braces in a Town-lattice 

truss was difficult to estimate correctly. The ability of Town’s treenail connections to transfer loads 

depended on the treenails’ strength in bearing perpendicular to grain, in horizontal shear, and in 

bending, as well as the strength of the lattice members in bearing on end grain. Civil engineer 

Lewis M. Prevost noted in the 1840s that the lattice members were known to split at their ends as 

a result of the treenails bearing on end grain. Squire Whipple thought the treenails themselves, not 

the lattice members, limited the strength of the connections, since their lateral strength was less 

than the strength of the end grain of the lattice members through which they passed.50
110 Covered Bridges and the Birth of American Engineering

Figure 4.40 Treenail connections on the Town lattice of Nichols Powers’s Brown Bridge (1880), Rutland County, Vermont. Four 

treenails per joint were used on the primary and secondary upper chords, while two treenails were adequate on the typical lattice 

connections. HAER VT-28, sheet 6, Naomi Hernandez, delineator, 2002.

After 1830, the construction of heavy timber roof trusses was outpaced by light wood roof trusses, 

as stick framing became a more economical type of building construction. The economy came, in 

part, from the reduced skill needed for light wood frame construction. Light wood roof trusses did 

not require—nor could they accommodate—traditional wooden joinery; as a consequence, metal 

dowel-type connectors and, later, metal plates, replaced such detailing. Covered wooden bridges 

continued to be built using traditional methods and traditional joinery, particularly in rural areas, 

where heavy timbers and skilled craftsmen were available, but at a reduced rate. Even when new 

covered bridges are constructed, it is more common to see modern engineered solutions to either 

reduce the number of connections needed (such as glued laminated lower chords to eliminate the 

need for traditional tension splices) or to simplify the bridge’s construction and maintenance. 

Present-Day Engineering Design and Covered Bridges

By the 1830s, American bridge builders, benefiting from the work of Navier, had begun incorporating 

the science of structural engineering into their work. Some, like Stephen Long, had the advantage of 

formal education, but many learned their trade while working on that great engine of innovation, the 

American railroad. Understanding the evolution of their engineering knowledge is vital to appreciating 

and preserving innumerable historic covered bridges. This greater historical awareness has also informed 

a new era of covered bridge building, so that covered bridge construction is no longer a lost art.

Over time, standards and codes have been developed that prescribe loads, design procedures for 

wood, safe bridge geometries, and other safety features. These regulatory standards constrain the 

design of new covered bridges far beyond those with which nineteenth-century bridge designers 
The Engineering Design of Covered Bridges 111

and builders worked. Moreover, the design process now includes more stakeholders with different 

views of the cultural role of covered bridges, appropriate materials, structural forms, and appearance. 

Structural engineers need to be responsive to this variety of viewpoints while designing bridges that 

meet all safety requirements. Creating a responsive engineering design for a new covered bridge 

requires a deep understanding of historic designs. 

The Federal Highway Administration’s Covered Bridge Manual and David Fischetti have presented 

case studies of new covered bridge designs.51 Many more new covered bridge designs will be found 

in the portfolios of engineering firms that specialize in heavy timber framing and covered bridges. 

In addition to designing new covered bridges, structural engineers are commonly called upon to 

assign live-load capacities and to design rehabilitations, or interventions, for existing bridges. These 

tasks are arguably more challenging than designing new bridges because they require an appreciation 

for and an understanding of the historic engineering designs and the processes that resulted in the 

construction of these bridges. The structural assessment of a standing structure by engineers includes 

the condition of a bridge’s materials, connections, vertical- and lateral-load carrying systems, floors, 

bearings, and foundations. The most widely used tools are inspection and analytical modeling, but 

the engineer’s toolkit also features non-destructive testing and ad hoc load testing. Considerable 

uncertainty often remains following an assessment, and load ratings must necessarily be conservative, 

since the methods used have not been calibrated by actual strength tests in the field. 

Whether designing a new bridge, load rating an existing bridge, or designing a rehabilitation, 

the main tool used by structural engineers is linear elastic finite element analysis (LEFEA) of 

mathematical models of a bridge. If material properties are conservatively estimated and the 

strengths of the connections are assured, then a design procedure based on LEFEA leads to a bridge 

strength that is greater than the loads the bridge was designed to support. Because LEFEA does 

not estimate the actual strength of a bridge or its subsystems, the reliability of a design cannot 

be estimated. In general, engineers to this day are not able to precisely predict the strength of 

statically indeterminate wood trusses. Linear elastic structural analysis involves working with 

significant uncertainties, especially when engineers use it to assess historic covered bridges for 

rehabilitation. To start, the material elastic properties of a bridge’s structural components are 

usually uncertain, as are the initial member stresses induced during fabrication and erection. The 

time-dependent stress/strain behavior of wood can cause a redistribution of forces in statically 

indeterminate trusses that is difficult to account for, and even the inevitable minor foundation 

settlements can influence forces in wood bridges. Finally, the modeling of connections is difficult 

and produces highly uncertain results. These issues combine with uncertainty in the loads to make 

the results of linear elastic analyses highly approximate. Perhaps the most significant limitation 

of LEFEA is that it provides only a lower-bound estimate of the strength of a bridge, and even 

this estimate is generally uncertain because connection strength rather than member strength 

can determine the capacity of a bridge.

The historic period of covered bridge construction in America was a time of innovation and creativity. 

Capitalizing on the vast woodlands native to the country, bridge builders, intent on providing strong, 

durable bridges as economically as possible, devised a wide range of structural systems. Various 
112 Covered Bridges and the Birth of American Engineering

designs adjusted to and reflected the needs and constraints of regional and local conditions. It was 

also an era when American engineers began the development of scientific methods for bridge design, 

and many covered bridges played key roles in the refinement of that process.

The increasing sophistication of bridge design coincided with the growth of American railroads, and 

covered bridges provided an economical and efficient design choice as these lines expanded across 

the nation. Because of this early adoption, covered bridges—which are now exclusively linked with 

highways—were important elements in the innovations fostered by civil engineers working for the 

railroads. Since so few railroad covered bridges remain today, it is easy to overlook their critical 

place in the gradual professionalization of American engineering.

Beyond this purely historical perspective, an appreciation of the engineering heritage and thought 

processes that resulted in the completion of these bridges is important as a guide for those planning 

historic preservation projects. Judgments on the proper technique for a restoration or rehabilitation 

of a historic bridge must start with an understanding of the original decisions made in the creation 

of that structure. Every historic project administrator must gain a respect for the men who designed 

and built America’s covered bridges. And that respect begins with a thorough understanding of 

the thought processes that went into the creation of a covered bridge, thought processes we label 

historic engineering concepts.
The Engineering Design of Covered Bridges 113

Endnotes

1 Eda Kranakis, Constructing a Bridge: An Exploration of Engineering Culture, Design, and Research in 

Nineteenth Century France and America (Cambridge, Mass.: MIT Press, 1997).

2 Thomas Young, A Course of Lectures on Natural Philosophy and the Mechanical Arts, 2 vols. (London: J. 

Johnson, 1807).

3 See for example Lorenzo Mascheroni, “Nuove ricerche sull’ equilibrio delle volte,” Biblioteca Scelta di 

Opere Italiane Antiche e Moderne 236 (1829).

4 D. A. Gasparini and Caterina Provost, “Early Nineteenth Century Developments in Truss Design in 

Britain, France and the United States,” Construction History 5 (1989): 22.

5 Stephen H. Long, “Railways and Canals,” Port Folio 276 and 277 (May and April 1825), 353.

 6 Stephen H. Long, “Description of a Patent for Certain Improvements in the Construction 

of Wooden or Frame Bridges,” Journal of the Franklin Institute 5, no. 4 (April 1830): 231–35. 

This article was republished in Stephen H. Long, Description of the Jackson Bridge together with 

Directions to Builders of Wooden or Frame Bridges (Baltimore: Sands & Neilson, 1830).

 7 Long, Description of the Jackson Bridge; Stephen H. Long, Description of Col. Long’s Bridges, 

Together With a Series of Directions to Bridge Builders (Concord, N.H.: John F. Brown Printers, 

1836).

 8 George W. Cullum, Biographical Register of the Officers and Graduates of the U.S. Military Academy 

at West Point . . . , vol. 1 (New York: D. Van Nostrand, 1868), 256–57.

 9 Dennis Hart Mahan, An Elementary Course of Civil Engineering for the Use of the Cadets of the 

United States Military Academy, 1st ed. (New York: Wiley and Putnam, 1837), quote from p. vii.

 10 C. L. Navier, Rapport à Monsieur Becquey . . . et mémoire sur les ponts suspendus (Paris: 

L’Imprimerie Royale, 1823); Stephen Buonopane and David Billington, “Theory and History of 

Suspension Bridge Design from 1823 to 1940,” Journal of Structural Engineering 119, no. 3 (March 

1993): 954–77.

 11 Tom F. Peters, Transitions in Engineering: Guillaume Henri Dufour and the Early 19th Century 

Cable Suspension Bridges (Boston: Birkhäuser Verlag, 1987), 111.

12 Peters, Transitions in Engineering, 111.

13 Gasparini and Provost, “Early Nineteenth Century Developments,” 28–30; S. H. Long, Rail Road 

Manual, or a Brief Exposition of Principles and Deductions Applicable in Tracing the Route of a Rail Road

(Baltimore: Wm. Wooddy, Printer, 1828).

14 Squire Whipple, A Work on Bridge Building Consisting of Two Essays, the One Elementary and General, 

the Other Giving Original Plans and Details for Iron and Wooden Bridges (Utica, N.Y.: H. H. Curtiss, 

Printer, 1847), 83; Herman Haupt, The General Theory of Bridge Construction (New York: D. Appleton 

and Co., 1851), 99.

15 J. A. L. Waddell, General Specifications for Highway Bridges of Iron and Steel, 2d ed. (Kansas City, 

Mo.: Selden G. Spencer, 1889), 25.

16 John C. Trautwine, The Civil Engineer’s Pocket-Book (Philadelphia: Claxton, Remsen & Haffelfinger, 

1872), 519; idem, The Civil Engineer’s Pocket-Book (New York: Wiley, 1904), 713.

17 G. Bouscaren, Report on the Progress of Work and Cost of Construction of the Cincinnati Southern 

Railway (Cincinnati: Wrightson & Co., 1878).
114 Covered Bridges and the Birth of American Engineering

18 Theodore Cooper, “General Specifications for Iron Bridges,” Engineering News (May 31, 1879), 

174–75.

19 John Smeaton, An Experimental Enquiry Concerning the Natural Powers of Water and Wind to 

Turn Mills, and other Machines, depending on a Circular Motion (London: [s.n.], 1760), 67–68; 

Julius Weisbach, Principles of the Mechanics of Machinery and Engineering, edited by Walter R. 

Johnson, 2 vols. (Philadelphia: Lea and Blanchard, 1848–49).

20 Thomas Tredgold, Elementary Principles of Carpentry (Philadelphia: E. L. Carey and A. Hart, 

1837), 245.

21 Tredgold, Elementary Principles of Carpentry, 172.

22 Long, Description of the Jackson Bridge, 9.

23 Whipple, Work on Bridge Building, 95–98.

24 Lorna J. Gibson and Michael F. Ashby, Cellular Solids: Structures and Properties (Cambridge: 

Cambridge University Press, 1999).

25 Thomas Tredgold, Practical Essay on the Strength of Cast Iron and Other Metals (London, 1822); 

Whipple, Work on Bridge Building, 59.

26 R. A. Mott, Henry Cort, The Great Finer: Creator of Puddled Iron (London: Metals Society, 1983).

27 Tredgold, Elementary Principles of Carpentry, 13.

28 Whipple, Work on Bridge Building; Haupt, General Theory of Bridge Construction; Karl Culmann, 

Die Graphische Statik (Zurich: Verlag Von Meyer & Zeller, 1864); Augustus Jay Du Bois, The 

Elements of Graphical Statics and Their Application to Framed Structures (New York: John Wiley 

and Sons, 1875); Charles E. Greene, Graphics for Engineers, Architects, and Builders: A Manual 

for Designers, and a Text-Book for Scientific Schools, Trusses and Arches Analyzed and Discussed by 

Graphical Methods (New York: John Wiley and Sons, 1879); Henry T. Eddy, New Construction in 

Graphical Statics (New York: D. Van Nostrand, 1877); Stephen P. Timoshenko, History of Strength 

of Materials (New York: McGraw-Hill Book Company, 1953). Dr. Frank Rausche translated the 

works of Culmann for Dario Gasparini.

29 Augustus Jay Du Bois, The New Method of Graphical Statics (New York: D. Van Nostrand 1875), 

11; Whipple, Work on Bridge Building, 12.

30 Haupt, General Theory of Bridge Construction, 237–41.

31 Tredgold, Elementary Principles of Carpentry, 40; Mahan, Elementary Course of Civil Engineering, 39.

32 See, for example, Whipple, Work on Bridge Building; Haupt, General Theory of Bridge 

Construction; Augustus Jay Du Bois, The Strains in Framed Structures (New York: John Wiley and 

Sons, 1883); Milo S. Ketchum, The Design of Highway Bridges and the Calculation of Stresses in 

Bridge Trusses (New York: Engineering News Publishing Co., 1908).

33 T. R. C. Wilson, Guide to the Grading of Structural Timbers and the Determination of Working 

Stresses, Miscellaneous Publication No. 185 (Washington, D. C.: U.S. Department of Agriculture, 

1934).

34 Llewellyn Edwards, A Record of History and Evolution of Early American Bridges (Orono, Maine: 

University Press, 1959); Jan Lewandowski, et al., Historic American Roof Trusses (Becket, Mass.: 

Endnotes
The Engineering Design of Covered Bridges 115

Timber Framers Guild, 2006); Peter Nicholson, The Carpenter’s New Guide (London: J. Taylor, 

1808), plate 42.

35 Robert Fulton quoted in Ithiel Town, “A Description of Ithiel Town’s Improvement in the 

Construction of Wood and Iron Bridges: Intended as a General System of Bridge-Building . . . ,” 

American Journal of Sciences and Arts 3, no. 1 (New Haven, Conn.: S. Converse, 1821): 165.

36 Tredgold, Elementary Principles of Carpentry, 163; Mahan, Elementary Course; Burr quote from 

Edwards, Record of History and Evolution of Early American Bridges, 51.

37 Tredgold, Elementary Principles of Carpentry, 162.

38 Lee H. Nelson, The Colossus of 1812: An American Engineering Superlative (New York: ASCE 

Press, 1999), 32.

39 Nelson, Colossus of 1812, 38.

40 Robert Fletcher and J. P. Snow, “A History of the Development of Wooden Bridges,” American 

Society of Civil Engineering Proceedings 53 (1932): 1455–98.

41 Dario Gasparini and David Simmons, “American Truss Bridge Connections in the Nineteenth 

Century. I: 1829–1850,” Journal of Performance of Constructed Facilities 11, no. 3 (August 1997): 

119–29.

42 Quote from Mahan, Elementary Course, 107.

43 Mahan, Elementary Course, 1st ed. (1837), 164; Mahan, Elementary Course, 3rd ed. (1846), 177.

44 Stephen Buonopane, “Structural Study of Smith Trusses,” HAER No. PA-645, 2010.

45 Long, Description of Col. Long’s Bridges, 30-31; Haupt, General Theory of Bridge Construction, 

116.

46 Tredgold, Elementary Principles of Carpentry, 157.

47 Tredgold, Elementary Principles of Carpentry, 157.

48 Ithiel Town, A Description of Ithiel Town’s Improvement in the Construction of Wood and Iron 

Bridges (New Haven: S. Converse, 1821), 163.

49 David Fischetti, Structural Investigation of Historic Buildings: A Case Study Guide to Preservation 

Technology for Buildings, Bridges, Towers, and Mills (Hoboken, N.J.: John Wiley and Sons, 2009),

217.

50 Haupt, General Theory of Bridge Construction; Lewis M. Prevost, “Description of Howe’s Patent 

Truss Bridge,” Journal of the Franklin Institute 3, no. 5 (May 1842): 289–92; Whipple, Work on 

Bridge Building, 97.

51 P. C. Pierce, R. L. Brungraber, A. Lichtenstein, and A. Sabol, Covered Bridge Manual, publication 

no. FHWA-HRT-04-098 (U. S. Department of Transportation, Federal Highway Administration, 

Turner-Fairbank Highway Research Center, April 2005); Fischetti, Structural Investigation of 

Historic Buildings.

Endnotes

117

Chapter 5

The Development of

the American Truss

by Dario Gasparini, Rachel H. Sangree, and Matthew Reckard; 

edited by David A. Simmons

The Development of the American Truss

The sixteenth-century Italian architect Andrea Palladio is generally credited with developing the 

structural form known as the truss, which is a simple framed structure composed of straight members 

connected together to act as a single rigid body. The simplest possible truss is a triangle, and any 

truss is essentially an assemblage of connected triangles. A discussion of the most important truss 

systems used by American wooden-bridge builders follows. 

Early Truss Forms

Truss bridges in America developed gradually 

from simpler structural forms. The simple beam 

bridge set on piles was the most common waterway 

crossing used in seventeenth- and eighteenthcentury America. Examples include the Charles 

River bridge built in 1660, a bridge erected in 1792 

over the Merrimack River, and another that crossed 

the Mohawk River in 1795. Early bridge historians 

suggested that these structures were modeled after 

the famous ancient bridge built over the Rhine in 55 

BC on Julius Caesar’s orders, but it is more likely that 

carpenters simply applied their general knowledge 

of construction to create these practical forms. The 

drawbacks with this type of bridge were that ice flows 

and high water could “quickly carry it seaward in 

little pieces.” Nevertheless, simple beam bridges are 

still in use today, though they are normally reserved 

for spanning small waterways in rural areas.1

Figure 5.1 Roman Bridge over the Rhine. From Thomas Pope, 

A Treatise on Bridge Architecture (New York: A. Niven, 1811), 40. 

Courtesy of George Peabody Library, The Sheridan Libraries, 

Johns Hopkins University.

To extend the length of a simple beam bridge, inclined struts were sometimes installed between the 

abutment faces and the bottom of the beam, effectively shortening the span length of the simple 

beam. Early-nineteenth-century civil engineer Dennis Hart Mahan described several methods for 

executing this form while minimizing stresses at the point of contact between the strut and the 
118 Covered Bridges and the Birth of American Engineering

beam, including proposing the addition of a “straining beam” between the ends of the struts (figure 

5.2a). This form also had an ancient precedent, having been used by Palladio for his 1569 bridge 

at Bassano (figure 5.2b). Col. Enoch Hale reportedly built the first strutted beam bridge in the 

United States in 1785 over the Connecticut River at Bellows Falls, Vermont.2

Figure 5.2 Left: 5.2a) Illustration of a longitudinal beam c strengthened with the use of corbels e and a straining beam f from

Dennis Hart Mahan, An Elementary Course of Civil Engineering (New York: Wiley and Halstead, 1857), 176; Right: 5.2b) Palladio’s Bridge

at Bassano, from Andrea Palladio, The Four Books of Architecture (reprint, New York: Dover Publications, Inc., 1965), third book, plate VI.

Despite the innovation of Hale’s bridge, placing struts below the deck of a bridge was often impractical 

because it left them vulnerable to damage from waterway debris and decay from exposure. Furthermore, 

struts provided limited opportunities for increasing the length of a crossing. The next logical step was to 

shift the struts and the straining beam to a position above the deck. Kingpost and queenpost trusses—

the “royal family” trusses as they were called by historian Richard Sanders Allen—had long been used 

in roof construction before being adopted by bridge builders. Both forms employed a “suspension piece” 

to support the deck; the kingpost used a single, central suspension piece for spans between 20 and 30 

feet (figure 5.3), and the queenpost extended that span length by using dual suspension pieces with a 

straining beam between (figure 5.4).3

Under an evenly distributed load (e.g. when 

the self-weight or “dead” load was more or less 

evenly distributed to each panel point), the kingand queenpost bridges transferred loads to the 

abutments through tension in the posts and lower 

chord, compression in the braces, and, in the 

case of the queenpost truss, the straining beam 

(figures 5.3a and 5.4a). Live loads caused a similar 

distribution of axial forces in the kingpost (figure 

5.3b), as there was only one lower panel point 

between supports—at midspan—for live load to be 

transferred from the road surface to the truss. In the 

queenpost, on the other hand, the existence of two 

panel points meant that live load was transferred to 

the truss asymmetrically, causing shear deformation 

in the traditionally open center panel; for this 

reason, Mahan suggested that bracing be provided 

in the center panel for queenposts of longer spans.4

Assuming that the center panel braces could resist 

Figure 5.3 Axial forces that develop in a kingpost truss 

resulting from Left: 5.3a) dead load and Right: 5.3b) dead 

load and live load. Thick red lines indicate compression, thin 

blue lines indicate tension.

Figure 5.4 Axial forces that develop in a queenpost truss 

from Left: 5.4a) dead loads and Right: 5.4b) an asymmetric 

live load. The braces in 5.4b) were suggested by Mahan in 1857 

to resist shear caused by the asymmetric live load. Thick red 

lines indicate compression; thin blue lines indicate tension; 

and dashes indicate zero force, assuming that the brace-topost connection is unable to transmit tension forces.
The Development of the American Truss 119

only compressive forces (reliable tension connections were difficult to construct), an asymmetric live load 

would produce compression in one brace and no force in the other (figure 5.4b). 

The simple kingpost form could be expanded into a multiple 

kingpost to span longer distances. The Humpback Bridge 

in Alleghany County, Virginia, was built in 1857 with a 

span of 85 feet 10 inches (see figure 4.22 in chapter 4). This 

remarkable length was achieved both by a significant amount 

of camber as well as below-deck struts supporting the outer 

panels of the lower chord. In general, the greater number 

of brace‐to‐post connections in multiple-kingpost trusses, 

which were normally constructed using traditional mortise 

and tenon joinery, led to greater flexibility in these bridges 

as the members shrank and the joints loosened over time.

In addition, an absence of counterbraces in a multiplekingpost truss did not provide the stiffness necessary to 

resist the shear caused by moving live loads (figure 5.5). 

Figure 5.5b, like figure 5.4b, assumes that no tension force 

may be developed in the braces. Success in long-span 

bridge construction required innovative truss forms that 

utilized arches and counterbraces to reduce the effects 

of shrinkage and creep and to stiffen the truss against 

moving live loads. 

Figure 5.5 Axial forces that develop in a king 

post truss resulting from Top: 5.5a) dead load 

and Above: 5.5b) dead load and live load. Thick 

red lines indicate compression, thin blue lines 

indicate tension, and black dashes indicate 

zero force.

Burr-Arch Truss

Figure 5.6 Theodore Burr, drawing from U. S. Patent No. 2,769X, April 3, 1817.

Several early bridge builders, both European and American, recognized the strength of a bridge 

form that combined an arch with a truss. The Grubenmann’s Wettingen Bridge of 1764–66, 

Timothy Palmer’s Permanent Bridge of 1805, and Lewis Wernwag’s “Colossus” of 1812 all employed 

some combination of arch and truss to provide the necessary strength and stiffness for a wide 

river crossing. Theodore Burr was the first to patent such a form. Burr took out two patents in his 

lifetime, one in 1806 (no. 662X) and one in 1817 (no. 2,769X); both patents were destroyed in the 

patent office fire of 1836, but the 1817 patent drawing (figure 5.6) was recovered. Prior to settling 

on his 1817 patent, Burr spent several years experimenting with various truss forms. Among them 
120 Covered Bridges and the Birth of American Engineering

was the 175-foot Waterford Bridge, built in 1804 across the Hudson River between Waterford and 

Lansingburgh, New York (figure 5.7). The bridge consisted of a parallel-chord truss with braces and 

counterbraces in each panel connected to a superimposed arch springing between the abutments. 

Around the same time that Burr was working on the Waterford Bridge, he erected a bridge over 

the Delaware River near Trenton, New Jersey, that suspended the deck below tied wooden arches 

using iron chains (figure 5.8). The Trenton Bridge was replaced in 1876 but was much respected 

and discussed by contemporary engineers. Burr’s Mohawk River Bridge at Schenectady, New York, 

built in 1808, was an experiment with a wooden suspension form (figure 5.9). While the bridge 

stood until 1873, significant deflections became a problem after only twenty years, and additional 

piers were needed to support the bridge at the middle of each span.5

Figure 5.7 Burr’s bridge across the Hudson River between Waterford and Lansingburg, New York. From Theodore Cooper, “American 

Railroad Bridges,” Transactions of the American Society of Civil Engineers 21 (July–December 1889): plate VI.

Figure 5.8 Burr’s bridge across the Delaware River south of Trenton, New Jersey. Left: 5.8a) From Cooper, “American Railroad Bridges,”

plate VII; Right: 5.8b) half of an undated stereograph of the multi-span Burr arches of the Trenton Bridge, courtesy of a private collection.
The Development of the American Truss 121

Figure 5.9 Burr’s bridge across the Mohawk River at 

Schenectady, New York. Top: 5.9a) From Cooper, “American 

Railroad Bridges,” plate VII; Left: 5.9b) stereograph half by Henry 

Tripp, photographer, ca. 1871, courtesy of a private collection.

The success and simplicity of the Waterford Bridge likely led Burr to adopt it as his 

signature form. In 1814, Burr began a two-year period of prolific bridge construction 

across the Susquehanna River. Bridges constructed included Northumberland-toSunbury (1814), McCall’s Ferry (1815), Columbia-Wrightsville (1815), Berwick (1815), 

and Harrisburg (1816). Unfortunately, only the Northumberland and Harrisburg 

bridges withstood the river’s power; McCall’s Ferry Bridge was taken down by ice just 

three years after it was built. Columbia-Wrightsville Bridge was destroyed in an 1832 

flood, and the Berwick Bridge met a similar fate in the winter of 1836. The collapse of 

McCall’s Ferry Bridge must have been devastating to Burr, for its long span exceeded by 

20 feet Lewis Wernwag’s legendary “Colossus,” constructed across the Schuylkill River 

in 1812—and so named because of its extraordinary span length (340 feet!) for its time.6

No practical means of analysis for this highly indeterminate truss form existed 

during Burr’s time. Modern engineering studies suggest that most Burr-arch trusses 

were designed so that each system—arch and truss—could support the entire dead 
122 Covered Bridges and the Birth of American Engineering

load. Nineteenth-century engineer Herman Haupt examined the load-sharing between a Howe 

railroad truss and its superimposed arch and concluded that “it will generally happen that after a 

bridge has been a long time in operation, the two systems bear very unequal portions.” If the truss 

itself was not constructed to allow for adjustment, he went on, “the arch almost always sustains 

the whole weight of the bridge, and its load.” 7

 Modern analysis confirmed Haupt’s claim that, 

over time, creep, shrinkage, and the loosening of the truss joints would result in an increased 

reliance on the arch to support all of the dead load. However, the truss had a much larger role to 

play in supporting the dead load during and just after construction, and the initial distribution 

of dead load between truss and arch was primarily determined by the method of construction 

selected by the builder.8

 Burr’s 1817 patent description, as recorded by Llewellyn Edwards, may 

shed some light on the method of construction he followed.

Both the chord and crown plates may be of two pieces, each embracing the kingpost between 

them, and are put together by lock-work or they may be single and put together by tenons 

and mortises or partly on the one plan and partly on the other, as may suit the builder. When 

put together put in the kingpost or diagonal braces. They may be put into the corners where 

the posts are united to the chord and crown plates without tenon or mortise by cutting the 

angle of the ends of the brace to correspond with the lines of the chords, plates and kingposts, 

allowing the angle to be partly on each as may suit, in equal proportion is best, or by square 

or shoulders with tenon and mortise. After this is done and the bridge is so far raised, attach 

cross beams on the chords and on the crown plates as horizontal braces, either by iron bolts, 

spikes or by mortises and tenons so as to keep the bridge from any side sway or lateral motion. 

There may be two, three or more ribs, segments or sections to make the bridge of any width 

required for carriage ways and foot walks . . . the arches are the last principal timbers that are 

to be raised; they may be notched a little where they cross the chords and where they cross 

the kingposts and braces, if thought best, but seldom necessary on the posts or braces. The 

arches may take their rise from below the chord, or at the chord line, as may be required to 

give the direct curve and to rise to the top of the crown plate or towards it, and even above 

it in very long spans if desired and may be double or single, if double one arch on each side 

of the kingpost and braces; they are put on so as to leave the kingpost between the arches 

when double, if they are left single to be put on that side of the kingpost that suits best.9

Burr’s patent description left out specific details on removing the scaffolding supporting the bridge during 

construction. American civil engineer Herman Haupt understood the implications of timing this step.

If, for example, a truss be constructed, and the false works removed before the introduction 

of the arches, if the latter be bolted to the posts, the weight of the whole structure is 

sustained by the truss itself, and the arches will not bear a single pound, unless they are 

called into action by an increased degree of settling in the truss. . . .

Again; if we suppose the arches to be connected with the truss before the removal of the 

false works, and the joints be equally perfect in both systems, there is a prospect of a more 

nearly uniform distribution of the load; but even in this case, we cannot tell what portion 

is sustained by each system, because this will depend upon their relative rigidity.10
The Development of the American Truss 123

Both methods described by Haupt were used in the nineteenth-century construction of Burr-arch 

trusses in Indiana. J. J. Daniels, who built the Jackson Covered Bridge in Parke County, adopted 

the first method described by Haupt; the Kennedy family, who built Kennedy Bridge in Rushville 

and Forsythe Bridge in the vicinity of Moscow, Rush County, adopted the second method.11

A letter Burr wrote to Reuben Fields in 1815 about the construction of McCall’s Ferry Bridge 

suggested that Daniels’ method of allowing the truss to settle under dead load before completing 

the arch followed Burr’s methods more closely than did Kennedy’s. In the letter, Burr indicated 

that after constructing the truss, he erected the ends of the arch where they sprang from the 

abutment faces. While the constructed portions of the arch were connected to the truss, the arch 

itself was left open in the center of the span. Burr then “cut off the scaffold posts at the bottom, 

some more some less, from one to twelve inches” so that the truss would settle to a predetermined 

camber and, as it did, it would “bring the whole arch to its perfect height and curve.” In the final 

step, which completed the bridge, Burr “united the centre” of the arch, thus enabling the arch 

to fully share any increase in dead load with the truss.12 Following Burr’s method, the initial 

distribution of dead load between the arch and truss was likely more balanced than Daniels’s, 

but less so than Kennedy’s, demonstrating yet one more possibility for the initial distribution of 

dead load demands. No matter which method was used to construct the Burr-arch truss, Haupt’s 

assertion that continued settlement of the truss led to the arch supporting the majority of the 

dead load later in the life of the bridge remained true.

The interaction between the arch and the multiple-kingpost truss is a curious one, as both systems 

may be used to resist uniform dead loads over the life of the bridge, but neither system is stiff enough 

to effectively resist asymmetric, concentrated (live) loads, particularly not the arch (figure 5.10). 

Thus, the two systems—arch and truss—must work together to support the live load. A modernday likeness to the Burr-arch truss, which also requires the interaction of two systems to support 

the live load, is the deck-stiffened arch. David Billington, professor emeritus from Princeton 

University, described the role of the deck in this system as providing “such a great resistance that, 

in effect, as the arch tries to lift on the right [due to the live load on the left], the deck reacts and 

produces forces in the vertical members that push the arch back down, thus drastically reducing 

the deflection and producing nearly uniform forces on the arch.”13 The stiffening truss in the Burrarch truss performs a similar function to the deck described by Billington: while the left side of 

the truss may be affected by the asymmetric live load producing tension in the diagonal braces, 

the right side is not. Its braces are in compression as a result of the live load, providing additional 

stiffness with which to prevent the upward defection of the arch (figure 5.10).

Figure 5.10 Deflected shape of an arch under a concentrated live load force applied near the quarter-point of the span.

Image generated in Mastan-2 by Rachel Sangree, 2014.
124 Covered Bridges and the Birth of American Engineering

While the Burr-arch truss performed well and was widely constructed, it did have some drawbacks; 

namely, it required large timbers and skilled craftsmen to construct intricate traditional timber joinery. 

And the arches, while providing a critical function, were a challenge to maintain as they were the 

closest members to the waterway and were therefore vulnerable to decay and flood damage. The next 

significant truss design was patented by an architect who was aware of these problems and sought to 

provide an alternative to Burr’s popular form.

Town Lattice Truss

Following the award of a patent to the well-known New England architect Ithiel Town in 1820, wooden 

lattice trusses became a standard in American bridge building. As a result, lattice trusses, whether they 

followed Town’s patent or not, are often called Town lattices. In fact, most of the wooden lattice trusses 

in America probably were built following Town’s 1820 and 1835 patents, which featured lattices and 

horizontal chords of 3 x 10 inch or 3 x 12 inch wooden planks and treenails to connect the members. Other 

lattice forms, patented and constructed in the United States and abroad by others, will be discussed later. 

Ithiel Town completed his first significant work of architecture—Center Church in New Haven, 

Connecticut—in 1814. Briefly diverging from architecture, Town joined fellow New England 

architect Isaac Damon in 1816 to build Burr-arch truss bridges over the Connecticut River at 

Springfield (1816), Northampton (1817), and Hartford (1818). The Hartford Bridge, with its 

counterbraces and superimposed arches, resembled Burr’s Waterford Bridge, completed in 1804.14

Town’s experience constructing the Burr-arch trusses over the Connecticut River left him critical 

of the technology: 

The original mode of using the arch, by Burr, Wernwag, Field, and many others, it 

must be admitted, had the very important advantage of sustaining the most important 

portions of the strain, in the direction of the length of the materials, as in the archpieces, which, indeed, were the main support of the structure. In these constructions, 

in which the arch is so conspicuous for the strength and beauty of the superstructure, 

(for beautiful, it must be admitted the arch is, when applied with good taste,) there 

seem to be evils too great to be overcome, by the most profound science, or the most 

refined practical experience in execution.15

Town identified four issues. First, the cost of these bridges was so great that they could be justified 

only in the most exceptional cases. Second, the horizontal thrust of the arches increased the size 

and cost of abutments; additionally, Burr-arch trusses required such large timbers that they were 

susceptible to dry rot. Finally, the bases of the arches extended below the bridge floor into the 

abutments, leaving these critical members subject to weathering and decay.

After completing the Connecticut River bridges, Town spent time building bridges in the Carolinas, 

possibly experimenting with an improved form. Some of his works include the Yadkin River Bridge 

(1819), the Cape Fear Bridge (1820), and the South Yadkin River Bridge (1825).16 Town was residing 

in Fayetteville, North Carolina, when he received his first patent on January 28, 1820. This patent 

(figure 5.11) described the principles of his truss:
The Development of the American Truss 125

Suppose a vertical plane against 

the side of which are placed the 

sides of a number of equal and 

similar flat pieces of timber or 

other substances of suitable 

dimensions in such manner as 

that they shall be parallel to 

each other, say between two 

horizontal lines in the plane 

and inclined so as to make an 

angle with the horizontal lines 

of about 45° or any angle that 

may be necessary for a brace (as 

they do the office of a brace) 

after which place another series 

of timbers or other substances 

of equal dimensions, distance 

apart and inclination to the 

horizontal lines in the same 

manner and between the same 

parallels into equal diamonds and half diamonds. Hence the longer the pieces are in 

proportion to the distance between them, the smaller will be the diamonds the more 

times each piece in one series will be crossed by those of the other series, consequently 

the greater number of joints, and therefore the more strength and less strain upon each 

joint when weight or power is applied.17

Figure 5.11 Ithiel Town, drawing of a single lattice truss accompanying 

U.S. Patent No. 3,169X, January 28, 1820.

The undeniable advantages the Town lattice truss possessed over the Burr-arch truss included 

its simple, repetitive form, relatively light timbers, and the absence of any traditional joinery. 

Furthermore, the arrangement of lattice members and their connection with treenails eliminated the 

need for an arch. The Town lattice, however, had its own share of problems. Lewis Prevost, a civil 

engineer operating in Massachusetts, observed that the truss tended to settle over time, a condition 

caused both by crushing of the treenails, which were loaded perpendicular to the direction of grain, 

and the tendency of the lattice members to split near their ends.18 Prevost also noted that contact 

between adjacent lattice members accelerated decay. Carl Culmann, who published a German paper 

on American bridges following an 1849–50 tour of the United States, was also critical of the Town 

lattice’s use of “wooden nails,” calling them a “poor means of attachment.”19

Herman Haupt provided a detailed review of the Town lattice in his 1851 book, The General Theory 

of Bridge Construction, although he did not use Town’s name. While Haupt praised the truss for 

its simplicity of form and economic use of material, he thought it should be limited to light loads 

and small spans. A significant problem was the truss’s tendency to warp, which Haupt compared 

to a thin, unsupported plank of wood loaded on its narrow face. A beam loaded in this way fails 

due to what is called lateral torsional buckling: the top of the beam is in compression and buckles 

out of the plane of bending (laterally) while the bottom of the beam is in tension and thus not 
126 Covered Bridges and the Birth of American Engineering

subjected to buckling. This unbalanced loading 

between the top and bottom of the beam causes 

rotation in addition to translation (see figure 4.17 

in chapter 4). Haupt noted that a second defect 

common to the Town truss occurred at the lattice 

ends. The shear forces at the ends of a bridge 

were at a maximum value, but the outermost 

lattice members were truncated and did not 

span between the top and bottom chords. To 

provide sufficient shear resistance, Town lattice 

bridges had to be extended well past the face of 

the abutments. Instead of extending the lattice, 

it was common to provide bolster beams—short 

wooden beams that extended toward mid-span 

under each lattice end. Like Haupt, Theodore 

Cooper criticized Town trusses in his 1889 

survey of American wooden trusses, noting that 

the “thinness of the web system” allowed warping 

and that, through time, the trusses “became 

very flexible, owing to the want of rigidity of the 

treenail connections.”20

Robert Fletcher, a professor of civil engineering at 

Dartmouth College, and J. P. Snow, a consulting 

engineer who specialized in railroads, were 

champions of the Town lattice truss, and Snow 

constructed many of them on the Boston and 

Maine Railroad. Both men took exception to 

Cooper’s remarks regarding the lattice truss 

in their 1932 History of the Development of 

Wooden Bridges, arguing that the omission of 

effective transverse bracing details from many 

published drawings of Town lattice trusses 

would naturally have led to unsatisfactory 

warping “and getting out of line.” In contrast, 

Fletcher and Snow presented a Town lattice 

truss cross-section with transverse bracing 

added that was similar to the Howe trusses 

built on the Boston and Maine (figure 5.12b).21

Town himself recognized the shortcomings 

in his 1820 patent. In 1835, he was awarded 

a second patent for a double-lattice truss with 

additional chords intended to stiffen the truss 

Figure 5.12 Town lattice truss cross-section from

Top: 5.12a) Cooper “American Railroad Bridges,” plate X; 

Above: 5.12b) Robert Fletcher and J. P. Snow, “A History of the 

Development of Wooden Bridges,” Paper No. 1864, Transactions of the American Society of Civil Engineers 99 (1934): 334.

Figure 5.13 Drawing accompanying Town’s 1835 patent for

“An Improved Lattice Truss.”
The Development of the American Truss 127

and decrease its tendency to warp (figure 5.13). It was, he asserted, “an entirely different bridge—one 

in which the materials are so arranged as to produce far greater strength, rigidity, and permanence, 

in proportion to the quantity of materials, and to be far more secure against its trusses twisting, 

leaning sideways, or curving in the direction of their length.”22

The double-lattice truss was typically used on railroad bridges. The Boston and Maine Railroad 

used the Town lattice design extensively, even through the turn of the twentieth century, but lattice 

trusses were also built on the Philadelphia and Reading Railroad and the New York and Harlem 

Railroad.23 Yet, even the double lattice had its critics. Herman Haupt, in particular, devoted a good 

deal of space to criticizing them in his General Theory of Bridge Construction:

Whilst the weight of the timber from the ties and braces has been doubled, the cross-section 

of the chords has been only increased one-half. A great load of unnecessary timber is placed in 

the centre, where any weight acts with the greatest leverage, and produces the greatest strain. 

It is probable that this truss, as usually constructed, possesses less absolute strength with a 

given quantity of material than any other in common use.24

Modern engineers have echoed Haupt’s sentiment that “unnecessary timber” lay at the center of the bridge.25

Figure 5.14 J. P. Snow built 

the double-web Town lattice 

Contoocook Bridge (1889) 

in Merrimack County, New 

Hampshire, one of eight 

surviving covered rail road 

bridges. HAER NH-38, sheet 1, 

Amy James, delineator, 2003.

Other Lattice-Type Bridges in the U.S. and Abroad

Town was more of a salesman than a 

builder, spending a great deal of time 

promoting his truss with his famous 

pitch, “Built by the mile and cut off 

by the yard.” Royalties paid to Town 

for constructing a bridge based on his 

patent were a dollar a foot—unless 

someone was caught building the bridge 

without paying, in which case the royalties were doubled. Town’s ability to promote his design 

may have overshadowed other lattice-type bridges that were built in the nineteenth century. Maine 

bridge engineer and historian Llewellyn Edwards claimed that an unknown builder constructed 

several similar bridges over Otter Creek in Vermont in 1813, predating Town’s patent and even 

Figure 5.15 Herman Haupt’s concept to improve the lattice truss 

was to eliminate warping by orienting the members vertically rather 

than at an angle. Haupt’s truss design, from The General Theory of 

Bridge Construction (New York: D. Appleton and Co., 1851), 153.
128 Covered Bridges and the Birth of American Engineering

his experimentation with the lattice form. Herman Haupt patented a version of a lattice truss in 

1839 to eliminate warping by orienting the ties vertically rather than at an angle (figure 5.15). 

Most of the diagonal members also met at the end “post,” concentrating the reaction force rather 

than distributing it as in the Town lattice. The Bunker Hill Bridge in North Carolina is the only 

surviving example of Haupt’s “improved” 

lattice truss (figure 5.16). New England bridge 

builders Bela Fletcher and James Tasker built two 

variations of Town’s lattice in 1866 by using 6 x 

8-inch timbers for the lattice, notched and bolted 

together, rather than Town’s 3-inch planks. One 

of their bridges was the Pompanoosuc Village 

Bridge in Windsor County, Vermont; the other, 

which currently holds the record for the longest 

historic covered bridge in the United States, is 

the Cornish-Windsor Bridge between the towns 

of Cornish, New Hampshire, and Windsor, 

Vermont (figure 5.17). Still, testifying to Town’s 

influence and ability as a salesman, the bridge is 

often referred to as a Town lattice truss.26 

Figure 5.16 The only surviving historic Haupt truss is the Bunker Hill Bridge in Catawba County, North Carolina.

HAER NC-46, sheet 3, Richard K. Anderson, Jr., delineator, 2004.

Figure 5.17 A detail of the squared-timber lattice truss on

Bela Fletcher and James Tasker’s Cornish-Windsor Bridge 

(1866). The 6 x 8-inch timbers were connected at each 

joint by a notch and a single bolt instead of a pair of treenails. HAER NH-8-10, Jet Lowe, photographer, 1984.

While timber lattice bridges like Town’s were built extensively in the United States, where timber was 

plentiful and cheap, Europeans built lattice trusses (called lattice girders or trellis girders) from iron. 

George Smart patented an iron lattice truss in England in 1822, just two years after Town’s single 

timber lattice, but there is no record of an iron lattice being constructed using Smart’s design.27 Instead, 

Sir John Benjamin MacNeill is credited with introducing the iron lattice to the British Isles in the 

early 1840s, building an 84-foot iron lattice over the Dublin and Drogheda Railway at Raheny, near 

Dublin, Ireland, and later a 140-foot iron lattice over the Royal Canal at Dublin to carry the Dublin 

and Drogheda Railway. Moorson built another well-known iron lattice truss for the Birmingham and 

Gloucester Railway. Several mid-nineteenth-century British authors credited Town with the original 

lattice truss, but this may be a result of Town’s travels through Europe in 1829, during which he “seized 

the opportunity to publicize his 1820 patent truss,” carrying with him copies of his 1821 pamphlet.28
The Development of the American Truss 129

Analysis of Lattice Trusses

Town provides no guidance in his pamphlets as to how a builder might analyze one of his lattice 

trusses. In 1839, he reproduced, almost word for word, a description prepared by Olinthus Gregory 

in 1825 on the use of a scale model to predict the strength of a full-sized structure. While Gregory 

referred to “Mr. Smart’s Patent Mathematical Chain Bridge,” Town eliminated any reference to 

George Smart. Town’s description was not original, but it is likely he used models to assess the 

strength of his patent bridges, having sent Eli Whitney one such scale model around the time of 

his first patent. Gregory explained that strength does not scale 1 to 1 to size. That is, if the length 

of the bridge is n times the length of the model (and all of the other dimensions are also scaled by 

the same value n), the weight of the bridge will increase as 1 to n3

 while the resistance of the parts 

will only increase as 1 to n2

. Thus, a scale factor existed and had to be accommodated. William 

Humber’s 1857 volume on iron bridges noted tests in Germany which had used scale models to 

compare the behavior of iron lattice girders to plate girders.29

Squire Whipple’s seminal 1847 volume on bridge 

building included a comparative analyses of a 

panelized truss with counterbraces (what he called 

a “cancelled truss”) and a lattice truss (a “double 

cancelled truss”), illustrated in figure 5.18. His 

analyses used equilibrium methods and applied 

a moving live load to determine the maximum 

effect of a concentrated force placed at different 

panel points. He determined that a lattice truss 

was slightly more efficient, and also noted that it 

relied more heavily on members in compression 

than in tension, a preferred system for a wooden 

truss.30

Figure 5.18 Figures accompanying Whipple’s analysis of 

Top: 5.18a) a “cancelled truss” and Above: 5.18b) a “double 

cancelled truss.” From Square Whipple, A Work on Bridge 

Building (Utica, N.Y.: H. H. Curtiss, Printer, 1847), 12 and 14.

Herman Haupt’s 1851 volume provided an analysis for a lattice truss built for the Cumberland 

Valley Railroad across the Susquehanna River at Harrisburg, Pennsylvania. The analysis considered 

the lattice braces terminating at nodes A, b, c, d, e, f, and g, which were all directly supported and 

thus resisted half the weight of the truss (figure 

5.19). Using trigonometry and proportioning the 

brace forces such that the brace terminating at 

A carried a maximum force and the remaining 

supported braces carried some fraction of A, 

Haupt calculated the maximum force in the end 

brace to be approximately one-fifth of the total 

reaction force distributed over nodes A through 

g, approximately 13,125 pounds.31

Figure 5.19 Haupt’s illustration accompanying his calculations

for the maximum force in a lattice brace. From Haupt,

General Theory, 241.

British engineer William Humber’s book on cast- and wrought-iron bridges demonstrated the 

variation in force in the lattice members due to the combination of a uniformly distributed dead 

load and a moving live load. He described the calculations for an iron lattice, but the principle 
130 Covered Bridges and the Birth of American Engineering

was the same for a lattice of wood. His diagram of force variation (figure 5.20) combined the force 

due to a uniformly distributed dead load (shown below line AB) and the force due to a moving, 

uniformly distributed live load (shown above line AB). The sum of both values was indicated at 

discrete locations along the beam by dashed lines (mn).32

Figure 5.20 A graphical representation of the

axial force in lattice members caused by a uniformly 

dis tributed dead load (diagram below AB) and a 

moving, uniform live load (diagram above AB). From 

William Humber, A Practical Treatise on Cast and 

Wrought Iron Bridges and Girders (London, 1857), 96.

Both Burr and Town developed and patented successful truss forms that were widely adopted in 

covered bridges throughout the United States, but, still, neither form provided effective counterbracing 

to stiffen the truss under moving live loads, nor were their designs capable of being adjusted as wood 

viscosity and shrinkage caused the truss to settle over time. Further, for long spans, even the Town 

lattice required a supplemental arch—whose ends, just as in the Burr-arch truss, suffered from 

accelerated decay and degradation. The next two highly successful truss designers, Stephen H. Long 

and William Howe, addressed all of these issues, each one innovating a truss form using the concept 

of prestressing.

Stephen H. Long’s Trusses

Army engineer Col. Stephen H. Long’s interest in bridge design apparently began in 1828 after his 

appointment to the board of engineers for the pioneering Baltimore and Ohio Railroad (B&O). It 

extended to the early 1840s, when he received orders to coordinate navigation improvements on 

the Mississippi, Missouri, Arkansas, and Ohio rivers. Long’s accomplishments over the course of 

his extraordinary engineering service to the country included writing a seminal manual on railroad 

design, making improvements in locomotive design, and inventing improved wood-truss bridges.33

The “Jackson Bridge” and Long’s 1830 Patent

Long designed a new truss bridge in 1828–29 for the B&O, but instead of using it on the main 

line, officials relegated it to carrying a highway over the right-of-way. He named the bridge “Jackson 

Bridge” in honor of President Andrew Jackson because his first assignment in 1816 was in the 

general’s southern division and perhaps because Jackson supported Long’s territorial explorations. 

Long received a patent for his bridge design in March 1830. He published three brief articles in 

the Journal of the Franklin Institute in 1830, which, along with his patent description, provide an 

understanding of his innovations. The bridge was covered and built “on the Washington road, about 

2 1⁄4 miles from Baltimore at its intersection with the Baltimore and Ohio Railroad at an elevation 

40 feet above the latter. The length or span of the bridge is 109 feet, its width from out to out 24 

feet, and its height from bottom to top of its posts, 14 feet.” The bridge was probably very similar 

to that shown in figure 5.21, which is taken from his patent application. Long explicitly stated that 
The Development of the American Truss 131

the “upper arch braces” specified in his patent description were not used in the Jackson Bridge, and 

it seems, with one known exception, they were never used in any bridge built to this design because 

of the practical problems they created for cladding the bridge with wood.34

Figure 5.21 Watercolor of Col. Stephen H. Long’s elevation and plan of 

Jackson Bridge, 1830. Courtesy of National Archives and Records Administration, Cartographic and Architectural Branch, College Park, Md.

Figure 5.22 Long truss connection detail,

showing the diagonals prestressed by a

wooden wedge d. From S. H. Long, Description

of Col. Long’s Bridges, Together with A Series of 

Directions to Bridge Builders (Concord, N. H.: 

John F. Brown, Printer, 1836), plate II, p. 4.

One of the important innovations Long claimed in his patent was the use of counter diagonals 

prestressed by the insertion of wooden wedges, as seen in figure 5.22. The wedges introduced 

compression in both diagonals, eliminating the need for tension connections at their ends. Under 

the action of a moving vertical load, both diagonals were active and contributed to the stiffness of 

the bridge. The ability to re-drive the wedges—thus retightening the bridge—meant that builders 

could use unseasoned, “green” timbers for construction. All the timber in the Jackson Bridge, except 

Figure 5.23 Left: 5.23a) Detail view of one of the wedges hammered into the base of each counterbrace on the Eldean Bridge.

 William G. Keener, photographer, 1998. Courtesy of Ohio History Connection. Right: 5.23b) Interior elevation of Eldean Bridge’s 

Long truss. The wedge connection details are out of view, just below the deck. HAER OH-122-14, Jet Lowe, photographer, 2002.
132 Covered Bridges and the Birth of American Engineering

the keys, was white pine, “with no other seasoning than what it might have acquired in six weeks, 

during which time the work was in progress, having been framed and raised in that time by six 

workmen only.” Long’s design used neither treenails, as in Town’s lattices, nor a supplementary arch, 

as in Burr’s designs. Moreover, the forces in the members were principally in the axial direction 

(along the grain), with minimal bending. Another of Long’s patent claims involved the method of 

splicing the lower tension chords; he patented both iron and wooden fish plates. Most significantly, 

Long used French engineer Claude-Louis Navier’s analogy (see chapter 4) to size the chords of 

the Jackson Bridge, becoming the first American engineer to explicitly state the capacity of his 

design: “Agreeably to the most approved rules for computing the strength of similar structures, it 

will sustain, on every square foot of its floor, in addition to its own weight, at least 120 pounds, or 

equally distributed over the entire surface of its floor, about one hundred and ten tons weight.”35

Because his design approach was based 

on engineering analysis, Long was 

able to compute and publish a table in 

August 1830 that prescribed chord areas 

and the corresponding load capacities 

for a set of simple spans. In the same 

article, Long attempted to explain the 

behavior of the prestressed counter and 

main diagonals, arguing that the stress 

“to which the truss frames are subjected, 

by the heaviest load that is admissible 

upon the bridge, is no greater than that 

exerted upon it without any load at 

all.”36 This was only true for the counters 

that shared in carrying live load until 

all the pre-compression was relieved and 

they became loose. A gravity live load 

did increase the compressive force in the 

main diagonals.

Figure 5.24 One of the original models of the Long truss, used by

Stephen Long’s agents to sell his bridge. Displayed at the New Hampshire 

Antiquarian Society in Hopkinton. Francesco Lanza, photographer, 2003.

Although the B&O chose not to build any railroad bridges using Long’s design, the Jackson 

Bridge was a very important success. Through it, Long convinced his two colleagues on the B&O, 

William Gibbs McNeill and George Washington Whistler—both of whom became influential 

chief engineers for other railroads—of the merits of his design. In 1832, three Long bridges, two 

measuring 70 feet and one measuring 100 feet, were built to carry trains of the Baltimore and 

Susquehanna Railroad. These were probably the first wooden-truss bridges to carry railroad loads 

in the nation. The testimonials appended to Long’s 1836 pamphlet demonstrate the spread and 

influence of Long’s technology throughout the Middle Atlantic and New England states. Thomas 

Hassard received the rights to build Long-truss bridges in Maryland and built nineteen of the type 

for the Paterson and Hudson, Baltimore and Susquehanna, Boston and Providence, and Boston 

and Worcester railroads up to 1836. Long appointed his brother Moses Long as a “general agent”; 

Thomas Hassard and Benjamin Franklin Long, another brother, as “special agents”; and twenty-three 
The Development of the American Truss 133

other men as “subagents” to promote his design. The subagents included Long’s relatives Horace, 

Enoch, and Warren Childs of Henniker, New Hampshire. Moses Long promoted the design by 

mailing broadsides.37

Long’s design performed well and was widely 

accepted by railroads, but it required attentive, 

knowledgeable maintenance as wood viscosity, 

shrinkage, and vibration created the need to 

periodically retighten the wedges. Perhaps the 

weakest aspect of Long’s design was its vertical 

wooden tension members. The gravity loads from 

the floor beams had to be transferred into the 

vertical tension posts at cutouts or shoulders, 

resulting in shear stresses along the dotted lines 

in figure 5.25 that could cause structural failure 

as the wood degraded over time. William Howe 

addressed this weakness in his 1840 patent.

Figure 5.25 The transfer of tension forces into the vertical

members that extended beyond the lower chord of Long’s

1830 patent truss resulted in a detail that was highly susceptible

to shear failures.

Long’s 1836 Patent and Pamphlet 

Long returned home to Hopkinton, New Hampshire, in 1835 and evidently spent some time thinking 

and writing about bridges. He was awarded a new patent on January 23, 1836 (having received 

other patents in 1832 and 1833), and published a pamphlet on bridges, which was republished in 

Philadelphia in 1841. Instead of a new design for the principal load-carrying trusses, Long’s 1836 

patent proposed a system for preventing out-of-plane movements of chords. Long emphasized that 

his object was to “produce and ensure lateral stiffness or inflexibility in wooden or frame bridges.” 

Long must have observed out-of-plane buckling of truss top chords and recognized the importance 

of precluding such failures. His patent was probably the first awarded for a system to provide lateral 

stiffness in wooden bridges.38

Long’s pamphlet described his 1830 and 1836 patents, summarized writings previously published in 

the Journal of the Franklin Institute, and provided a “series of directions to bridge builders.” He also 

commented on gains in structural efficiency from truss designs with chords that were continuous 

rather than interrupted over interior piers. Long called such continuity “double action” and correctly 

noted that such continuity placed the top chords in tension and the bottom chords in compression at 

intermediate supports. He advocated making the end spans three quarters the length of the interior 

spans. Long repeated statements from his August 1830 Journal of the Franklin Institute article that 

the use of prestressed diagonals eliminated increases in the forces from live loads in the diagonals. 

Again, this observation was only true for the counter diagonals. His guidelines for raising a bridge 

and installing the wedges suggested that “the workmen begin at the extremities of the span, and 

proceed towards the center, taking care to drive them as hard as they may be driven, with an axe 

or sledge weighing 4 or 5 pounds.”39

The unique element of Long’s pamphlet was his series of tables prescribing member sizes for truss 

bridges with spans between 55 and 300 feet. These tables extended and elaborated on the table 
134 Covered Bridges and the Birth of American Engineering

published in August 1830. Long used Navier’s analogy and limited the maximum stresses in the 

chords to 2,000 pounds per square inch, half the assumed minimum wood strength, under an 

extremely large, uniformly distributed live load of 120 pounds per square foot. Carl Culmann first 

observed this fact in his extended paper on American bridges published following his 1849–50 U.S. 

tour, an observation that was reaffirmed by new research in the 1980s. Interestingly, Culmann felt 

that the allowable stress of 2,000 pounds per square inchwas “set somewhat too high.” It forced 

Long, Culmann opined, “to assume this abnormally large random loading of 120 pounds per square 

foot, which in reality can never be present.”40

Long’s 1839 Bridge Patents

Long was awarded two additional bridge patents on November 7, 1839. An extended, eight-page 

discussion of the patents appeared that year in the Journal of the Franklin Institute, and a brief 

description followed several years later. The details of the “Wooden-Framed Brace-Bridge” patent 

are largely incomprehensible. The bridge resembles Long’s 1830 design but with added arch-like 

braces, lattice-like member sizes, diagonals connected by treenails, and no wedges for prestressing. 

Long’s motivation for the design is difficult to discern, especially since his other patent, issued at 

the same time, retained the use of wedges and the prestressing concept. Long may have wanted 

builders who added arch-like braces to his 1830 system to pay him royalties. Alternatively, he may 

have observed owners failing to maintain trusses built according to his 1830 patent design, leading 

to the counter diagonals becoming loose and ineffective.41

The second November 1839 patent was for a “Wood-Framed Suspension Bridge” and had diagonals 

with tension connections that were pretensioned by driving wedges between the posts and the 

chords (figure 5.26). This placed the diagonals in tension and the vertical members in compression, 

the reverse of his 1830 truss. The difficulty of achieving good tension connections with treenails 

made the design impractical for wood, although Long included the possibility of using iron for 

the design. A second concept included in this patent was the use of variable panel widths, which 

decreased from mid-span to the abutments, in an attempt to equalize forces in the diagonals. While 

this approach was theoretically correct, the extra detailing and inherent construction challenges 

made the concept impractical. Nonetheless, the two concepts demonstrated Long’s understanding 

of truss behavior and prestressing. 

Figure 5.26 Details from Col. Stephen H. Long, drawing accompanying U.S. Patent No. 1,397, November 7, 1839. 

Note wedges at the top of the vertical members in fig. 2 and the decreasing panel widths in fig. 4.
The Development of the American Truss 135

Long’s Contributions

As the first American engineer to use and disseminate the theoretical developments of Navier, 

Long’s advancement of American truss design was seminal. His 1830 and 1839 patents defined the 

two basic designs for parallel-chord trusses. His contributions, however, are not widely recognized 

because of the rapid changes that occurred in material technology between 1840 and 1870. By 

substituting iron vertical members for wood, William Howe’s 1840 patent facilitated prestressing 

and eliminated the main weakness in Long’s trusses, quickly making Long’s 1830 design obsolete. 

Thomas and Caleb Pratt’s 1844 patent made Long’s first 1839 design practical through the use of 

iron diagonals and counters. 

The most thoughtful scholarship on Long’s work was written by his German contemporary, Carl 

Culmann, following the latter’s American tour. Culmann read Long’s 1841 booklet but never met 

the American. The only Long bridges he examined in person were some railroad bridges in Georgia 

“that were close to collapse,” apparently from lack of maintenance. Culmann devoted many pages of 

his paper to analyzing Long’s designs and included two full plates with nineteen drawings containing 

numerous important details. In addition, Culmann reproduced portions of Long’s tables and proved 

that Long calculated chord forces using Navier’s analogy. He showed that chord areas for the entire 

range of spans were such that the maximum normal stress was 2,000 pounds per square inch for 

a uniformly distributed live load of 120 pounds per square foot. Culmann also recognized the 

differences between Long’s 1830 and 1839 patents and admired Long’s stiff patented lateral bracing 

system. He also found problems with Long’s designs, noting that the wedges were soon loose and 

that the use of treenails in the 1839 patents was a “very poor means of attachment.” Ultimately 

though, Culmann described Long as “surely one of America’s most intelligent and well-educated 

engineers, and bridge construction in this country owes much to him. It can be gleaned from his 

designs that he was well aware of the effects of various forces in the interior of the structure, and 

knew how to deal with each of them in a suitable manner.”42

Culmann observed that Long’s trusses fell from favor with American railroads as iron and steel 

construction replaced wood and as newer truss designs by Howe and Pratt became prominent. 

Long’s contributions were further obscured by the American transition in the 1870s to statically 

determinate forms without counter-diagonals for both Howe and Pratt trusses. As a result, most 

twentieth-century commentators did not give Long as much credit as Culmann had and failed to 

place Long’s designs in the context of Howe and Pratt trusses. The comments of the late bridge 

historian John G. James are the most unfair. He wrote that Long “produced a stream of patents and 

pamphlets which have left his name far more well-known in bridge history than his engineering 

activities justify.” Claiming it was “difficult to see that Long contributed anything of material value 

to wooden truss development,” James also demeaned Long’s patent enforcement against Nathaniel 

Rider, who had simply copied Long’s first 1839 patent (no. 1,397). Apparently not comprehending 

the effects of prestressing in two of Long’s patents, James was baffled by how Long intended to insure 

that the members in his trusses performed in accordance with his patent designs. Most egregiously, 

James completely ignored the significance of Long’s tables. James’s opinions on Long’s contributions 

were a great injustice and damaging to an understanding of American wooden-truss bridge history.43
136 Covered Bridges and the Birth of American Engineering

The Howe Truss

The arrangement of members shown in figure 5.27 is known as a “St. Andrew’s cross.” Because it 

resembles a Howe truss, it is logical to consider this ancient form first. Marc Seguin used the St. 

Andrew’s cross design shown in figure 5.27 as a stiffening truss in his Tournon-Tain suspension 

bridge in 1824, sixteen years before the Howe patent.44 The nut below the floor beam was used 

to pre-compress the diagonals and “tighten” the truss. Described and illustrated by European 

engineers in the 1820s, the design was used in 

other French suspension bridges, most notably 

by Joseph Chaley for his 1834 Grand Pont 

Suspendu at Fribourg, Switzerland. Chaley’s 

stiffening truss was described in an 1835 issue of 

the Journal of the Franklin Institute: “On both 

sides . . . are strong oaken balustrades, made in 

the form of St. Andrew’s cross, the height of 

which is four feet.”45 John Roebling likely came to 

know Seguin’s stiffening truss design from Carl 

Berg’s 1824 book Der Bau der Hangebrucken 

aus Eisendraht, which was available during his 

studies in Germany. Roebling’s competitor, 

Charles Ellet, studied suspension bridges in 

France from June 1830 to 1832 and became a strong advocate of them. Ellet’s 1839 pamphlet on 

suspension bridges commented on Navier’s 1823 analysis of suspension bridges and on those bridges 

at Tournon-Tain and Fribourg; furthermore, his 1840 and 1841 designs for suspension bridges at St. 

Louis and Philadelphia both made use of St. Andrew’s cross trusses. This clearly shows that American 

suspension-bridge designers knew of the St. Andrew’s cross truss design before the Howe patent.46

Figure 5.27 St. Andrew’s cross truss. Redrawn from Marc Seguin,

Des ponts en fil de fer, 2d ed. (Paris: Chez Bachelier, Libraire, 1826),

figure 9, plate 2.

American engineers embraced wood trusses, especially Long’s truss, for railroad bridges. In 1840, 

while the Western Railroad (later the Boston and Albany Railroad) was being built from Springfield, 

Massachusetts, to the state line at West Stockbridge, William Howe was apparently motivated to 

design a new truss, superior to Long’s, to compete for the lucrative business of building bridges. 

Howe received two patents in 1840. The first, no. 1,685 (figure 5.28), was an entirely wooden truss 

that used wedges, but in a different manner from Long’s design. The drawing shows diagonals 

spanning two panels, as defined by the vertical members.47 The second patent, no. 1,711 (figure 

5.29), was Howe’s design for a combination wood-iron truss. In place of wedges, it used tightening 

nuts on threaded vertical iron rods to post-tension the structure. 

Figure 5.28 Redrawn from William Howe, drawing accompanying U.S. Patent No. 1,685, July 10, 1840.
The Development of the American Truss 137

Figure 5.29 William Howe, drawing accompanying U.S. Patent No. 1,711, August 3, 1840.

Howe’s solitary claim in patent no. 1,711 was the combination of iron bolts and wooden blocks 

“against which the braces and counter braces abut, so as to cooperate in increasing the camber to 

any desired extent.” The text for this patent referred to the “truss-frame” of his earlier patent but 

indicated that it had been “deemed expedient to separate it therefrom, and make it the subject of 

a distinct patent.” By adding vertical iron rods, Howe eliminated the principal weakness of Long’s 

design and made truss tightening much easier. Howe’s design made Long’s obsolete, even though 

the behavior of the two trusses, with diagonals spanning only one panel, was essentially the same.48

Setting aside the fact that Howe’s 

patent drawing showed diagonals 

spanning over two panels, did 

significant differences exist between 

Howe’s design and the St. Andrew’s 

cross? An important distinction 

lay in the use of wooden blocks, 

or bearings, that were keyed in the 

chords as shown in figure 5.30. 

The keying allowed the transfer of 

any unbalanced horizontal force 

components from the diagonals into 

the chords, which was necessary to 

achieve truss action. Neither the 

European drawings from the 1820s nor those in Ellet’s 1840 pamphlet show keying of the diagonals 

into the chords.49 Without keying, there is only the friction at the interfaces between the diagonals 

and the chords to make a St. Andrew’s cross behave as a true truss. Moreover, the extension of 

the bolt through the floor beam in the St. Andrew’s cross form increased the probability that the 

diagonals would become loose due to wood viscosity and shrinkage. The wood node blocks in the 

Howe design also allowed the diagonals to have simple square ends, assuring axial stresses in the 

along-grain direction of the diagonals.

Figure 5.30 In the Howe truss node Left: (example 5.30a, based on the 

Moose Brook Bridge nodal casting), the iron casting was keyed into the chord, 

allowing unequal horizontal components of the forces in the diagonals to be 

transferred into the chord. Without this casting, the St. Andrews cross node 

Right: (example 5.30b) had only limited truss action and a high probability of 

becoming loose through time.

The Western Railroad and International Dissemination

William Howe had the foresight and good fortune to develop his truss in conjunction with the 

building of a critically important American railroad, the Western Railroad. In October 1836, 

the railroad hired West Point graduate and former topographical engineer George Washington 

Whistler, who became chief engineer for the railroad in 1840, serving until 1842. His engineering 
138 Covered Bridges and the Birth of American Engineering

leadership resulted in the Western Railroad being labeled “Whistler’s railroad.” He can be credited 

with the incredibly rapid national and international adoption of the Howe truss because, following 

Howe’s successful erection of a small bridge for the railroad, Whistler awarded Howe and Howe’s 

brother-in-law, Amasa Stone, the prized contract for the Connecticut River Bridge at Springfield. 

Howe had been working with Stone since 1836, principally building churches and dwellings near 

Warren, Massachusetts.50 They continued their collaboration by successfully completing the bridge, 

shown in partial elevation in figure 5.31, in the summer of 1841.

Figure 5.31 Partial elevation of the 

Western Railroad Connecticut River 

Bridge at Springfield. The “inferior 

arch braces” were soon recognized 

to be unnecessary and thus were not 

commonly used. From Lewis M. Prevost, 

“Description of Howe’s Patent Truss 

Bridge,” Journal of the Franklin Institute

3, no. 5 (May 1842): 291. Courtesy of 

George Peabody Library, The Sheridan 

Libraries, Johns Hopkins University.

The Western Railroad’s 1842 annual report provided a detailed assessment of the bridges on the road.

The railroad bridges east of the Connecticut River are constructed of truss frames, after 

the plan of Long’s patent, and are made for two tracks. The Connecticut River Bridge, 

and those westward of it, on the Western road, are of truss frames, of Howe’s more recent 

patent, and they are constructed for one track only. The truss frames of all are covered in 

on the sides and top, and thoroughly white-washed. The entire floor of the Connecticut 

River Bridge is covered with tin, painted of a dark color. This bridge is 1,264 feet long, of 

7 spans, 180 feet each. The whole length of wooden superstructure of bridges is 6,092.5 

feet or 1 mile, 812.5 feet and they are in number 48, both exclusive of road bridges over 

the railroad.51

The reports also indicated that the West Stockbridge and Albany Railroad had seventeen wooden 

Howe trusses, all covered and whitewashed, two of which had spans of 160 feet.52

Almost overnight, Howe’s design had made Long’s truss obsolete, leading to a frenzy of Howetruss railroad-bridge construction in the fall of 1841 and throughout 1842. A biographer in 1869 

indicated that much of this work fell to Stone. The winter of 1841 was “most trying and arduous. 

About a thousand lineal feet of bridging on the Western Railroad, in the Green Mountains [the 

Berkshires] had to be completed, and Mr. Stone and his men were called upon to carry the work 

through.” No doubt convinced of the superiority of the Howe design, Stone formed a partnership 

with Azuriah Boody and, in 1842, purchased Howe’s bridge-patent rights for the New England 

states, “including all improvements and renewals,” for $40,000. Boody, Stone, and Company was 

among the early bridge companies devoted to the design, fabrication, and erection of bridges in 

the United States.53
The Development of the American Truss 139

Lewis M. Prevost’s 1842 illustrated article on the Connecticut River Bridge emphasized that “the 

stress comes upon the end grain of the main and counterbraces, and is in the direction of their 

length—consequently there is not the same danger of the settling which occurs in lattice bridges, 

in consequence of the crushing of the pins and the splitting of the lattices at their ends—and there 

being a free circulation of air between the main and counterbraces, the bridge is not as liable to the 

speedy decay which occurs in lattice bridges, wherever the lattices come in contact.” He concluded 

“that in bridges with spans equal to, or exceeding, those of the bridge at Springfield, the peculiar 

truss above described, will be found superior in strength, stiffness, and durability, to those of Town’s 

double lattice plan.” The editors of the American Railroad Journal agreed, insisting in 1844 that 

Howe’s was “the best patented American bridge.” Howe’s design became the most widely used 

bridge form during the railroad building mania of the 1840s, 1850s, and 1860s.54

After Howe-truss bridges were in service for some time, however, a flaw in the design became 

apparent. Rod forces decreased due to viscous wood behavior, wood shrinkage, and crushing on the 

chords under the vertical rod plates, frequently resulting in a looseness in the counter diagonals and 

reductions in stiffness. Stone recognized the problem and anticipated the unacceptable possibility 

of failure. After a sleepless night in which he nearly exhausted his “inventive thoughts,” an idea 

occurred to him for “a better combination of the Howe bridge, but would not in principle be 

improved upon. Sleep immediately came.” The next day, using models to prove the ideas to his 

satisfaction, he adopted them as his standard design.55 Stone’s improvements probably included an 

iron nodal casting with a sleeve extending through the chord thickness. It was, however, Howe who 

in 1846 received a patent for such a design.56 Howe either simply patented Stone’s ideas, devised the 

improvements independently, or reached an agreement with Stone to file the patent in Howe’s name, 

since “all improvements and renewals” were part 

of Stone’s purchase. The iron nodes and singlepanel diagonals came to define the “classic” 

Howe form. The first use of these improvements 

is unknown. Richard Osborne designed all-iron 

Howe trusses with single-panel diagonals in 

1845, and Frederick Harbach patented a similar 

all-iron Howe truss in 1846, making it likely that 

classic Howe trusses were in use before 1845. By 

1877, Stone claimed to have constructed “from 

ten to fifteen miles in length of Howe bridges.” 

He must have been the most prodigious builder 

of Howe bridges in history.57

In addition to revolutionizing American bridge 

building, the Connecticut River Bridge became an international engineering sensation. After being 

personally recruited by two Russian engineering officers representing Czar Nicholas I, Whistler 

resigned from the Western Railroad in May 1842 to accept the post of consulting engineer for the 

St. Petersburg–Moscow (or Nikolaev) Railway. While en route to Russia, Whistler traveled through 

London and provided drawings of the Connecticut River Bridge to publisher John Weale, who 

included the drawings in his 1843 volume on stone, iron, timber, and wire bridges.58 After arriving 

Figure 5.32 Casting with sleeves that transferred rod tension 

forces directly into the casting without causing bearing stresses in the chords and possibly crushing them. Found on the 

Rexleigh Bridge, a Howe truss dating to 1874 in Washington 

County, New York. Dario Gasparini, photographer, 2011.
140 Covered Bridges and the Birth of American Engineering

in Russia, Whistler made recommendations on the road’s alignment, the gauge of the rails, rolling 

stock types, and bridge forms. His recommendation to employ wooden Howe-truss bridges was fully 

embraced, and about sixty were built along the nearly 400-mile Nikolaev Railway before 1851. The 

grandest were the Msta Bridge, shown in figure 5.33a, which had nine continuous 177-foot spans, 

and the very similar Verebia Bridge, designed in partnership with the brilliant Russian engineer D. 

I. Jouravsky (or Zhouravsky), with nine continuous 200-foot spans. 

Figure 5.33 Examples of George Washington Whistler’s Howe truss bridges on the St. Petersburg–Moscow (Nikolaev) Railway, ca. 1860.

Above top: 5.33a) is the nine-span, 1,600-foot Msta Bridge; Above: 5.33b) is the three-span Tverca River Bridge. Courtesy of DeGolyer

Library, Southern Methodist University, Dallas, Texas, Views of the Nikolaev Railway.

Jouravsky studied Howe bridges using physical models and developed mathematical methods of 

structural analysis. He considered continuity and post-tensioning forces from tightening the iron 

rods. He published his work in a book, won the Demidoff Medal in 1855, and later published in 

the Annales des Ponts et Chaussees.

59

Engineer Carl Ritter von Ghega (or Carlo Ghega) also disseminated the Howe bridge form in 

Europe. Following an 1842 study tour of American bridges, he published a book of observations and 
The Development of the American Truss 141

analyses. He explicitly illustrated and discussed the Connecticut River Bridge and offered extensive 

comments on the Howe form; in fact, the phrase “Howe’shchen Brücken” (“Howe’s bridges”) is 

part of his book title.60 Ghega’s pioneering work likely influenced Carl Culmann’s own paper on 

American wooden bridges; Culmann wrote, “this design is the best known and widely employed 

here in Europe, particularly in Austria,” and felt no need to devote space to explaining the type.61

Culmann did illustrate a Howe bridge over the Chicopee River in Connecticut which had diagonals 

spanning only one panel and carefully discussed the details of the iron node castings. Clearly, 

Howe’s design was recognized as distinct from the St. Andrew’s cross truss and was widely used in 

Europe in the 1840s. Two Howe bridges remain in Bavaria dating to the 1850s whose form is very 

similar to the Connecticut River Bridge, although they have iron nodes.62

Structural Behavior of Howe trusses

The classic Howe truss was a post-tensioned, statically indeterminate system. The post-tensioning 

eliminated the need to design tension connections for the diagonals. The design did not use treenails 

to transfer forces, and the member stresses were in the direction of the grain. Only minimal wood 

joinery was required, primarily in the bottom chord tension splices. 

Because the Howe truss was statically indeterminate, nineteenth-century designs must have been 

based on simplified analyses using only equilibrium equations. The chords of Howe trusses were 

commonly designed using Navier’s analogy of a truss as a beam, exactly as Long had done; the forces 

in the diagonals were generally understood to increase from midspan toward the ends. Therefore, 

the sizes of the diagonal members, as well as the sizes of the iron rods, increased from midspan 

to the supports. (The ability to use joint-by-joint equilibrium to determine forces in the diagonals 

of statically determinate forms became common only in the 1870s, when the Pratt truss became 

dominant for all-metal designs.) Counters were understood to be needed near midspan, where 

“reversals of the direction of shear forces” could occur under heavy moving live loads. Counter 

diagonals were also understood to contribute to stiffness and to be necessary if “tightening” or 

post-tensioning was to be done. Because it was not possible at this time to predict forces from posttensioning, these forces were generally ignored. 

Unfortunately, the construction techniques used to build classic, statically indeterminate Howe 

trusses are now largely forgotten. However, an 1853 document describing the construction of a 

200-foot Howe railroad truss illuminates the methods used to achieve camber and to tighten the 

truss. The camber criterion was apparently based on modeling the top and bottom chords as arcs 

of circles with radii of curvature differing by the depth of the truss. With a prescribed camber, the 

difference between the chord arc lengths in one panel was computed. This difference was then used 

to define an upper-chord panel length that was slightly longer than the lower chord. This placed the 

iron rods in a radial rather than exactly vertical orientation. Rods were tightened using a wrench 

“with about a two feet leverage” beginning at the ends of the bridge and working toward midspan. 

Some retightening was likely required after a period of service. Ole Haldorson, a highway bridge 

builder who worked in Oregon during the 1930s and 1940s, indicated that adjusting the tension 

rods in Howe bridges “was something we did” a year or two after the completion of a bridge. “From 

then on, you could go out every ten to twelve years before retrussing [re-tensioning].”63
142 Covered Bridges and the Birth of American Engineering

The effects of post-tensioning and the linear elastic behavior of classic Howe bridges under moving 

loads may now be easily estimated using computer-based structural analysis programs, as was done 

during the HAER documentation of the Pine Bluff Bridge in Indiana in 2002.64 Wood is, however, 

a viscous, hygroscopic material whose behavior depends on moisture content and is a function of 

time. Therefore, linear elastic models are not sufficient for predicting the full range of structural 

behavior in a wood structure. Moreover, truss design based on linear elastic load effects and element 

design provides only a lower bound for the actual strength or capacity of a real truss.

The classic Howe truss had diagonals and counter diagonals and was pre-tensioned. But statically 

determinate versions of the Howe truss, without counters, were also commonly built. Such designs 

with wooden verticals were sometimes called multiple-kingpost trusses, but structural engineers do 

not use this terminology. Single-diagonal Howe trusses could not be post-tensioned. They also could 

not accommodate reversals in panel shear forces unless the main diagonals were detailed with end 

connections that could transfer tension. 

In many ways, the Howe truss and wood were an ideal combination. Pre-tensioning eliminated most 

tension connections except in the chords, and, although the main diagonals acted in compression, 

the sizes of the wood members were such that the allowable compressive stresses were not limited 

by buckling. For the more slender members that resulted from steel construction, the Pratt truss 

was definitely a more suitable form.

The Pratt Truss

The truss patented by Thomas Willis Pratt and his father, Caleb, made Long’s 1839 suspension truss 

practical because it utilized wrought-iron rods for the tension diagonals. Thomas Pratt was born in 

Boston in 1812 and studied architecture at the Rensselaer School in Troy, New York. His professional 

career was spent principally with several Massachusetts railroads.65 As a New England railroad bridge 

designer, he would have known Long’s 1830 and 1839 designs and Howe’s 1840 improvement. He 

patented his truss in 1844 while working on the Norwich and Worcester Railroad (figure 5.34). 

Figure 5.34 Thomas W. Pratt and Caleb Pratt, drawing for U.S. Patent No. 3,523, April 4, 1844.
The Development of the American Truss 143

Pratt’s patent description demonstrated a thorough understanding of his invention’s structural 

behavior. His statement that a “series of vertical posts . . . is elevated, the same resting upon shoes,” 

implied that the verticals were not meant to be connected to the chords. Pratt correctly identified 

the members he labeled D on his patent drawing as “main braces” and those labeled E as “counter 

braces,” exactly opposite to the roles of the same diagonals in a Howe truss. He also understood the 

effect of tightening the wrought-iron diagonals, stating that “they draw or confine the posts and 

stringers together.” He relied on the compressive 

pre-load in the posts to keep them in position. 

The only differences between Pratt’s design and 

Long’s 1839 design were the elimination of 

wedges on the verticals, and the use of wroughtiron diagonals in place of wood.66 The prestress 

conditions in Long’s 1830 and 1839 patented 

trusses are compared with Howe’s 1840 design 

and Pratt’s 1844 design in figure 5.35. 

A comparison of the Howe and Pratt trusses from 

a variety of engineering viewpoints is both interesting and informative. The Pratt truss used twice 

as many diagonal rods as the Howe, and required them to be of wrought iron, the more expensive 

material in the mid-nineteenth century. The Pratt truss also required tensioning more diagonals. 

Increasing the size of the wrought-iron vertical components in a Howe truss could be done more 

easily than putting larger iron diagonals in a Pratt truss. It is likely a variable-depth truss could be 

more readily constructed in a Pratt form, as shown in the patent drawing. As indicated in figure 

5.35, prestressing a Howe truss increased the gravity load tension in the bottom chord and decreased 

the gravity load compression in the top chord, while just the opposite was true in a Pratt truss. A 

Pratt truss’s compression verticals were shorter than the compression diagonals of a Howe truss, 

but member buckling did not commonly determine the dimensions of a Howe’s wooden diagonals. 

Bearing stresses were perpendicular to the grain of the chords in both designs, but the use of cast-iron 

nodal sleeves could minimize them in a Howe. Transferring unbalanced horizontal components of 

force into the chords at each truss node required notching the chords in both designs. A less evident 

difference was the “out-of-plane” stability of each truss panel during prestressing. The Howe-truss 

panel had no tendency to warp during prestressing and was, therefore, more stable. When a Pratt 

panel was prestressed, it was unstable out-of-plane. As a result, in wood-iron combinations the Howe 

truss was the more suitable form, as demonstrated by the dominance of the Howe truss for early 

railroad bridges. The relative advantages of the two forms were reversed for subsequent all-iron or 

all-steel bridges, where member stability was a governing design criterion.67

Bridge designers in the second half of the nineteenth century faced a choice of truss forms and had 

to consider how particular forms led to distinctly different structural behaviors. In brief, a designer 

could decide to use a form with no counter diagonals, a form with non-prestressed counter diagonals, 

or a form with prestressed counter diagonals. 

Forms with no counters—If no counters were used, the basic Howe and Pratt trusses were 

statically determinate and could not be prestressed. In general, the main diagonals were sized 

Figure 5.35 Left: 5.35a) Initial prestress forces in Long’s 1830 

patent truss and in a Howe truss; Right: 5.35b) initial prestress 

forces in Long’s 1839 patent truss (no. 1,397) and in a Pratt truss.

Thick red lines = compression, thin blue lines = tension.
144 Covered Bridges and the Birth of American Engineering

and connected to take both tension and compression. Tension-only or compression-only 

members could not be used except where the dead-load forces in the diagonals were dominant 

and not reversed by a moving live load. Force equilibrium was sufficient to determine the 

member forces for all live-load conditions.

Figure 5.36 Partial elevation of the Sulphite Railroad Bridge Pratt deck truss. HAER NH-36, sheet 3, Arnold M. Kreisel, delineator 2003.

Forms with counters, but not prestressed—This design choice allowed use of tensiononly or compression-only members along an entire span. Only one diagonal was active in 

any one panel, and the truss remained statically determinate. The loose diagonals did not 

contribute to the stiffness of a truss. When a moving live load traversed a span, vibration 

noises might occur as the diagonals were stressed.

Forms with prestressed counters—Appropriate prestressing made all diagonals active for 

the dead load and for all positions of a live load. The system became statically indeterminate, 

and some assumptions had to be 

made before member forces could be 

determined by using equilibrium. All 

diagonals contributed to the stiffness 

of a truss, and some wood dimensional 

changes could occur without a loss of 

stiffness. If the members were ductile, 

the prestressing forces did not decrease 

the maximum live load a truss could 

carry.

The increased use of wrought iron and 

developments in structural analysis through 

the second half of the nineteenth century 

influenced designers’ choices of truss forms. 

In general, stiffness and strength criteria 

Figure 5.37 A 128-foot-long Pratt truss can be found in the

center span of the Honey Run Bridge (ca. 1886), Butte County, 

California. HAER CA-312-5, Jet Lowe, photographer, 2004.
The Development of the American Truss 145

could easily be satisfied with all-metal, statically determinate forms. By the end of the 1870s, 

structural analysis and the design of statically determinate forms became basic engineering skills, 

codified in books and taught at all engineering schools. Since manual statically indeterminate 

analysis was still not practical, assumptions had to be made to determine member forces in 

statically indeterminate trusses. Many engineers saw these assumptions as undesirable, creating 

“ambiguities in stresses.” Moreover, the understanding of structural behavior and structural analysis 

had not developed to the point that prestressing forces could be predicted and controlled by design 

engineers. Engineers were suspicious of contractor-controlled prestressing operations. For these 

reasons, designers increasingly chose statically determinate forms. However, since buckling was 

not a problem in tension-only diagonals, it was most efficient to use this type in all-metal trusses. 

Consequently, until the early twentieth century, designs using non-prestressed, tension-only main 

and counter diagonals remained in wide use in panels near the center of a span where a moving 

live load could cause a force reversal. The counters in the Sulphite Railroad Bridge, built in 1896 

and studied by HAER in 2002, exemplify this view (figure 5.36).68

The Smith Truss

Robert Smith patented a timber truss in 1867 and started a company to build covered bridges using it. 

In 1869, he obtained a second patent, this time for bridge lateral-bracing systems. That year he built 

seventy-five bridges and moved the Smith Bridge Company from Miami County to Toledo, Ohio, 

a Great Lakes port and railroad hub. There he built a factory for the industrial manufacture of 

covered bridges. During the next two decades, the Smith Bridge Company prefabricated hundreds 

of bridges annually for shipment to locations throughout Ohio, Indiana, and Pennsylvania, where 

they were erected by the company’s own crews or by others.69

Some of the company’s success was due to the efficiency of Smith’s truss design, both in the amount 

Figure 5.38 The factory of the Smith Bridge Company in Toledo, Ohio, where workers prefabricated hundreds of timber bridges 

annually for shipment to sites across Ohio, Indiana, and Pennsylvania from 1869 to the 1880s. Courtesy of Miriam Wood Collection.
146 Covered Bridges and the Birth of American Engineering

of materials it required and the amount of labor needed to fabricate it. Smith’s trusses were essentially 

multiple-kingpost trusses whose web tension members (the vertical posts) had been tilted. Tilting 

the tension diagonals roughly doubled the panel length, so Smith’s trusses required only about half 

as many panels as a multiple-kingpost bridge of the same length. The net effect was a reduction in 

the amount of timber used in the truss web. Smith trusses also required fewer notches (and thus 

less fabrication labor) than multiple-kingpost trusses. This was partly because there were fewer 

panels (although not true for Smith “double” or “triple” trusses, described below). Moreover, the 

posts on a vertical-kingpost truss had to be notched to create bearing surfaces for the compression 

diagonals, but on a Smith truss, where the tension and compression diagonals met at nearly a right 

angle, the latter could simply be butted against the former. This eliminated two notches per panel.

Smith introduced industrial techniques to reduce his labor costs. He planed his timbers to precise 

dimensions, which simplified making web-member joints and chord splices. This also allowed 

him to standardize the dimensions of some truss elements (such as fish plates, shear blocks, and 

metal castings) and mass produce them. His trusses were simple to lay out on a factory floor 

with few measurements. The use of scribed marks made the precise cutting of timber joints easy, 

even though truss diagonals were typically at odd angles. (At the Cataract Bridge in Indiana, for 

example, tension diagonals are at 56.4 degrees to the chords, and the compression diagonals are 

mostly at 50.8 degrees.) In short, Smith’s designs incorporated characteristics of nineteenth-century 

industrialization: efficient use of materials, increased labor productivity, and mass production 

techniques that reduced the skill required of that labor.70

The company’s success was also partly due to the industrial machinery Smith invented and installed 

in his factory, including “a gaining-machine [to cut notches in timbers] which does the work of 15 

men,” “a process for making a steel eye-bar [for which he received a patent in 1886],” and “a rotary 

saw, for making the joints of bridge-chords; and a multiple punch, by which six pieces of iron can 

be punched at one operation.”71

The company not only built Smith trusses, it also built covered bridges using Howe and other 

truss types when its customers wanted them. Smith developed a composite truss, much like his 

patented all-timber truss but with iron rods for the tension diagonals, for use in railroad bridges. 

As early as 1870, the company began building all-metal bridges, and it became known for swing 

and draw bridges, too. By 1890, when Smith sold the company, it had stopped making wooden 

bridges altogether.72 Renamed the Toledo Bridge Company, the firm continued in business until 

J. P. Morgan purchased it in 1901. Morgan combined it with twenty-four other bridge companies 

to create the American Bridge Company, which survives today.

The Smith truss was made entirely of wood, with all its web members, except the vertical posts 

at the ends, arranged diagonally. Tension timbers, which splayed outwards towards the ends of 

the bridge, alternated with compression timbers that tilted inwards. This arrangement made the 

Smith truss similar to the Warren truss, a design patented for use in iron bridges. In a Warren 

truss, however, adjacent diagonals met at the truss’s chord, where both were joined to the chord 

with an iron pin. Such a three-piece joint could not be built with heavy timbers. In a Smith truss, 

only web tension members were joined to the chords; web compression timbers were butted into 
The Development of the American Truss 147

Figure 5.39 “R.W. Smith’s Patent Truss Bridge, Tippecanoe City, Miami Co., Ohio,” by Strobridge and Company lithographers,

Cincinnati, ca. 1868. Courtesy of Library of Congress, Prints and Photographs Division, Washington, D.C.

the tension ones just inside the chords.

An important facet of Smith’s 1867 patent was that it allowed for two, three, or more sets of web 

members in the truss, “depending on the strength required.”73 In what the patent called a “single” truss, 

all the web members lay in a single vertical plane, with the tension members sandwiched between and 

notched into paired chord timbers, as in a multiple-kingpost or Burr-arch truss. Smith’s patent, however, 

allowed for the addition of a third piece to the chords to sandwich a second set of web members (a 

“double truss”) or four-piece chords to sandwich three sets of web members (a “triple truss”), and so 

on. An advertising lithograph for Smith’s bridges from about 1868 clearly illustrates this idea. It shows 

three bridges: a short, single truss lightly loaded by a horse and rider, a longer double truss carrying 

a horse-drawn wagon, and a triple truss carrying a train (figure 5.39). The concept of using multiple 

planes of web members resembles, and was perhaps inspired by, Ithiel Town’s second (1835) patent.

A Smith single truss looked like a series of inverted V’s between the chords, with ends like a 

multiple-kingpost truss (where a compression diagonal met a vertical end post at the lower chord). 

Most of the weight of the bridge and the traffic on it was carried by the diagonal into the abutment 
148 Covered Bridges and the Birth of American Engineering

below. The end post carried little vertical load, but it absorbed the diagonals’ outward thrust and 

transferred it into the lower chord through the notched joint between them. 

Three Smith single-truss bridges are known to survive. The Feedwire Road Bridge, a 42-foot span 

built in 1870 and the Jasper Road or “Mud Lick” Bridge, a 71-foot span from 1877, were both 

moved from their original Greene County, Ohio, 

locations and are now in Montgomery County. 

Both also have timber arches bolted to the trusses 

like on a Burr-arch truss, although these arches 

are thought not to be original. A third structure, 

the Salt Creek Bridge, an 83-foot span built 

in 1876 in Muskingum County, Ohio (figure 

5.40), has no documented direct connection 

with Smith and lacks Smith’s typical inclined 

end compression brace.

Figure 5.40 The 83-foot-long Salt Creek Bridge (1876) uses a 

single-web Smith truss with all inclined posts and braces in a 

single plane. HAER OH-127-9, Jet Lowe, photographer, 2004.

A Smith double truss had a second set of web 

members, offset lengthwise from the first. The 

two sets thus formed a series of X’s along the 

length of the truss (figure 5.41). Offsetting the 

two sets had structural advantages but presented 

a problem at the ends of the bridge. There, the 

second set terminated, not with a compression 

diagonal carrying loads into the abutment, but 

with a tension diagonal notched to the upper 

chord. Smith added additional, steeply inclined 

compression timbers to meet these tension 

members and carry their vertical loads to the 

abutment (figure 5.41). Due to their acute angle of 

intersection, both the “extra” brace and the tension 

Figure 5.41 Kidd’s Mill Bridge (1868) is a 122-foot-long Smith

“double truss” (Wilson type 2). Note the steeply inclined 

extra brace at the end panel, with a lightning bolt shaped 

notch. HAER PA-622-5, Jet Lowe, photographer, 2006.

Figure 5.42 Cataract Bridge (1876) is a 140-foot Smith “doubletruss” (Wilson type 3). The truss, the portal bracing, and the lateral

bracing between the upper chords were all patented by Robert

Smith. Note how both tension and compression diagonals are 

notched into the chords at midspan. HAER IN-104-6, James 

Rosenthal, photographer, 2004.
The Development of the American Truss 149

diagonal were notched to provide an end bearing surface for their butt joint. This extra compression 

member, and the lightning-bolt shape of the notch at its end, were distinctive features of Smith trusses. 

About a dozen Smith double trusses survive, with spans between about 50 and 150 feet.

For longer spans Smith used triple trusses with three sets of web members and four-piece chords. 

The early Smith Bridge Company advertisement in figure 5.39 shows a triple truss where each of the 

three webs is offset from the others, and each diagonal therefore crosses two others. If any bridges 

were built this way, none remain. In all eight surviving Smith “triples,” which span between 146 

and 180 feet, the third set of web members is a duplicate of the first, with the second, middle, set 

offset as in a double truss (figure 5.43). Consequently, an elevation view of a Smith triple truss 

appears as a series of X’s, just as a Smith double does.

Figure 5.43 The Powder Works Bridge, built in 1872 by 

the Pacific Bridge Company, is a 180-foot Smith “triple 

truss” (Wilson type 4). One set of diagonals is sandwiched between and offset from two other sets of web 

members, connecting to four-piece chords. The image 

also shows the extra, inclined compression brace on 

the end panel, common to most Smith trusses (a block 

of wood obscures the notched joint). Note Smith-type 

castings fitted over notched joints in upper lateral 

braces. HAER CA-313-8, Jet Lowe, photographer, 2004.

Robert Smith’s covered bridges were also distinguished by the use of the bracing elements contained 

in his 1869 patent, although other builders using Smith’s truss did not always employ them. Smith’s 

knee braces were used to keep the main trusses from leaning to either side. Conventional wooden 

knees at the time extended diagonally from a truss post to a cross beam between the upper chords. 

They were typically used in pairs, one on each side of the bridge, at intervals throughout its length. 

Smith’s knee braces extended beyond the cross beam until they met just under the roof peak, 

and were joined to each other as well as to the cross beam and end posts. This was stronger than 

conventional knees would have been, but Smith never seems to have devised a means of attaching 

his knees to diagonal truss members, so his bracing was found only on the vertical posts at each 

end of the bridge. An example can be seen at the far end of the bridge in figure 5.42.

Smith’s 1869 patent also covered his lateral bracing between lower chords under the bridge’s 

floor and between upper chords under the bridge’s roof. The system commonly used in Smith’s 

time included iron rods in tension between the chords at intervals along the length of the bridge 

and, between adjacent rods, timbers crossed in an X, similar to a Howe truss in a horizontal 

plane. The timber ends in adjacent X’s met, but did not cross, at the chords; they could work 

in compression but not tension. In Smith’s system, the ends of these timbers crossed just before 

they reached the chords and were notched together, as seen in figures 5.42 and 5.43. Then, by 

means of an iron casting that fit over the notched joint, the timbers were bolted to the chord. 
150 Covered Bridges and the Birth of American Engineering

This connection enabled the timbers to resist tension as well as compression, eliminating the need 

for iron rods between the chords.

Over time, Smith altered the way he arranged the timbers near midspan on his trusses, although 

he never patented the changes. His first patent drawings in 1867 show a double truss in which, 

near midspan, each web set has a vertical tension member, with compression diagonals butting into 

notches on both sides of it below the upper chord. This vertical is just like the midspan post on a 

multiple-kingpost truss (figure 5.44a). No extant bridges use this arrangement.

Soon Smith eliminated the tension post and compression braces at midspan. His 1869 patent 

drawings show, instead, two tension diagonals (part of the middle web set of a triple truss) extending 

from midspan on the lower chord outwards in each direction to the upper chord (figure 5.44b). There 

are no corresponding midspan compression diagonals in the other web sets. Only the two oldest 

remaining Smith-truss bridges were built like this: the 1868 Kidd’s Mill Bridge in Mercer County, 

Pennsylvania, and the 1870 Brushy Fork Bridge in Jackson County, Ohio. Similar arrangements 

are shown on all three bridges in his ca. 1868 advertisement (figure 5.39).

Figure 5.44a: Smith truss, from his 1867 patent (Wilson type 1)

Figure 5.44b: Smith truss, from his 1869 patent (Wilson type 2)

Figure 5.44c: Smith truss as built after 1870 (Wilson type 3)

Figure 5.44 Development of Smith’s midspan web member arrangement, drawn by Matthew Reckard.
The Development of the American Truss 151

In the early 1870s, Smith began to include compression diagonals at midspan in the second and, 

if present, third web sets. Under some loading conditions these midspan truss diagonals could 

experience “stress reversal,” i.e. be subjected to tension rather than compression. Smith therefore 

notched them into the chords rather than butt-jointing them to adjoining diagonals (figure 5.44c). 

Raymond Wilson, in a paper published in 1967, classified Smith trusses into four types.74 His type 

1 had the midspan web-member arrangement shown in the first patent drawing; his type 2 had 

the one shown in the 1869 patent. Wilson’s type 3 is the Smith double truss in the post-1870 style. 

Wilson’s type 4 truss was not a chronological development, but rather a Smith triple truss in the 

post-1870 style. It is not clear if Wilson’s type 2 included double trusses, triples, or both, and Smith 

single trusses were not included in his classification system. Despite these limitations, Wilson’s 

taxonomy has commonly been used ever since its publication. 

Structural Behavior of Smith Trusses

The Smith truss proved to be a robust and efficient form of timber truss, but, within a couple of 

decades of its introduction, it, like all timber bridge forms, was largely superseded by metal truss types.

As Smith’s career ended and his company began building large steel movable bridges, he would 

have been using the period’s most advanced structural analysis methods. What design method he 

used for bridge trusses earlier in his career (during the late 1860s and 1870s) is unknown. Analytic 

methods for indeterminate structures like the Smith truss were not available. Smith could have 

approximated his truss and analyzed it as a determinate structure, as a Warren truss.

A 2012 study for the Historic American Engineering Record examined two Smith truss bridges: 

Kidd’s Mill Bridge, built in 1868 in Mercer County, Pennsylvania, and Rinard Bridge, built in 

1876 in Washington County, Ohio.75 The study, by Professor Stephen Buonopane and students 

at Bucknell University, used computerized finite element model (FEM) analysis for both bridges’ 

trusses as originally built. (Post-construction damage and deterioration were not part of the study.) 

The study considered dead load and two live load cases for each bridge. The live load that produced 

higher forces in nearly all members was a linear load of about 550 pounds per foot along the length 

of each truss lower chord, corresponding to a uniform 65 pounds per square foot load on the deck. 

The study results indicated that the Kidd’s Mill trusses, built following Smith’s early form without 

compression diagonals in their central panels, developed substantial bending stresses in the lower 

chords near midspan, while the later Rinard Bridge trusses did not. It seems likely that Smith noted 

this weakness in his early designs and added compression diagonals to correct it.

The study further indicated that under combined dead and live loads, the lower chords of the Kidd’s 

Mill trusses were stressed to almost 100 percent of their calculated allowable capacity, while the 

upper chords, and all the chords on Rinard Bridge, were stressed to considerably less than their 

capacities. The study, however, overestimated the chords’ capacities. The lower chords’ capacity was 

calculated based on the timbers’ full size (gross cross-sectional area) rather than the reduced size 

at their notches (net section), while the allowable compressive stress for the upper chords was not 

reduced to account for buckling considerations. It appeared that, if such adjustments were made, 

the combined loads would stress the upper chords of both bridges, along with the lower chord of 
152 Covered Bridges and the Birth of American Engineering

the Rinard Bridge, to between 90 and 100 percent of capacity, while the lower chord of Kidd’s 

Mill Bridge would be overstressed. This result, that the allowable live load on the bridge chords was 

approximately 550 pounds per foot, suggests that Smith may have been designing his trusses for a 

live load of 1,000 pounds per foot (500 per truss), a typical design value for the period.

The forces in the notched joint between a tension diagonal and the lower chord at one location on 

the Kidd’s Mill trusses were also considered in detail in the study. Several possible failure modes 

were examined, with the critical one found to be shearing of the tension diagonal’s “shoulders” 

beyond the notch. The study indicated the shear force here under dead load alone (6 kips) exceeded 

its calculated allowable capacity (5.76 kips) and that under combined dead and live load, the shear 

force was almost four times the member’s allowable capacity. It appeared, however, that these 

shearing forces may have been greatly overestimated due to methodological issues in the analysis. 

Nevertheless, the conclusion that notched tension joints were one of the weaker details in Smith 

trusses was correct. Buonopane found that the ends of several tension diagonals at Kidd’s Mill had 

either failed in shear and been repaired or had been preemptively strengthened. The 2004–2005 

rehabilitation of Cataract Bridge, an 1876 Smith double truss in Owen County, Indiana, required 

repair of shear failures in the ends of two tension diagonals and in twelve lower chord splices (either 

in the chord timbers or the connecting fish plates). It should be noted, however, that problems with 

timber tension joints were not unique to Smith’s design but were endemic to timber trusses in general.

Observations

The concept of “trussing,” or connecting members in triangulated networks to form a structure, is 

ancient. But it can be fairly said that the American contribution to the practice of using trusses as 

bridges is of international cultural importance. American truss bridges were widely admired and 

copied in Europe in the nineteenth century. Only the most important forms are described here; 

there are many others, representing variations among regions and builders. The variety of truss 

bridges testifies to great ingenuity and construction and engineering skill. Not only were truss 

bridges functional, but the best examples also had great aesthetic appeal. 

Material technology affected truss designs. At the beginning of the nineteenth century, wood was 

the only widely available, economic material. Wood is a versatile, strong material, but it shrinks 

and swells as its moisture content changes and it has time-dependent strain responses to applied 

stress. It is difficult to design efficient connections that can transfer tension forces between wood 

members, and traditional wood joinery was often unsuitable for the force demands of truss bridges. 

The success of Town’s lattice design was largely a consequence of its simple joinery. Simplified 

joinery was also a key feature of Long’s truss designs, which utilized counters and prestressing to 

minimize tension connections. The prestressing process was simplified in the 1840s, when wroughtiron rods were introduced in truss bridges by Howe and Pratt. Cast iron was widely known to be 

relatively weak in tension and was used principally for nodal castings until the 1870s when riveted 

connections were introduced.

The need for reliable truss bridges spurred the development of structural engineering science, which 

in turn led to improved understanding of truss behavior and improved engineering design methods. 

Based on the theoretical developments of Navier, engineering analysis was first applied to the design 
The Development of the American Truss 153

of truss bridges in the 1830s by engineer S. H. Long. By the 1870s, engineers had an essentially 

complete understanding of the structural behavior of statically determinate trusses. Because of this, 

statically determinate forms of the Howe and Pratt trusses became dominant, and more complex 

forms, such as the Burr arch-truss and prestressed forms, fell into disuse. 

Truss forms developed in response to changing transportation needs. There is a direct lineage 

between the small wooden trusses first built to carry people, wagons, and livestock over modest 

spans and the massive all-steel trusses built in the late nineteenth century to carry extremely heavy 

trains over great spans. As the origin of this lineage, American covered wooden truss bridges have 

a special significance in our cultural history.
154 Covered Bridges and the Birth of American Engineering

Endnotes

1 Theodore Cooper, “American Railroad Bridges,” Transactions of the American Society of Civil Engineers

21 (July–December 1889): 1–52; Robert Fletcher and J. P. Snow, “A History of the Development of 

Wooden Bridges,” Paper No. 1864, Transactions of the American Society of Civil Engineers 99 (1934): 

314–54; Richard Sanders Allen, “America’s Covered Bridges,” Consulting Engineer (April 1957): 

92–100. Quote from Richard Sanders Allen, Covered Bridges of the Northeast (Brattleboro, Vt.: Stephen 

Greene Press, 1957), 12.

2 Dennis Hart Mahan, An Elementary Course of Civil Engineering for the Use of the Cadets of the United 

States Military Academy (New York: Wiley and Halsted, 1857), 175; Fletcher and Snow, “History of 

the Development of Wooden Bridges,” 325; Andrea Palladio, Four Books of Architecture (reprint, New 

York: Dover Publications, Inc., 1965), third book, chapter 9. 

 3 Allen, “America’s Covered Bridges,” 11; Lola Bennett, “From Craft to Science: American Timber 

Bridges, 1790–1840,” APT Bulletin 35, no. 4 (2004): 13–19; Squire Whipple, A Work on Bridge 

Building Consisting of Two Essays, the One Elementary and General, the Other Giving Original Plans 

and Details for Iron and Wooden Bridges (Utica, N.Y.: H. H. Curtiss, Printer, 1847), 6.

 4 Mahan, Elementary Course of Civil Engineering, 241–42.

 5 Cooper, “American Railroad Bridges,” 8–9; “Old Highway Bridge at Waterford New York,” 

Engineering News (June 1, 1889), 496–97; Fletcher and Snow, “History of the Development of Wooden 

Bridges,” 331; Llewellyn Edwards, A Record of History and Evolution of Early American Bridges (Orono, 

Maine: University Press, 1959), 49–52; Thomas Pope, A Treatise on Bridge Architecture (New York: 

A. Niven, 1811), 129–39; Herman Haupt, The General Theory of Bridge Construction (New York: D. 

Appleton and Co., 1851), 242–43.

 6 Hubertis M. Cummings, “Theodore Burr and His Bridges across the Susquehanna,” Pennsylvania 

History 23, no. 4 (October 1956): 476–86.

 7 Haupt, General Theory of Bridge Construction, 175.

 8 Emory L. Kemp and J. Hall, “Case Study of Burr Truss Covered Bridge,” Engineering Issues: Journal 

of Professional Activities 101, no. 3 (1975): 391–412; Rachel Sangree, “Gilpin’s Falls Covered Bridge,” 

HAER No. MD-174, 2012.

 9 Edwards, Record of History and Evolution of Early American Bridges, 51. The existing patent consists of 

a drawing only.

 10 Haupt, General Theory of Bridge Construction, 174.

 11 “Jackson Covered Bridge,” HAER No. IN-48; “Kennedy Bridge,” HABS No. IN-24; “Forsythe 

Bridge,” HAER No. IN-106; George E. Gould, Indiana Covered Bridges Thru the Years (Indianapolis: 

Indiana Covered Bridge Society, 1977), 11–16.

 12 Theodore Burr to Reuben Field, February 26, 1815, quoted in “Some Early County Bridges,” Historical 

Papers and Addresses of the Lancaster County Historical Society 11, no. 4 (April 5, 1907), 133.

 13 David Billington, Robert Maillart’s Bridges: The Art of Engineering (Princeton, N.J.: Princeton 

University, 1979), 93.

 14 Roger H. Newton, Town & Davis, Architects: Pioneers in American Revivalist Architecture, 1812–1870

(New York: Columbia University Press, 1942), 44, 73.
The Development of the American Truss 155

 15 Ithiel Town, A Description of Ithiel Town’s Improvement in the Principle, Construction and Practical 

Execution of Bridges (New York, 1839), 6.

 16 John L. Sanders, “Biography of Ithiel Town,” 2009, North Carolina Architects & Builders: A 

Biographical Dictionary, http://ncarchitects.lib.ncsu.edu/people/P000032.

17 Ithiel Town, “Bridge,” U.S. Patent No. 3,169X, January 28, 1820.

 18 Edwards, Record of History and Evolution of Early American Bridges, 56–59; Dylan Lamar and Ben 

Schafer, “Structural Analysis of Historic Covered Wooden Bridges,” Journal of Bridge Engineering 

9, no. 6 (December 2004): 623–33; Lewis M. Prevost, “Description of Howe’s Patent Truss Bridge,” 

Journal of the Franklin Institute 3, no. 5 (May 1842): 289–92.

 19 Carl Culmann, “Der Bau der hölzernen Brücken in den Vereingten Staaten von Nordamerika,” 

Allgemeine Bauzeitung 16 (1851): 69–129.

 20 Cooper, “American Railroad Bridges,” 11.

21 Fletcher and Snow, “History of the Development of Wooden Bridges,” 333; J. P. Snow, “Wooden 

Bridge Construction on the Boston and Maine Railroad,” Journal of the Association of Engineering 

Societies (July 1895), 500–506.

 22 Town, Description of Ithiel Town’s Improvement, 4.

 23 Snow, “Wooden Bridge Construction,” 500–506; David Stevenson, Sketch of the Civil Engineering of 

North America (London: J. Weale, 1838), 234. 

 24 Haupt, General Theory of Bridge Construction, 151.

 25 Lamar and Schafer, “Structural Analysis of Historic Covered Wooden Bridges,” 632.

 26 Allen, Covered Bridges of the Northeast, 15; Edwards, Record of History and Evolution of Early 

American Bridges, 56; “Bunker Hill Bridge,” HAER No. NC-46; Dick Roy, “Old Pompy,” http://www.

vermontbridges.com/cbmail.bag2.htm; “Cornish-Windsor Bridge,” HAER No. NH-8; R. T. Dana, The 

Bridge at Windsor, Vt.. and Its Economic Implications (New York: Condex Book Co., 1926), 33–61; 

David Fischetti, Structural Investigation of Historic Buildings (New Jersey: John Wiley & Sons, Inc., 

2009), 214–18.

 27 George Smart’s bridge is referred to as an “iron bridge” in G. Drysdale Dempsey, Tubular and Other 

Iron Girder Bridges (London: John Weale, 1850), 33; a “mathematical chain bridge” in Olinthus 

Gregory, Mathematics for Practical Men (London: Baldwin, Cradock, & Joy, 1825), 233; and a “chain 

bridge” in David Guise, “Development of the American Metal Lattice Truss Bridge and the Hilton 

Truss,” Structure Magazine (August 2011), 24–26.

 28 “Sir John McNeill,” A Dictionary of Contemporary Biography (London & Glasgow: Richard Griffon 

and Company, 1861), 262; Dempsey, Tubular and Other Iron Girder Bridges, 36; Sir John Rennie, 

Address of Sir John Rennie, President, to the Annual General Meeting, January 20, 1846 (London: 

Institution of Civil Engineers, 1846), 18. Quote from R. W. Liscombe, “A ‘New Era in My Life’: Ithiel 

Town Abroad,” Journal of the Society of Architectural Historians 50, no. 1 (March 1999): 5.

 29 Olinthus Gregory, Mathematics for Practical Men (London: Baldwin, Cradock, & Joy, 1825), 239; 

Town, Description of Ithiel Town’s Improvement, 4, 11. 

 30 Whipple, Work on Bridge Building, 11–31.

Endnotes
156 Covered Bridges and the Birth of American Engineering

 31 The weight of half of the bridge span is 187,500 pounds, and the total brace force considers the fact 

that there are four truss frames.

 32 William Humber, Practical Treatise on Cast and Wrought Iron Bridges and Girders (London: E. and F. 

N. Spon, 1857), 14, 92–100.

 33 Stephen H. Long, Rail Road Manual, or, a Brief Exposition of Principles and Deductions Applicable 

in Tracing the Route of a Rail Road (Baltimore: William Wooddy, 1829). Long’s patents include no. 

5,862X, March 6, 1830; no. 7,351X, December 28, 1832; no. 7,372X, January 17, 1833; no. 7,570X, 

January 17, 1833; no. 9,340X, January 23, 1836; and nos. 1,397 and 1,398, both November 7, 1839.

 34 The specifications for Long’s 1830 patent appear in Journal of the Franklin Institute 5, no 4 (April 

1830): 234. A Long truss built in 1831 at Mattawamkeag, Maine, by Capt. Charles Thomas on the 

Aroostook Military Road apparently used the upper arch braces, as suggested by an exterior photograph 

showing an odd cross gable roof.

 35 Stephen H. Long, Description of the Jackson Bridge, Together with Directions to Builders of Wooden or 

Frame Bridges (Baltimore: Sands & Neilson, 1830), 7.

 36 Stephen H. Long, “Remarks on the Jackson Bridge,” Journal of the Franklin Institute 4, no. 2 (August 

1830): 110, 112.

 37 Allen, Covered Bridges of the Northeast; Richard Sanders Allen, Covered Bridges of the Middle Atlantic 

States (Brattleboro, Vt.: Stephen Greene Press, 1959); Stephen H. Long, Description of Col. Long’s 

Bridges Together with a Series of Directions to Bridge Builders (Concord, N.H.: John F. Brown, Printer, 

1836), 43–47.

 38 Stephen H. Long, “Truss Bridge,” U.S. Patent No. 9,340X, January 23, 1836. 

39 Long, Description of Col. Long’s Bridges, 25.

 40 Culmann, “Der Bau der hölzernen Brücken,” 69–129; D. Gasparini and C. Provost, “Contribution 

of Stephen Harriman Long to the Design of Trusses,” Proceedings of the CSCE Centennial Conference, 

Montreal, Canada, May 19–22, 1987, 804–11; D. Gasparini and C. Provost, “Early Nineteenth 

Century Developments in Truss Design,” Construction History 5 (1989): 21–33.

 41 Stephen H. Long, U.S. Patent Nos. 1,397 and 1,398, November 7, 1839; idem, “Specification of a 

patent for a suspension bridge” and “Specifications of a patent for an improved bridge, denominated 

a brace bridge,” Journal of the Franklin Institute 24, no. 5 (November 1839): 325–33; idem, “Colonel 

Long’s Bridges,” Journal of the Franklin Institute, third series, vol. 2, no. 3 (September 1841): 175.

 42 Culmann, “Der Bau der hölzernen Brücken,” 73–74. Dario Gasparini gratefully acknowledges the 

assistance of Dr. Frank Rausche of Cleveland, Ohio, who translated Culmann’s remarks on Long from 

the German.

 43 Dario Gasparini and David Simmons, “American Truss Bridge Connections in the Nineteenth 

Century. I: 1829–1850,” Journal of Performance of Constructed Facilities 11, no. 3 (August 1997): 119–

29; Fletcher and Snow, “History of the Development of Wooden Bridges”; Allen, Covered Bridges of the 

Northeast, 17–18; J. G. James, “The Evolution of Wooden Bridge Trusses to 1850 [part 2],” Journal of 

the Institute of Wood Science 9, no. 4 (December 1982): 176–77.

 44 Marc Seguin, Des Ponts en Fil de Fer, 2nd ed. (Paris: Chez Bachelier, Libraire, 1826); Tom F. 

Peters, Transitions in Engineering: Guillaume Henri Dufour and the Early 19th Century Cable 

Suspension Bridges (Basel, Switzerland: Birkhäuser Verlag, 1987); M. Cotte, “The Tournon-Train 

Suspension Bridge: A Case Study in Technology Transfer and Innovation, 1821–1825,” Proceedings 

Endnotes
The Development of the American Truss 157

of an International Conference on Historic Bridges to Celebrate the 150th Anniversary of the Wheeling 

Suspension Bridge, Wheeling, W.Va., October 21–23, 1999, 47–58.

 45 “Description of the Freyburg Suspension Bridge,” Journal of the Franklin Institute 16, no. 3

 (September 1853), 202.

 46 A. Kahlow, “Johann August Roebling (1806–1869): Early Projects in Context,” Proceedings of the 

John A. Roebling Symposium organized by the New Jersey and Metropolitan Sections of the ASCE, 

Brooklyn, New York, October 27, 2006; C. F. W. Berg, Der Bau der Hängebrücken aus Eisendraht

(Leipzig, 1824); Emory Kemp, “Charles Ellet and the Wheeling Suspension Bridge,” Proceedings of 

an International Conference on Historic Bridges to Celebrate the 150th Anniversary of the Wheeling 

Suspension Bridge, Wheeling, W.Va., October 21–23, 1999, 15–31; Charles Ellet, A Popular Notice 

of Wire Suspension Bridges (Richmond, Va.: P. D. Bernard, 1839); Charles Ellet, Report and Plan 

for a Wire Suspension Bridge, Proposed to be Constructed Across the Mississippi River at Saint Louis

(Philadelphia: W. Stavely & Co. Printers, 1840); Charles Ellet, A Popular Notice of Suspension Bridges, 

with a Brief Description of the Wire Bridge across the Schuylkill at Fairmount (Philadelphia: J. Clark, 

1843), 7, 30; D. Sayenga, “Fairmount Suspension Bridge,” in Baltimore Civil Engineering History, ed. 

Bernard G. Dennis Jr. and Matthew C. Fenton IV (Reston, Va.: American Society of Civil Engineers, 

2005), 265–309.

 47 William Howe, “Truss Frame for Bridges,” U.S. Patent No. 1,685, July 10, 1840.

 48 William Howe, “Truss Bridge,” U.S. Patent No. 1,711, August 3, 1840. A recent study of the Howe 

patent files suggests that the patent examiner recommended separating what had initially been a single 

application from Howe into two separate applications; Dario Gasparini, personal communication with 

D. Sayenga, 2006. 

 49 Berg, Bau der Hängebrücken aus Eisendraht, table II, fig. 10; Seguin, Des Ponts en Fil de Fer, fig. 10; 

Ellet, Report and Plan for a Wire Suspension Bridge, plate 1, fig. 5.

 50 Albert Parry, Whistler’s Father (Indianapolis: Bobbs-Merrill Company, 1937); C. E. Fisher, “Whistler’s 

Railroad: The Western Railroad of Massachusetts,” Railway and Locomotive Historical Society 

Bulletin, 69 (1947); Allen, Covered Bridges of the Northeast, 66; M. Joblin, Cleveland, Past and Present

(Cleveland, Ohio: Fairbanks, Benedict, 1869), 301.

 51 Annual Report of the Directors of the Western Railroad Corporation to the Stockholders (Boston: S. N. 

Dickinson, 1840), 14.

 52 Annual Report of the Directors of the Western Railroad Corporation to the Stockholders, 14.

 53 Joblin, Cleveland, Past and Present, 302; Victor C. Darnell, A Directory of American Bridge-Building 

Companies, 1840–1900 (Washington, D.C.: Society for Industrial Archaeology, 1984).

 54 Prevost, “Description of Howe’s Patent Truss Bridge,” 292; “Notes on Practical Engineering No. 5. 

Bridges,” American Railroad Journal and Mechanics’ Magazine 17 (January 1844): 42–43. The chord 

sizes given on the drawing published in the Journal of the Franklin Institute in 1842 do not agree with 

the chords illustrated on plate 122 of J. Weale’s Theory, Practice, and Architecture of Bridges (London: 

John Weale Architectural Library, 1843). Since G. W. Whistler provided the drawings to Weale, we 

must assume that the sizes provided by the Franklin Institute are incorrect.

 55 Joblin, Cleveland, Past and Present, 300.

 56 William Howe, U.S. Patent No. 4,726, August 28, 1846.

 57 Joblin, Cleveland, Past and Present, 303; E. L. Kemp and R. K. Anderson, “The Reading-Halls Station 

Bridge,” IA 13, no. 1 (1987): 17–40; Gasparini and Simmons, “American Truss Bridge Connections,” 

123; Ohio General Assembly, Joint Committee Concerning the Ashtabula Bridge Disaster, Report of the 

Endnotes
158 Covered Bridges and the Birth of American Engineering

Joint Committee Concerning the Ashtabula Bridge Disaster (Columbus: Nevins & Myers, 1877), 82. 

 58 James, “Evolution of Wooden Bridge Trusses to 1850 [part 2],” 192; John Weale, The Theory, Practice, 

and Architecture of Bridges of Stone, Iron, Timber and Wire (London: 1843), plate 122.

 59 S. Timoshenko, “D. J. Jourawsky and His Contributions to Theory of Structures,” in FederhoferGirkmann-Festschrift (Vienna: F. Deuticke, 1950), 115–23; idem, History of Strength of Materials

(New York: McGraw-Hill, 1953), 141, 186–89; D. Jouravsky, About Bridges of the Howe System (St. 

Petersburg: D. Kesneville, Typographers, 1855–56).

 60 Carl Ghega, Über Nordamerikanischen Brückenbau und berechnung des tragungsvermögens der 

Howe’shchen Brücken (Vienna: Kaulfuss Witwe, Prandel and Compaigne, 1845).

61 Culmann, “Der Bau der hölzernen Brücken,” 74.

 62 Culmann, “Der Bau der hölzernen Brücken,” plate 390; Philip S. C. Caston, Germany’s Remaining 

Historic Wooden Bridges (Neubrandenburg, Germany: Hochschule Neubrandenburg, Fachbereich 

Landschaftsarchitektur, Geoinformatik, Geodäsie und Bauingenieurwesen, 2010), 144–45; Stefan 

M. Holzer, Die König-Ludwig-Brücke Kempten, Historische Wahrzeichen der Ingenieurbaukunst in 

Deutschland 11 (Berlin: Bundesingenieurkammer, 2012).

 63 “Description of Howe’s Bridge, 1853,” Covered Bridge Topics 68 (Winter 2010): 3–7; “Ole Haldorson, 

Oregon Bridge Builder: An Interview,” Covered Bridge Topics 71 (Winter 2013): 3–10.

 64 Francesca da Porto, “Pine Bluff Bridge,” HAER No. IN-103, 2002.

 65 “Thomas Willis Pratt,” Annals of the Massachusetts Charitable Mechanics Association 1795–1892

(Boston: Press of Rockwell and Churchill, 1892), 211–12.

 66 Caleb Pratt and Thomas W. Pratt, “Truss Bridge,” U.S. Patent No. 3,523, April 4, 1844; Gasparini and 

Simmons, “American Truss Bridge Connections,” 126.

 67 Dario Gasparini, J. Bruckner, and Francesca da Porto, “Time-Dependent Behavior of Posttensioned 

Wood Howe Bridges,” Journal of Structural Engineering 132, no. 3 (2006): 418–29.

 68 Megan Reese, “Sulphite Railroad Bridge,” HAER No. NH-36.

 69 Clark Waggoner, ed., History of the City of Toledo and Lucas County (New York: Munsell & Co., 

1888), 786–87; Eldon M. Neff, “Highlights in the Life of Robert W. Smith,” Connecticut River Valley 

Covered Bridge Society 11, no. 4 (Spring 1963); S. Buonopane, S. Ebright, and A. Smith, “The Timber 

Trusses of R. W. Smith, History, Design and Behavior,” Proceedings of the Fourth International Congress 

on Construction History, Paris, July 3–7, 2012, 599–606.

 70 Matthew Reckard, “Smith Trusses: Bringing Covered Bridges into the Industrial Age,” Covered Bridge 

Preservation National Best Practices Conference, University of Vermont, June 2003, www.uvm.edu/

coveredbridges/papers/reckard.html.

 71 Waggoner, History of the City of Toledo, 786.

 72 Waggoner, History of the City of Toledo, 786; Neff, “Highlights in the Life of Robert W. Smith.”

 73 Robert W. Smith, U.S. Patent No. 66,900, July 16, 1867. 

 74 Raymond E. Wilson, “The Story of the Smith Truss,” Covered Bridge Topics 25 (April 1967): 3–5.

 75 Stephen Buonopane, Sarah Ebright and Alex Smith, “Structural Study of Smith Trusses,” HAER No. 

PA-645, 2012.

Endnotes
 

Chapter 6
 

Builders and Practices 


by Joseph D. Conwill 

The covered bridge builder comes 

down to us in folklore as a

legendary figure akin to Paul

Bunyan.1 In reality the builders were a

varied group of people. Despite the fact 

that some were self-educated and few had 

formal engineering training, they did not 

build their bridges by guesswork. Instead, 

covered bridge builders understood

complicated structural principles through

experience gained on the job and by

observation. J. P. Snow, bridge engineer 

with the Boston and Maine Railroad,

noted that “when an intelligent mastercarpenter has had the care for a term of 

years of a line of wooden bridges covering 

any given style of truss, he gradually brings

their parts, when building new ones, to 

almost the exact size called for by scientific

analysis when actual loads are used in calculation.”2 This experiential knowledge was essential because

building timber bridges is not, as is often stated, like building houses or barns. Some of the joinery 

skills may be similar, but the challenge of using timber to span a hundred feet or more of open space 

is quite different from building on a foundation. Although many covered bridge builders did other 

types of construction, particularly where their specialized knowledge of how to span open spaces 

was useful, it is, ultimately, for their covered bridges that these builders are remembered today.3 

Figure 6.1 The Norris Ford Bridge, Rush County, Indiana, was

constructed in 1916. White-bearded builder Emmett L. Kennedy

(1848–1938) is second from the front. Courtesy of National Society for

the Preservation of Covered Bridges. 

The term “builder” may be used in different ways. In the broadest sense, a builder uses tools to make

something. In terms of covered bridges, the builder was really a contractor with the ultimate legal 

responsibility for completing a large construction job. Some builders, such as Theodore Burr or 

Lewis Wernwag, also provided original designs for their bridges—in other words, they functioned 

as engineer/architects. Others used patented designs that they adapted as needed. Builders usually 

Builders and Practices 159
Figure 6.2 Top: 6.2a) Pine Grove Bridge (1884) once illustrated the general pattern of X-braced floor framing found in covered

bridges in Lancaster County, Pennsylvania. Since the decking and stone abutments have been replaced by steel beams and

concrete, these floor details no longer exist. HAER PA-586-2, Jet Lowe, photographer, 2002. Above: 6.2b) On the other hand,

Dreibelbis Station Bridge (1869) retains the three-panel-long latticed style floor framing typical of covered bridges erected in

Berks County, Pennsylvania. HAER PA-587-7, Jet Lowe, photographer, 2002.

160 Covered Bridges and the Birth of American Engineering 
had extensive hands-on experience in construction and closely supervised the layout even if their 

crews did most of the physical labor, but there were exceptions even to this. Lewis Wernwag was 

very skillful at construction, but for some of his later bridges it appears that he only provided plans 

and perhaps never even visited the sites in person. On the other hand, William Henry Gorrill of 

the Pacific Bridge Company is listed as builder for several significant California structures, but it 

is unlikely that he handled tools himself. He was a lawyer by training, and the actual construction 

of his bridges was done by subcontractors or hired crews whose names are largely forgotten.4 

Builders worked for a variety of entities, since covered bridges were financed in a number of ways. 

The large, early covered bridges were generally built for toll-bridge companies, since governments 

typically did not have enough capital for large-scale construction projects in the early nineteenth 

century. Notable exceptions were the bridges on the National Road, whose construction was

federally funded. Later in the nineteenth century, government entities contracted with builders to 

erect covered bridges on smaller crossings on local roads; tolls were not generally charged on these 

crossings. In New England and in New York, town governments were responsible for most of the 

public works within their boundaries. From Pennsylvania on south and west, public works were 

usually a county responsibility, and the elected county commissioners would award bridge contracts

directly. (Naturally, the commissioners had their trusted favorites.) By the twentieth century, the 

county engineer typically made the maintenance decisions. While private contractors built Oregon’s

early covered bridges, county bridge crews erected those built into the mid-twentieth century. The 

state provided suggested plans, but county engineers modified them as they saw fit and designed 

the housings.5 

The structure of the local government, therefore, influenced the design of covered bridges.

Examining Pennsylvania’s Burr-arch truss covered bridges illustrates the impact of having county 

commissioners award bridge contracts, as there are marked differences between counties. Covered 

bridges in Lancaster County exhibit classically framed Burr-arch trusses, including floor beams 

placed at the panel points and lower lateral bracing in the form of an X. Berks County Burr-arch 

trusses have floor beams placed throughout the panel and an unusual latticed style of lower laterals. 

(It is just such local framing details that are lost when floors are replaced with steel beams during 

repairs, or when engineers reconfigure covered bridges to generic designs.) Burr-arch trusses in 

Perry County sometimes use just a single treenail to fix the post at the top-chord joint instead of 

the usual two. Further west, the Burr-arch trusses of Somerset County usually have braces mitered 

into the post-chord joints instead of being placed on the shoulders of the posts.6 In Oregon, Howe 

trusses are typically used, but they vary between counties, since county engineers had the authority 

to modify the basic plans. In Linn County, many of the Howe trusses have open sides and are 

painted white. Lane County also uses Howe trusses, but the sides are boarded nearly to the top.7 

Lincoln County’s covered bridges have flared sides and are painted red, although most of them have

been lost. County styles are less distinct in places like Ohio, where individual builders competed 

against larger companies, such as the Smith Bridge Company or the Hocking Valley Bridge Works, 

which built across a wide area. Uniformity in New England counties is non-existent since there 

were no big bridge companies involved in the region and town governments were responsible for 

transportation structures.

Builders and Practices 161 
Figure 6.3 Top: 6.3a) The sides of the Howe trusses in Linn County, Oregon, as in Short Bridge (1945), were left open. HAER

OR-120-6, Jet Lowe, photographer, 2004. Above: 6.3b) Covered bridges in Lane County, Oregon, like Horse Creek Bridge (1930,

moved 1990), were covered nearly to the top chord. HAER OR-15-2, James Norman, photographer, 1987. 

162 Covered Bridges and the Birth of American Engineering 
Figure 6.4 Sunday River Bridge (1872) in Oxford County, Maine, is a good example of the Paddleford truss, which became the

dominant regional truss in parts of New Hampshire, Maine, and Vermont in the late-nineteenth century. HAER ME-69-11, Jet

Lowe, photographer, 2003. 

Existing bridges were another major design influence on newer bridges. While the written record 

rarely contains the reasons why bridge committees or county commissioners chose one kind of bridge

construction over another, the built environment offers some clues. For example, Col. Stephen H. 

Long had just patented his bridge truss when the Aroostook Military Road (now U.S. Highway 2) 

was constructed through northeastern Maine. Capt. Charles Thomas used the Long truss for his 

1831 bridge at Mattawamkeag in Penobscot County on this road. The Long truss then became, 

because of its familiarity, a dominant building type in central and eastern Maine, but it was not 

common elsewhere in the state.8 Theodore Burr built many bridges in Pennsylvania, where the Burrarch truss is still a dominant form today. However, Solon Chapin used the Town lattice truss for 

an 1835 bridge over the Delaware River at Lumberville, and in adjacent Bucks County this became 

the prevalent type instead of the Burr. Peter Paddleford of Littleton, New Hampshire, designed 

his own bridge truss and set a precedent by using it for several important crossings in the central 

part of his state. Even after Paddleford’s death in 1859, other builders kept using his design, and 

it became a dominant form over a large portion of northern New England from Orleans County, 

Vermont, through Oxford County, Maine.9 

Still more intriguing is the interplay between the Burr and the Wernwag trusses. Both forms involved

an arch combined with a multiple-kingpost truss, and both had several framing variants. In general,

the Burr-arch truss used posts which were vertical or nearly so, and it had a single truss sandwiched 

between a pair of arches. The Wernwag truss usually did the opposite and used a single heavy arch 

built up of several ribs sandwiched between a pair of trusses using flared posts; that is, the posts 

inclined outwards at the top, more so toward the ends of the bridge, being about perpendicular to 

Builders and Practices 163
the arch as they intersected it. There was interplay between the Burr and Wernwag forms. No purely

Wernwag trusses exist today, but there are Burr-arch trusses which use the flared posts. Although the

distribution of this framing variant is not regular, it is found especially along the southern border 

of Pennsylvania where Wernwag himself was once active. His building partners worked further 

west across southern Ohio and Indiana, and Burr-arch trusses with apparent Wernwag influence 

are found in this region and as far afield as northeastern Missouri. 

Figure 6.5 Huffman Mills Bridge (1864) in Perry and Spencer counties, Indiana, is a Burr-arch truss with the flared-post style

used in the Wernwag tradition. Joseph D. Conwill, photographer, 2003. 

The cost of erecting a covered bridge varied not only because of the size of the structure, but also 

because of where and when it was built. The cost of stonework for the abutments could constitute 

half or more of the total expense, but sometimes the abutments from a prior bridge could be used. 

The Schuylkill Permanent Bridge at Philadelphia, the first known covered bridge in the United States,

cost over $275,000 in 1801–1805, which was a fabulous sum of money at the time. The bridge was 

550 feet long, a total of 1,300 feet with the stonework approaches, and it sat in the midst of some 

of this country’s prime real estate. The total cost included the massive foundations and $40,000 for 

the land. As the technology became more common and covered bridges were built in more remote 

locations where land prices were not so expensive, the cost of construction decreased, as shown in 

the accompanying graph. Some very small bridges even went up for $500 or less. It is difficult to 

attribute these modest prices to a single cause, but one explanation may be the competition from 

iron-bridge builders. Another may be the deflationary trend of the late-nineteenth-century economy

in general. Surprisingly low costs continued into the twentieth century in Oregon even as inflation 

rose, probably because first-class timber was abundant and inexpensive there.10

164 Covered Bridges and the Birth of American Engineering 
Comparison of Bridge Construction Costs 

Name of bridge Location Date of 

construction Length Cost Notes 

Bath-Haverhill Bridge New Hampshire 1829 256’ $2,400 

Eldean Bridge Ohio 1860 219’ $4,080.83 Cost included 

foundations 

Dreibelbis Bridge Pennsylvania 1869 172’ $6,000 Cost included 

foundations 

Johnson’s Mill Bridge Ohio 1876 83’ $1,302.22 Cost included 

foundations 

Brown Bridge Vermont 1880 112’ $1,078.37 Cost included 

foundations 

Forsythe Bridge Indiana 1888 186’ $3,800 

Ritner Creek Bridge Oregon 1927 75’ $6,693.78 

The history of timber-bridge design is also characterized by an effort to reduce the use of custom 

joinery. Trusses such as the Burr, Long, and Paddleford required traditional woodworking skills. 

The Town lattice was the first attempt to use standardized pieces of timber, yet it should not be 

assumed that any carpenter was capable of building such a bridge. A high degree of skill was still 

required to lay out a Town lattice truss, especially given the camber that was required. Building 

Figure 6.6 Arnold Graton erected a replacement for the Hall Bridge across Saxtons River in Windham County, Vermont, in 1982. Using 

traditional techniques, Graton Associates developed rough specifications from the original 1867 bridge and then framed it in a nearby 

field using traditional joinery and treenails. A team of oxen hauled the completed structure out across the river, and the bridge opened 

to traffic on September 6, 1982. Jack Peters, photographer, 1982. (See “Hall Bridge,” HAER VT-40 for additional information.) 

Builders and Practices 165 
a Howe truss might seem to require less expertise if the pieces were precut elsewhere, but it, too, 

required special knowledge of such details as the correct spacing of the lower chord joints and the 

sequence of tightening the rods.11 Bridge building was always a skilled job, no matter what truss 

type was used. The only clearly documented cases of covered bridges being built by truly untrained 

labor were the Town lattices of the 1890–1955 period designed by the Department of Colonization 

in Quebec for construction by settlers in new regions.12 These bridges used spikes instead of wooden

treenails at the lattice joints and required no custom cutting.13 

Building a Typical Bridge 

When residents of a New England town decided a new bridge was needed in their neighborhood, they

brought the subject up at the annual town meeting. If voters approved the project, a bridge committee

would be appointed and authorized to deal with a builder. A bridge request might be postponed for 

a year or more depending on finances, since bridge construction was one of a town’s most expensive 

responsibilities. In other parts of the country, residents would petition the county commissioners, or 

a court with executive authority, that would appoint a committee of impartial viewers. If the ruling 

body judged the project worthy, the commissioners would then publish a call for bids. The same builder

might submit several bids for bridges with different truss types or with varying degrees of finish.14 

The builder might arrange for construction of the abutments, but these were often the subject of a 

separate contract. Bridge abutments used a wide variety of materials. New England bridges often 

used dry-laid split stone, sometimes in regular courses but usually in carefully chinked random 

courses.15 Since stone was expensive to transport, local stone was typically used. A few covered 

bridges in Rutland County, Vermont, sat on marble abutments, for example, because the marble 

industry was centered there. Bridge abutments in southeastern Pennsylvania almost always used 

random-coursed, mortared masonry. Ohio and Indiana builders preferred regular courses of cut 

and dressed stone, although concrete was used for a few later bridges. The abutments of covered 

bridges in the South used a variety of materials, including brick in northeastern Mississippi. Oregon’s

twentieth-century covered bridges typically had concrete abutments. Those in Canada often used 

timber cribs. 

In order to construct the bridge superstructure, the builder had to procure the timber, although in 

New England some towns made this purchase. Early in the nineteenth century, the timber might 

be cut on or near the site, such as was done at the 1836 Taftsville, Vermont, bridge. This practice 

extended into the twentieth century in timber-rich Oregon. When timber was cut near the site, there 

was inadequate time for seasoning. Designers such as Lewis Wernwag, Stephen Long, and William 

Howe, consequently, made allowances in their designs for timber shrinkage. When Ephraim Ballard 

built the Kennebec Bridge at Augusta, Maine, in 1827, it was reportedly completed and in service 

just seventy-four days after the timber had been cut. By the latter half of the nineteenth century, 

though, much of the good local timber in the East had been cut, so timber often had to be brought 

in from elsewhere. A few builders such as James Tasker of Sullivan County, New Hampshire, and 

John Davidson of Sullivan County, New York, owned woodlots and sawmills, but more often builders

obtained timber through market distribution channels. Many timber species were used, the choice 

depending on a bridge’s location, and different varieties could even be used within a single bridge if 

called for in the bridge specifications. For example, spruce was commonly used for lattice trusses in 

166 Covered Bridges and the Birth of American Engineering 
 

   

 

New England. Midwestern covered bridges used 

pine or poplar for truss posts and braces. Indiana 

builder J. J. Daniels liked using white oak for his 

bottom chord sticks and various hardwoods for 

floor planks. Builders in New Brunswick used 

hackmatack (a regional term referring to tamarack

or larch) for Howe-truss bearing blocks.16 At the 

end of the nineteenth century, southern longleaf

pine was widely used, due to the depletion of other

species and its ready availability by rail shipment.17 

Figure 6.7 Falsework is in place for the construction of Hendricks

Bridge over McKenzie River, Lane County, Oregon, in 1907.

Courtesy of Bill Cockrell Collection.

Milled lumber was used for most later bridges, but

the length of individual members was limited by 

the size of sawmill carriages.18 The Town lattice 

used shorter lengths, and other trusses often used

chords built up of short lengths. In those bridges 

where long, single sticks were desired, they were

occasionally still hand-hewn even if the remainder

of the bridge used milled lumber.19 The layout 

and cutting of the timbers was done in advance 

at the bridge site, although a few builders such as 

the Kennedys of Indiana or Jacob Brandt of Ohio

did this work in central work yards near their 

homes.20 Smith-truss parts were nearly always

prefabricated at the factory, as were some Howe 

trusses, especially those for railroad use. Once

the stonework for the abutments was done, the 

truss framing could take as little as a few weeks 

to erect for a short bridge or up to several months 

for a long one. 

Figure 6.8 Construction of the Hendricks Bridge in 1907 began


by laying out the bottom chords on the falsework.


Courtesy of Bill Cockrell Collection.
 

Figure 6.9 With its Howe trusses fully erected, the Hendricks

Bridge was nearing completion when this photograph

was taken in 1907. Courtesy of Bill Cockrell Collection. 

The tools used to build a covered bridge varied 

with the type of truss. Traditionally framed

designs such as the Paddleford, the Burr, or

even the Howe as built in back-country Oregon 

required “axes, adzes, shovels, picks, hand saws, 

splitting froes, sledges, splitting mauls, dollies 

. . . augers, jacks, peavies, hammers, nails, ropes,

hand winches, [and] drift pins” according to

a 1902 account from Oregon.21 Town-lattice

construction required a hand-cranked boring

machine to ensure that the holes were precisely 

perpendicular to the planks.22 After the timbers

were cut, the falsework (scaffolding) was placed 

Builders and Practices 167
in the river, and the truss was assembled piece by piece atop the falsework. It was not uncommon 

to open a bridge to traffic before the roofing and siding had been completed. The work was subject 

to final inspection by the bridge committee or the commissioners, and, if they found deficiencies 

in construction, they could reduce the builder’s pay accordingly. Sometimes builders performed a 

follow-up visit a few years later to make adjustments for shrinkage of the timber.23 

In contrast, covered railroad-bridge construction involved the mobilization of vast resources over 

an extended territory and, consequently, was handled in a more centralized manner. Some railroads

had their own engineers for design, and others even used their own building departments, resulting 

in similarly designed bridges across the railroad. The vast expanses to be traveled by railroads in 

the Midwest and West required a high degree of organization, and large outside contracting firms 

specializing in railroad work were generally hired to do the building. Stone and Boomer of Chicago 

was one of the largest and best-known railroad-bridge contractors, working with many lines

throughout the Midwest. Since partner Andros B. Stone was brother to the wife of truss-inventor 

William Howe, and his older brother, Amasa Stone Jr., had been involved in the actual development

of the Howe truss, their bridges primarily utilized the Howe truss. In Oregon, the firm of Hoffman 

and Bates handled a great deal of railroad construction and pioneered a radical housing style with 

rakish back-slanted portals and a hip roof; unfortunately, no examples of this survive.24 Because of 

the rapid increase in size and weight of rolling stock throughout the nineteenth and early twentieth 

centuries, railroad bridges usually had short service lives, sometimes as little as fifteen years. If a 

main-line bridge was still sound when replaced, it was not uncommon to move it elsewhere on a 

branch line where service demands were lower.25 

Covered Bridge Builders 

The names and stories of many covered bridge builders have been lost. Most used the designs of 

others, such as Theodore Burr, Ithiel Town, William Howe, and Robert W. Smith, sometimes 

adding their own distinctive variations. A comprehensive listing of known covered bridge builders 

would require a book in itself, but some of the best known are included here to illustrate their 

widely differing backgrounds and the various ways in which covered bridge construction took place. 

Figure 6.10 Barrackville Covered Bridge (1853), a Burr-arch truss built by Lemuel

Chenoweth on the Fairmont and Wheeling Turnpike in Marion County, West Virginia.

HAER WV-8-25, Jet Lowe, photographer, 2002. 

Lemuel Chenoweth was born in 

1811 near Beverly, Virginia (now 

West Virginia). The mellifluous 

family name is of Cornish origin.

Although Chenoweth was listed

in census records as “bridge

builder,” he also undertook many

other construction projects,

including building houses, a

church, wagons, and furniture.

Chenoweth was also an inventor,

working on sawmill equipment

and a machine to lay the Atlantic

telegraph cable, although the

168 Covered Bridges and the Birth of American Engineering 
 

 

latter was never put to use. Two of his covered bridges survive; both are in West Virginia, one in 

Philippi and the other in Barrackville. Because these bridges saw heavy use, they have been the 

subject of major restoration work. Steel beams have carried the live loads at Philippi since the 1930s,

and the bridge was damaged by a serious fire in 1989. Chenoweth preferred the Burr-arch truss, 

and he placed the tie beams on the post tops high over his two-part top chords.26 His fame rests 

on his personal versatility as an inventor and on the fact that his covered bridge at Philippi is the 

last in service on a U.S. numbered highway.27 

Joseph John Daniels (commonly known as J. J. Daniels) was one of the most skillful and prolific 

covered bridge builders in western Indiana. Born in 1826 in Marietta, Ohio, he was the son of 

Stephen Daniels, an agent for the Stephen H. Long bridge interests. J. J. Daniels is said to have 

had limited exposure to formal education, but he was apparently educated at home by his parents, 

read very widely on a variety of subjects, and knew ancient Greek and Latin. Before the age of 

twenty-one, he was building bridges and moved his practice to western Indiana in the 1850s. Bridge

construction was apparently his primary activity, and he built over fifty of them, both for highway 

and for railroad use. Daniels built his last covered bridge in 1904 around the age of seventy-eight; 

he lived to ninety. J. A. Britton and his sons built bridges until 1920 that are somewhat similar in 

detail to Daniels’s bridges, and both Daniels and Britton account for the majority of covered bridges

in Parke County, Indiana, which is a great center of covered bridges.28 

Daniels used a variety of 

trusses, but he preferred

the Burr, to which he introduced some distinctive

modifications. In most

Burr-arch trusses, the

arches are notched into

the trusses. In Daniels’s

bridges, they splay outwards and pass outside

of the bottom chords

of the truss instead of

being notched in. He

did not tighten the bolts 

connecting the arches

to the truss until after

the falsework had been

removed, indicating that 

he intended the arches

mainly to carry the live

load on the bridge.29 In some of his multi-span bridges, he built continuous top chords over the 

piers. This increased load capacity of the bridge overall and was a sophisticated engineering feature. 

His bridges are also characterized by the use of iron rods rather than wooden tie beams in the upper 

lateral systems, which is unusual in Burr-arch trusses.30 

Figure 6.11 A view underneath West Union Bridge (1876) in Parke County, Indiana, shows

how J. J. Daniels splayed his arches around the bottom chords of the trusses. HAER IN-105-9, 

James Rosenthal, photographer, 2004. 

Builders and Practices 169 
Figure 6.12 Powder Works Bridge (1872) in Santa Cruz Couty, California, is an 

excellent example of the early work of the Pacific Bridge Company and of the Smith 

type 4 triple-web truss. HAER CA-313-10, Jet Lowe, photographer, 2004. 

William Henry Gorrill, born in 

Ohio in 1841, was trained as a 

lawyer, and his firm was retained

by the Smith Bridge Company. 

Moving to San Francisco in

1869 in the hope of finding

a climate that might improve

his tuberculosis, he became

a Smith Bridge agent. After

founding the Pacific Bridge

Company in 1870 at Vallejo,

Gorrill secured a major contract 

for a bridge at Oroville in 1871, 

and thereafter built a number of 

important covered bridges, of

which the Powder Works Bridge

still survives in Santa Cruz,

California. The company soon 

moved to Oakland but also owned a mill yard in San Francisco that it used for precutting truss 

timbers, just as Smith Bridge Company itself was doing back in Ohio. After several years, Pacific 

Bridge built fewer timber Smith trusses and more iron bridges. Gorrill was not a builder in the usual 

sense, although he probably had a hand in preparing bridge plans. Through his contracting, the 

Smith truss became established as an important bridge form in California, and another prominent 

builder, A. S. Miller, brought it to Oregon. Gorrill died in 1874 of typhoid fever, although Pacific 

Bridge Company and its corporate successors remained an important player in the construction field

into the 1960s, long after the Smith truss had been forgotten.31 

Figure 6.13 Emmett L. Kennedy was photographed around 1935 holding a model he built in 1872 to help his family secure bridge contracts.

Courtesy of National Society for the Preservation of Covered Bridges. 

Three generations of the Kennedy family 

of Rushville, Indiana, built nearly sixty

covered bridges, mostly in the eastern

part of the state. Archibald M. Kennedy, 

born in 1818 in North Carolina, moved 

with his family to Indiana in 1825 and 

began working as a general carpenter in 

the 1840s. His first major bridge job was 

at Dunlapsville, Indiana, in 1870, with

his twenty-two-year-old son Emmett

assisting. Archibald retired in the mid1880s to continue a long-standing interest

in state politics. Meanwhile, another son, 

Charles F., had become involved in the 

bridge-building business, and Emmett’s

own sons, Karl and Charles R., later joined

the family business. At first the Kennedys 

170 Covered Bridges and the Birth of American Engineering 
 

 

 

used local timber but later purchased Michigan white pine. They preferred to prefabricate the truss 

parts at their work yard in Rushville. While many Indiana counties began favoring iron bridges 

after 1890, the Kennedys were called into service again to build covered bridges after the destructive

flood of 1913 wiped out bridges in the region. They built their last covered bridge in 1918. 

The Kennedys almost always used the 

Burr-arch truss, and their bridges are 

notable for the perfect form of the

arches. Their trusses used a two-part 

top chord with the posts notched

through the space in between, instead

of the usual one-piece top chord

with the posts mortised into the

bottom face.32 The posts, therefore,

had relish on the ends—referring to 

the extension of a timber to prevent 

shear from undoing a joint—and

this allowed the braces to be dapped 

with confidence into the posts fairly 

near the panel point, resulting in

an efficient transmission of stress

with minimal bending moments.

Their brace-post daps used double

tables for maximal efficiency with

minimal section loss. The wide area 

on top of their chords also allowed

the Kennedys to do away with sway 

bracing in the upper corners of the

roadway, relying instead on the large 

bearing area of the tie beams to

serve as wind bracing. To the casual 

observer, however, the most distinctive

feature of a Kennedy-built bridge is 

its finish. The portals have graceful

arches and are ornamented with roof 

brackets and scroll-sawn millwork.

The sides are neatly clapboarded, and 

the exteriors are painted white. While 

the Kennedy’s last few bridges lacked 

decorative millwork, they still retained

the arched portals, clapboards, and

white paint. Kennedy bridges are

widely recognized as among the most 

beautiful covered bridges ever built.33 

Figure 6.14 Forsythe Bridge (1888) in Rush County, Indiana, is typical of

Kennedy family framing and exhibits the beautiful portal that is a hallmark

of Kennedy construction. Top: 6.14a) HAER IN-106-12 and Above: 6.14b) 

HAER IN-106-9, James Rosenthal, photographer, 2004. 

Builders and Practices 171
 

Horace King of Georgia was born a slave in 

South Carolina in 1807 and showed aptitude 

for carpentry and heavy construction at

a young age. John Godwin, a prominent

building contractor, purchased King at the age 

of twenty-three, and they eventually moved

to Girard (now Phenix City), Alabama. In

1832–33, King and Godwin built a threespan, 600-foot Town lattice truss high over the 

Chattahoochee River at Columbus, Georgia, 

and this spectacular bridge secured King’s

reputation as a master craftsman. He went

on to build major bridges and handled other 

types of heavy construction, too. In choosing 

the Town lattice, King may have followed

an example set by Ithiel Town himself, who

built some well-known early prototypes in the 

Carolinas. King used the Town lattice as far 

afield as northeastern Mississippi during an

association with contractor Robert Jemison Jr. 

of Tuscaloosa, Alabama. 

Figure 6.15 Horace King (ca. 1850) was able to successfully pursue 

an independent bridge building career after being freed from

slavery in 1846. Daguerreotype ca. 1855 from the collection of 

the Columbus Museum, Columbus, Georgia; Museum purchase. 

King was freed in 1846, which allowed him to pursue a career as an independent contractor.34 The

Civil War wreaked havoc on the South’s road system, and Horace King was involved in the rebuilding

effort. Since many of his bridges were on major traffic arteries, none of them survive today. His 

son, Washington W. King, also became a builder, and at least two of his covered bridges still exist. 

It is hard to evaluate Horace King’s structural contributions with no surviving bridges to inspect. 

His legacy, instead, is as an example of a former slave who was able to contribute significantly to 

the built environment and economy of the South at a time when African Americans were often 

restricted from such opportunities.35

Elias McMellen, born in Lancaster County, Pennsylvania, in 1839, had built his first bridge by 

the age of twenty-one. After service in the Civil War, during which he rose to the rank of captain, 

he returned to bridge building in Lancaster. He built over thirty bridges in his career but also 

constructed other types of structures and owned a hotel. Although he used stone and iron for several

bridges, McMellen is best known for his immaculately framed Burr-arch truss covered bridges. 

Eleven of these remain and most still carry traffic.36 Captain McMellen died in 1916, but he is 

well remembered for his many contributions to the built heritage of southeastern Pennsylvania, a 

region rich in covered bridges. 

The perfection of the arches is the most obvious feature of McMellen’s bridges. Many builders 

found the arches of a Burr-arch truss difficult to lay out, so close inspection often reveals slight 

irregularities. There are no such problems in McMellen’s bridges, which stand as some of the finest 

examples of Burr-arch truss framing. 

172 Covered Bridges and the Birth of American Engineering 
Figure 6.16 Elias McMellen’s bridges, like the Kauffman’s Distillery Bridge (1874) in Lancaster County, Pennsylvania,

are known for their perfectly formed arches. Joseph Conwill, photographer, 1980. 

Nichols M. Powers was one of Vermont’s best-known builders, with at least fifteen covered highway 

bridges to his credit. Four of these remain.37 He also did railroad work, which may have involved 

bridges, but apart from his work in Maryland little evidence of this facet of his career remains. 

Born in 1817 in a section of Pittsford, Vermont, that later became part of Proctor, he spent most 

of his life in Clarendon until his death in 1897. 

In 1837, while still a minor, Powers built his first bridge, a 

Town lattice truss in Pittsford Mills. He tried other trusses 

but favored the Town lattice for most of his work. In 1855, he 

bridged Schoharie Creek at North Blenheim, New York, with 

a 210-foot single span using the Long truss plus arch.38 Until

its loss to Hurricane Irene in 2011, this bridge had the longest 

clear span of any covered bridge in America.39 Powers traveled

to Maryland in 1866 where he superintended construction of a

railroad bridge being built over the mouth of the Susquehanna

River at Havre de Grace. After this lengthy sojourn away from

home, he returned to Vermont for good but remained active 

as a bridge builder through 1880. His youngest son, Charles 

F. Powers, born in 1850, entered the bridge-building field, too, 

assisting his father at Havre de Grace while still a teenager.40 

Figure 6.17 Clarendon, Vermont, resident

Nichols M. Powers was among the state’s most

prominent bridge builders. Courtesy of National

Society for the Preservation of Covered Bridges. 

Builders and Practices 173 
The Town lattice truss is more standardized than other designs, and the bridges of any given builder

are only rarely so distinctive as to be identifiable on sight, as is sometimes the case in other building 

traditions. However, a close look shows that Powers brought sophisticated thought to his bridges. 

The 1880 Brown Bridge at Shrewsbury, Vermont, for example, has chord planks of variable sizes. 

The typical standard for early Town lattices was nominal 3 x 10 inches everywhere. In Brown 

Bridge, the lattice planks and the top chords (both primary and secondary) are the usual 3 x 10 

inches, but the bottom primary chord measures net 3 x 11-1/2 inches and the bottom secondary 

chord is 3 x 11 inches. These member dimensions help compensate for section loss due to splices, 

since the bottom chords are in tension. Powers also took care to use long chord sticks, which added 

overall strength to the bridge. 

The wooden trusses erected by the Smith Bridge Company, established in 1867, were competitive 

against iron-bridge manufacturers into the late nineteenth century because of Robert W. Smith’s 

efficient use of wood in his trusses. Not only was Smith’s truss innovative, but his methods of 

manufacture were, too. While the Howe truss was sometimes prefabricated, especially for use

on railroads, the Smith truss made almost exclusive use of the nation’s new large-scale industrial 

organization. Smith trusses found east of the Mississippi were mostly prefabricated at the company 

yards in Ohio. In California, Smith licensee William Henry Gorrill prefabricated the trusses at his 

San Francisco yard. It was possible for a builder to obtain Smith patent rights and cut the timbers 

himself, but more often the pieces were cut at the plant even if a local contractor did the construction.41 

Figure 6.18 The Smith Bridge Company of Toledo, Ohio, shipped the parts for a patented Smith truss to local communities

for other contractors to erect. Local contractor W. T. Washer built the Wheeling Bridge in Gibson County, Indiana, in 1877. 

Joseph D. Conwill, photographer, 2003. 

174 Covered Bridges and the Birth of American Engineering 
 

With the Smith Bridge Company the distinction between fabricator and erector, which is so

important in metal-bridge history, is encountered in timber. The Smith Bridge Company competed

directly against local builders. It was not the only large-scale company building timber highway 

bridges, but it was almost certainly the biggest, even though there were no known Smith Bridge 

Company bridges in New England or New York. The company’s work was centered in Ohio and 

Indiana, where it was a major player. The Smith Bridge Company also began offering iron bridges 

at an early date and switched to iron exclusively toward the end of the nineteenth century. Under 

a new name, the Toledo Bridge Company, it lasted until 1901, when it was swallowed up by the 

newly formed American Bridge Company.42 

Jonathan Parker Snow was bridge engineer for the Boston and Maine Railroad (B&M) and

was responsible for the continued construction of covered railroad bridges into the first decade

of the twentieth century when most other roads had turned to steel.43 Born in Concord, New

Hampshire, in 1848, he received formal training at the Thayer School of Civil Engineering, from

which he graduated in 1875. After trying several different branches of engineering, he turned to

bridges in 1880 and began working for the B&M in 1888. This line served a region rich in spruce

construction timber, and Snow was convinced that timber bridges were still economical. Indeed,

in 1895, the B&M still had over a thousand timber bridges of every kind: trestles, stringers, pony

trusses, through trusses, and deck trusses. 

Snow was a tireless advocate for 

wood, even in the face of his

profession’s nearly complete acceptance of steel, and continued 

to design new covered railroad

bridges almost until his retirement in 1911. He used the double 

Town lattice truss, patented by

Ithiel Town in 1835, as further

developed by David Hazelton

for the Boston and Lowell Railroad, a B&M predecessor. For a 

few bridges, however, he cleverly 

included a large laminated arch

within the two lattice webs to

carry the live load. The extra care

he devoted to proportioning timber sizes to loads is an interesting 

facet of his work; the planks in his

lattices increase in width toward 

the ends of his bridges. Snow

continued to practice engineering

as a consultant until his death

in 1933.44 

Figure 6.19 Wright’s Bridge (1906) over Sugar River near Newport, New Hampshire,

combined a heavy laminated arch for the live load with a stiffening Town lattice truss for

the dead load. It is a fine example of the careful design work of J. P. Snow for the Boston

and Maine Railroad. HAER NH-35-5, Jet Lowe, photographer, 2003. 

Builders and Practices 175
 

 

Arthur Clayton “Art” Striker was bridge superintendent for Lane County, Oregon, and oversaw the 

construction of dozens of covered bridges. Born in 1885 at Brighton, Ontario, he moved with his 

family to Oregon at the age of six. His father, Aaron Noble Striker, was a noted builder of covered 

bridges and other public works, and A. 

C. Striker worked with him on some of 

his projects. He joined the Lane County

highway department in the early 1920s 

just as the county was becoming firmly 

committed to the idea of building

bridges with its own labor instead of 

using outside contractors. At this time 

the covered bridge was still the standard

solution to Oregon’s rural-road needs. 

Striker soon became the county’s bridge

superintendent and worked with the

county engineer and various trusted

on-site supervisors, especially Miller

Sorensen.45 Striker preferred using

Howe trusses, often with one-piece

hewn chords that were sometimes

of gigantic proportions. The bottom

chords of the existing Pengra Bridge, 

for example, measure 16 inches x 18

inches x 126 feet. Most of the bridges 

had beautifully proportioned portals

with classic, elliptically arched entries, 

were clad in board-and-batten siding, 

and were neatly painted white.46 A. 

C. Striker retired in 1950 just as the 

covered bridge era was drawing to a

close, and he died in 1962.47 

Figure 6.20 Pengra Bridge (1938) is typical of the many bridges built in the

1930s in Lane County, Oregon, under the supervision of A. C. Striker. HAER

OR-119-4, Jet Lowe, photographer, 2004. 

Figure 6.21 Milton Graton repaired the Whittier Bridge (1871) in 

Carroll County, New Hampshire, using traditional techniques. The 

cables form part of a temporary suspension system used to support 

the bridge during the work. Joseph Conwill, photographer, 1983. 

Milton S. Graton was a pivotal figure 

in the twentieth-century covered

bridge preservation movement. Born

in 1908, he spent the early part of

his life at a variety of jobs, including 

timber hauling and rigging. After being

called upon to help dismantle a covered bridge in New Hampshire in the 1930s and marveling at 

the high quality of workmanship he saw in the structure, he became interested in covered bridge 

construction. In the late 1950s, Graton began moving and repairing covered bridges, dedicating 

himself to using traditional techniques. He then built an all-new covered bridge at Woodstock, 

Vermont, in 1968–69 and several others afterwards in other areas. Graton built his bridges entirely 

176 Covered Bridges and the Birth of American Engineering 
on land and often moved them into

place over their rivers using oxen and 

a capstan. There is so far no evidence 

that this method was used in the past, 

but it generated much public interest. 

Figure 6.22 Top: 6.22a) The work done by Tim Andrews during the rehabilitation of Gilpin’s Falls Covered Bridge in Cecil County, Maryland, carefully 

ensured the preservation of historic details. Above: 6.22b) Traditional timberframing tools used in carving out the step in a vertical post on the Gilpin’s 

Falls project include (left to right): a framing chisel, a corner chisel, a ca. 1930 

line bevel, and a urethane carver’s mallet. Will Truax, photographer, 2009 

Many covered bridges owe their

continued existence to his timely repairs,

often performed under very tight

budgetary constraints. Before Graton, 

it was accepted practice to add steel to 

covered bridges or to modify the trusses

because there were few people working 

with bridges in the mid-twentieth

century who were knowledgeable about

traditional woodworking. Destructive 

repair practices are still common, but 

Graton showed that in most cases it is 

possible to restore covered bridges using

techniques that the original builders

would have recognized. He inspired

a new generation of timber framers

dedicated to traditional covered bridge 

work. Milton Graton died in 1994, but 

his son Arnold M. Graton was closely 

involved in his projects and continues 

the family business.48 

Timothy Andrews is among the

foremost skilled timber framers working

with covered bridges today. Born in

1959 in Littleton, New Hampshire,

he is descended from a long line of

woodworkers from Nova Scotia who

were involved with sawmilling, ship

and church building, and other major 

projects. Andrews grew up familiar with

covered bridges because his grandparents

lived next to one in Lancaster, New

Hampshire. He became a carpenter as soon as he was out of high school, specializing at first in highquality interior finish work. His parents happened to buy property adjacent to Milton Graton’s land 

in 1979, and Graton became aware of Andrews’s talents. He asked Tim to build him a timber-truss 

frame for a water-tower tank and was so impressed with the quality of the work that he hired him for a 

variety of other projects, including covered bridge construction, rigging work, and masonry dam repair. 

Builders and Practices 177
As of 2011, Andrews has built, repaired, or salvaged fifteen covered bridges, either on his own or with

others. He built a new covered bridge at Ashland, New Hampshire, completed while working for 

Arnold Graton, and executed major repairs to the Cilleyville and the Ashuelot Upper Village bridges 

in New Hampshire, the Bennett Bridge in Maine, and Hall’s Bridge in Vermont. Andrews is careful 

to save as much original historic timber as possible and to restore bridges to their as-built conditions, 

without introducing modern materials. He has worked on a variety of other timber-framing projects,

too, such as repairs to roof trusses for an old theatre in Boston’s Back Bay and the construction of a 

large sugar house deep in the woods of Andover, New Hampshire, where there was no road access. 

The covered bridge builders discussed in this chapter were among the best known, but there were 

hundreds of others in America. Their ability to build so many useful, graceful, and long-lasting 

structures of wood had a significant impact on the American landscape. 

178 Covered Bridges and the Birth of American Engineering 
Endnotes

Builders and Practices 179 

1 A widespread and picturesque piece of folklore has builders winning a contract by presenting a wellbuilt model and standing on it. See, for example, Richard Sanders Allen, Covered Bridges of the Middle

Atlantic States (Brattleboro, Vt.: Stephen Greene Press, 1959), 89, and Allen’s same comments on James

F. Tasker in Rare Old Covered Bridges of Windsor County (Brattleboro, Vt.: The Book Cellar, 1962),

32–33.

2 J. Parker Snow, “Wooden Bridge Construction on the Boston and Maine Railroad,” Journal of the


Association of Engineering Societies 15, no. 1 (July 1895): 39.


3 For example, Canadian builder Albert E. Smye was based in the fishing port of Alma, New Brunswick,

where he specialized in wharfs and warehouses as well as bridges. Nichols Powers, a famous Vermont

builder, also did rigging, quarrying, and railroad work and owned a cheese factory. Stephen Gillis

and John Gillis, No Faster Than a Walk: The Covered Bridges of New Brunswick (Fredericton, New

Brunswick: Goose Lane Editions, 1988), 17–18. On Nichols Powers, see “Brown Bridge,” HAER No.

VT-28.

4 On Lewis Wernwag, see Richard Sanders Allen, Covered Bridges of the Middle Atlantic States

(Brattleboro, Vt.: Stephen Greene Press, 1959), 14–16, and F. E. Griggs Jr., “Colossus Bridge Designer

Lewis Wernwag,” Structure Magazine (October 2004), 34–36. On William Henry Gorrill, see Lola

Bennett, “William Henry Gorrill and the Pacific Bridge Company,” Covered Bridge Topics (Fall 2010), 

5–6.

5 Many details are provided in Lee H. Nelson’s excellent book, A Century of Oregon Covered Bridges


1851-1952 (Portland, Oreg.: Oregon Historical Society, 1960).


6 Observations of building styles are from visits made by the author, who saw every covered bridge in

North American over a ten-year period from 1966–77. For an example of a typical Lancaster County

Burr-arch truss, see “Pine Grove Bridge,” HAER No. PA-586. For a representative Berks County Burrarch truss, see “Dreibelbis Covered Bridge,” HAER No. PA-587. In regard to Somerset County’s Burrarch trusses, Theodore Burr described the practice of mitering the brace-post joints in his 1817 patent

text, but he seems not to have followed this method himself, so the origin of the Somerset style is unclear.

7 For an example of a Linn County Howe truss, see “Larwood Bridge,” HAER No. OR-124, while


“Pengra Bridge,” HAER No. OR-119, is a typical Lane County Howe truss.


8 For examples of the Long truss in central and eastern Maine, see Joseph D. Conwill, Maine’s Covered

Bridges (Charleston, S.C.: Arcadia, 2003), 58–63, 93–95, 108, 111, 113–14, and 122. The name

“Long’s plan” was known as far west as Franklin County, but it is uncertain if the term referred there to

the true Long patent.

9 It was once thought that Paddleford designed his truss in the early 1840s, but it now appears that he

built one as early as 1834 over the Connecticut River between Monroe, New Hampshire, and McIndoe

Falls, Vermont.

10 The cited construction cost of Bath-Haverhill Bridge comes from Rev. David Sutherland, Address

Delivered to the Inhabitants of Bath With an Historical Appendix by Rev. Thomas Boutelle (Boston:

Geo. C. Rand & Avery, 1855), 73. Town records are incomplete, so it is unclear whether the stonework

for the foundations was included. For additional information see: “Bath-Haverhill Bridge,” HAER

No. NH-33; “Eldean Bridge,” HAER No. OH-122; “Dreibelbis Covered Bridge,” HAER No. PA-587;

“Forsythe Covered Bridge,” HAER No. IN-106; “Johnson’s Mill Bridge,” HAER No. OH-127; and

“Brown Bridge,” HAER No. VT-28. See also Nelson, Century of Oregon Covered Bridges, 168, 200.

11 For a description of the mischief a truly unskilled builder could do with a Howe truss, see the letter

by C. H. Wright in Engineering News 30 (November 9, 1893), 376–77, reproduced in Covered Bridge

Topics (Summer 2008), 11. 
Endnotes

12 A 1962 date is sometimes cited erroneously for the Émery-Sicard Bridge of St-Maurice-de-Dalquier,

but this represents the date of major repairs; the construction date was actually 1946. On the

Quebec colonization bridges, see Gérald Arbour, et al., Les Ponts Couverts au Québec (Quebec: Les

Publications du Quebec, 2005). For background on the colonization movement itself, which required

the construction of special bridges, see Joseph D. Conwill, “Return to the Land: Quebec’s Colonisation

Movement,” History Today (April 1984), 16–21.

13 Quebec’s “colonization bridges” have held up surprisingly well over the years. Sixty-nine still exist, and

the majority still carry traffic. They tend to sag slightly because the bearing surface of spikes is much

less than that of treenails so the spikes cut into the wood. Even constructing these bridges required a

body of specialized knowledge, such as clinching some of the spikes to prevent the lattice planks from

separating. Untrained Civilian Conservation Corps labor also built a few bridges in the western United

States, but the crews appear to have had some experienced help.

14 Terry E. Miller has recorded extensive details of bids received by one Ohio county in The Covered


Bridges of Coshocton County, Ohio: A History (Kent, Ohio: by the author, 2009).


15 Techniques for splitting stone changed around 1830, as James L. Garvin has documented. Previously,

stonecutters chiseled a line of small square holes into the stone, into which they inserted wedges.

Later, stone cutters adopted the plug drill, which created round holes. Stone split by the earlier method

may be observed in the abutments and pier of the Bath-Haverhill Bridge (1829) at Woodsville, New

Hampshire. See James L. Garvin, “Appendix A: Notes on Materials and Construction Techniques of

Bath-Haverhill Covered Bridge,” in “Bath-Haverhill Bridge,” HAER No. NH-33, 2002, and also his

book, A Building History of Northern New England (Hanover, N.H.: University Press of New England,

2001), 42–47.

16 Hackmatack (alternatively hacmatac or hack) is a regional term used in the Maritimes and New

England for this versatile species. The butt area of the trunk with major roots attached was favored

for producing ships’ knees. The name hackmatack is thought to derive from a Native American word

meaning “snowshoe wood.”

17 For the history of Kennebec Bridge, see “Maine’s Covered Bridge Past,” Covered Bridge Topics (Winter

2001), 6–7. On the use of green lumber, see J. W. Buchanan’s recollections quoted in Richard Sanders

Allen, Covered Bridges of the Middle West (Brattleboro, Vt.: Stephen Greene Press, 1970), 27–28. See

also “Taftsville Bridge,” HAER No. VT-30.

18 Milled lumber was readily available after about 1830, at least for shorter lengths, but sometimes handhewn lumber continued in use in remote, rural areas. For example, some hand-hewn lumber was used

by Jerome Moot as late as the first decade of the twentieth century for bridges in the Dry Brook Valley

of Ulster County, New York, although it may have been reused from previous structures.

19 This is the case at Taftsville Bridge, in Windsor County, Vermont. A number of Oregon covered


bridges have single-hewn chord sticks with sawn braces and counters.


20 Historians of timber framing note a change in work practice shortly before 1830. In the older scriberule method, every piece was custom cut to the place it was to occupy. In the square-rule method,

standard pieces were cut to a reference line and were interchangeable. It might seem from this

procedure that the scribe-rule method of layout continued to be used even in a late period. This must

have been the case for those bridges using traditional joinery that also had features such as timber sizes

proportioned to the load or varying panel lengths. See Jan Lewandoski’s remarks on Blenheim Bridge

in Timber Framing 102 (December 2011), 23–24. Very little is known about the actual techniques

in the work yard. It is surprising, for instance, that covered bridges only rarely show marriage marks.

Illinois builder Jacob Allaman used standard templates for his Burr-arch truss posts, which strongly

suggests that he used square-rule framing. See Thelma Eaton, The Covered Bridges of Illinois (Ann 

Arbor, Mich.: Edwards Brothers, 1968), 21. James L. Garvin notes clear structural evidence for square180 Covered Bridges and the Birth of American Engineering
 

Endnotes

rule layout in the tie beams, wind braces, and rafters of Bath-Haverhill Bridge in Woodsville, New

Hampshire; see Garvin, “Appendix A.” Curiously, evidence for scribe-rule framing can be found in the

non-covered Howe trusses of New Brunswick, which sometimes show marriage marks. They date from

the first half of the twentieth century, a hundred years after square-rule framing was introduced, and

they use a truss form that would easily have allowed standardization.

Builders and Practices 181 

21 Builders also commonly carried rifles, shotguns, and fishing equipment to the work site; see Nelson,

Century of Oregon Covered Bridges, 139. The question of whether bridge timber was usually finished

with an adze or a broadaxe has been much discussed by timber framers in recent years, although tool

marks seem to indicate that the adze was frequently used.

22 For a photograph of such a machine in use, see Richard Sanders Allen, Covered Bridges of the Northeast

(Brattleboro, Vt.: Stephen Greene Press, 1957), 26.

23 Contemporary descriptions of covered bridge construction are rare. One of the best comes from

Oregon bridge builder Ole Haldorson, interviewed by Bill Cockrell in 2006; see “Ole Haldorson,

Oregon Bridge Builder: An Interview,” Covered Bridge Topics (Winter 2013), 3–10. See also David

Stephenson’s 1830s account as quoted in Herbert Wheaton Congdon, The Covered Bridge (Middlebury,

Vt.: Vermont Books, 1959), 83; Theodore Burr’s letter describing the construction of McCall’s Ferry

Bridge in 1815 in “Theodore Burr on the Challenges of Building McCall’s Ferry Bridge,” Covered

Bridge Topics (Winter 2009), 9–11; J. W. Buchanan’s recollections quoted in Allen, Covered Bridges

of the Middle West, 27–28; various photographs from the Archives Nationales du Québec shown

in “Did They Build the Covered Bridges on Land First, or Over the Water?” Covered Bridge Topics

(Summer 2011), 16 (although the bridge shown may not have been housed); and several descriptions

quoted in Nelson, Century of Oregon Covered Bridges. George E. Gould provides useful construction

notes that were probably based on information from interviews with builder Karl Kennedy in Indiana 

Covered Bridges Thru the Years (Indianapolis: Indiana Covered Bridge Society, 1977). See also the

1905 photograph of construction of a covered railroad bridge in Vermont in Claire Dunne Johnson,

St. Johnsbury (Charleston, S.C.: Arcadia, 1996), 61; note especially the stack of pre-bored lattice planks

waiting to be installed.

24 Allen’s Covered Bridges of the Middle West is excellent on Stone and Boomer and other railroad

contractors; see especially pages 114–20. See also Kramer A. Adams, Covered Bridges of the West

(Berkeley: Howell-North, 1963), 43.

25 This practice complicates research on covered railroad bridges. For example, the uncertainty about the

building date of the Shoreham Railroad Bridge in Addison County, Vermont, is due to the fact that it was

moved to its current site from places unknown, although the housing style resembles that of several former

railroad bridges in Connecticut and Rhode Island. “Shoreham Railroad Bridge,” HAER No. VT-32.

26 This is a regional practice sometimes found from the upper South through Ohio. The two-part top

chords also allowed Chenoweth to place the brace-post joint directly at the panel point, but this

advantage is partly lost by the fact that the brace-chord joint at the bottom is offset from the panel

point by the thickness of the floor beam. The building record on Chenoweth, however, is incomplete

because there are only two surviving bridges.

27 Biographical information from Randy Allan, Lemuel Chenoweth, 1811–1887: Bridging the Gaps

(Parsons, W.Va.: McClain, 2006). See also “Barrackville Bridge,” HAER No. WV-8, and Emory

L. Kemp and J. Hall, “Case Study of Burr Truss Covered Bridge,” Engineering Issues: Journal of

Professional Activities 101, no. 3 (1975): 391–412. A case study of the restoration of the Philippi Bridge

appears in Emory L. Kemp, “Restoration Techniques for American Covered Bridges,” Proceedings of the

International Historic Bridges Conference, Columbus, Ohio, August 27–29, 1992, 318–31. The existing

covered bridge at Carrollton is also sometimes credited to Chenoweth, but Allen states it was not built

by him. A brother, Eli, worked with Lemuel on many bridges but is much less well known.
 

Endnotes

28 Dann Chamberlin, “Joseph J. Daniels and His Indiana Covered Bridges,” paper presented at North

Central College, Naperville, Ill., January 1958, 20.

29 Gould, Indiana Covered Bridges, 14–17. Daniels refers to this practice in his specifications for a

wooden-truss bridge in Morgan County, Indiana, written in 1900, preserved in the Indiana Historical

Society, Indianapolis; a typescript copy is in the National Society for the Preservation of Covered

Bridges Archives, Concord, N.H., “Builders and Patents” drawer, “J. J. Daniels” file.

30 It has been widely reported that the tie rods pass through the post-chord tenon and serve to replace


treenails, but close examination proves this to be untrue. The joints are treenailed in the usual way,


although the treenails are not visible from inside the bridge because they are covered by the bearing


plate for the upper lateral bracing.


31 On Gorrill, see “Powder Works Bridge,” HAER No. CA-313, and Bennett, “William Henry Gorrill

and the Pacific Bridge Company.” For more on A. S. Miller, see Lee H. Nelson, A Century of Oregon

Covered Bridges, 1851–1952 (Portland: Oregon Historical Society, 1960).

32 Some Ohio builders also used a two-part top chord, but the one-piece chord was much more common

in Burr-arch trusses. For more on the Kennedys and on the Burr-arch truss in general, see Joseph D.

Conwill, “Burr Truss Framing,” Timber Framing 78 (December 2005), 4–11.

33 See “Forsythe Covered Bridge,” HAER No. IN-106, and Gould, Indiana Covered Bridges, 11–14.


Gould provides a useful chronological table of Kennedy bridges divided according to which family


members worked on them. See also Allen, Covered Bridges of the Middle West, 64–69.


34 While 1848 is often given as the date of his emancipation, that date is based on King’s recollection in

his later years when his memory may have been faulty. Contemporary documentation shows that the

date was 1846. On King generally, see John S. Lupold and Thomas L. French Jr., Bridging Deep South

Rivers: The Life and Legend of Horace King (Athens, Ga.: University of Georgia Press, 2004).

35 Local tradition credits Horace King with the construction of the existing Red Oak Creek Bridge in

Meriwether County, Georgia, but there is no written documentation supporting this attribution. See

“Red Oak Creek Bridge,” HAER No. GA-138.

36 This figure does not include the Pool Forge Bridge; although sometimes credited to McMellen, it shows

structural evidence of having been built by someone else. Unfortunately, one of the most beautiful of

the surviving bridges, the Pine Grove Bridge, has been compromised by the removal of the abutments

and floor system and the addition of steel beams. It was extensively recorded in “Pine Grove Bridge,”

HAER No. PA-586. 

37 His first name has been widely misunderstood as “Nicholas,” but contemporary records, including his

original signature, prove that it was “Nichols.”

38 The use of an integral arch with the Long truss was very unusual, but otherwise the truss of Blenheim

Bridge was close to the patent type. It had counterbrace wedges intended for prestressing, which were

located at the tops of the counterbraces, although they were mounted transversely to the chords, not

parallel with them as in the usual Long form.

39 The clear span had been shortened by repair and stabilization work. See “Blenheim Bridge,” HAER

NY-331. Bridgeport Bridge in Nevada County, California, was a near tie for the longest single-span

record and is the undisputed champion now that Blenheim is gone. On this complicated question, see

“Blenheim versus Bridgeport Revisited,” Covered Bridge Topics (Winter 2009), 16, and “Bridgeport

Covered Bridge,” HAER No. CA-41.

40 Charles F. Powers later did railroad bridge work in Maine, apparently using the Howe truss, but he

died at the age of thirty and is not well known today. See “Charles F. Powers, Bridge Builder,” Covered

Bridge Topics (Spring 2003), 3. 

182 Covered Bridges and the Birth of American Engineering
Builders and Practices 183 

41 Jackson County, Ohio, builders followed this practice of obtaining Smith patent rights but cutting the

timber themselves. See Miriam Wood, The Covered Bridges of Ohio (Columbus, Ohio: by the author,

1993), 34. Locust Creek Bridge in Pocahontas County, West Virginia, is probably another example, as

it is far afield and displays minor differences in framing from the usual highly standardized Smith type.

A practice developed in Kentucky of referring vaguely to trusses of the Warren type as “Smith,” but

these trusses were not connected with the Smith Bridge Company and differ so widely from the patent

type that they are not really part of the tradition.

42 Another company that successfully made the transition from timber to metal bridges was Kellogg

and Maurice of Athens, Pennsylvania, builder of the famous covered bridge over the Delaware River

between Columbia, New Jersey, and Portland, Pennsylvania, which was lost to high water in 1955. The

Champion Bridge Company of Wilmington, Ohio, is another example. It remains in business, and one

of its covered bridges still survives.

43 Boston and Maine was not, however, the last railroad to build covered wooden bridges. The Chicago,

Milwaukee, St. Paul, and Pacific (“the Milwaukee Road”) was still building them as late as 1938.

44 On Snow’s career, see “Wright’s Bridge,” HAER No. NH-35. The designation “Town-Pratt” found

in some books to describe the double Town-lattice form is erroneous, because T. Willis Pratt had no

involvement with the development of this design.

45 Striker’s bridges are sometimes credited to his on-site supervisors; for example, Miller Sorensen is often

cited as the builder of Mapleton and other bridges for which he had direct charge. See the interesting

interview with Sorensen in The Bridge Tender (Summer 1980), 3–5.

46 The portal style is thought to have been derived from bridges built by Lord Nelson Roney. See Nelson,

Century of Oregon Covered Bridges, 192.

47 Few details of Striker’s life have been found considering how recently he lived. See “Pengra Bridge,”

HAER No. OR-119; “Striker Services Held Wednesday,” Siuslaw News (Florence, Oreg.) August 30,

1962, 4. Bill Cockrell also provided information, including his 2006 interview with Ole Haldorson,

and Bill Morgan, Lane County Engineer, kindly tracked down some leads.

48 A comprehensive biography of Milton Graton remains to be written. Graton’s own book, The Last 

of the Covered Bridge Builders (Plymouth, N.H.: Clifford-Nicol, 1978), gives details of many of his

construction and repair projects. 

Chapter 7
 

The Preservation and Future of


Covered Bridges in the United States


by Justine Christianson and Christopher H. Marston 

Figure 7.1 “Many a bashful swain has found his tongue in the darkness of a covered bridge!” reads the caption on the back of

this photograph. Constructed in 1853 in Tompkins County, New York, the Newfield Bridge was rebuilt in 1972. John L. Warner,

photographer. Courtesy of Richard Sanders Allen Collection, National Society for the Preservation of Covered Bridges. 

During the tumultuous first half of the twentieth century, when increasing immigration, 

the Great Depression, and worldwide events like World Wars I and II changed both 

the American landscape and the American way of life, local communities hailed their 

covered bridges as symbols of a bygone, simpler era. As one unnamed writer for The Christian 

Science Monitor proposed,

It may be that covered bridges recall more peaceful times for many. They may bring

memories of carefree days when boys dove from the bridges’ abutments into cool water

below. Too, there’s many a man today who remembers how the hollow caverns of the

bridges’ interiors made wonderful places to hear the echo of their voices. They’d laugh,

hoot, and holler ’til three boys sounded like 30.1 

The Preservation and Future of Covered Bridges in the United States 185
Covered bridges evoked both pleasure (the title “kissing bridges” was bestowed on them because 

of the private moments they afforded young lovers) and fear (the experience of passing through a 

dark, shadowy tunnel). For many, they were also tangible reminders of home, of life in rural and 

small-town America. Burrell Burke, a reporter, explained, 

To me the covered bridge means the way to home. Home, with a loving, gray-haired mother

bustling about in preparation of the evening meal, and father with his newspaper, reading 

by the light of the kerosene lamp . . . . It brings back memories of carefree childhood days 

when this bridge, so unattractive to me now, was a marvel, a mystery, and was approached 

with a feeling of awe and peril . . . . The old bridge was then a link with the future; now 

it remains a symbol of the past.2

As a powerful symbol and reminder of the American past, the covered bridge became an object 

worthy of preservation through both private and government efforts well before formal federal 

preservation laws, such as the 1966 National Historic Preservation Act, were enacted. 

The number of standing covered bridges has steadily decreased from the type’s heyday in the midnineteenth century. According to preeminent covered bridge historian Joseph Conwill (perhaps 

the only person to have visited all the surviving covered bridges in the United States), there are 

currently 672 historic covered bridges remaining in the country, of which approximately half have 

been heavily modified.3 In contrast, Richard Sanders Allen reported 1,617 extant covered bridges in

1954, far fewer than the approximately 2,000 purportedly standing only five years earlier. Between 

1959 and 1965, another 188 were lost.4

Figure 7.2 Built in 1859, the ten-span Conowingo Bridge crossed the Susquehanna River in Maryland. This photograph from 

ca. 1925 shows the new steel trusses being constructed in the background while the original wooden Burr-arch trusses are 

being dismantled. Courtesy of Richard Sanders Allen Collection, National Society for the Preservation of Covered Bridges. 

186 Covered Bridges and the Birth of American Engineering 
 

The rapid rate of loss can be attributed to a

number of factors. Periodic large-scale flooding

has destroyed many covered bridges. Spring

flooding in Vermont in 1927 and 1928, for

example, resulted in the loss of wooden spans, 

the majority of which were replaced by steeland-concrete bridges as the state decided to

modernize its transportation infrastructure.

The Christian Science Monitor reported the

modernization was a “systematic program of

replacement to supplant wood with steel and

concrete,” an effort that was not unnoticed by 

local historical societies and covered bridge

enthusiasts. Yet, there were compelling reasons 

not to replace covered bridges in kind. Steel

bridges were an economical choice that could 

accommodate the heavier loads of automobile 

traffic. Concerns about sparks from locomotives setting fire to railroad covered bridges and heavy 

winds knocking down bridges, as well as the declining availability of wood in some regions, were 

other motivating factors for not building new covered bridges in place of the old.5

More recently, a number of New England covered bridges were destroyed or seriously damaged 

by flooding caused by hurricanes Irene and Lee in 2011. As many as forty bridges in five states 

were damaged. Two significant losses were the Blenheim Bridge in New York, a National Historic 

Landmark, and the Bartonsville Covered Bridge in Vermont. The Blenheim Bridge, built by Nichols

Powers in 1855, had one of the longest clear spans of any surviving covered bridge in the world and 

was one of only six surviving double-barrel covered bridges in the United States, but the structure 

could not withstand the violent flood waters of the Schoharie River. A video of the destruction of 

the Bartonsville Bridge was captured by a local resident and went viral on social media following 

the storm, becoming a symbol of Mother Nature’s destruction. Unlike Blenheim, Bartonsville was 

insured by the town of Rockingham and has since been replaced with a modern covered bridge. 

However, these storms reveal the vulnerability of historic bridges set in low-lying flood zones and 

highlight the need for securing bridges to their abutments.6

Figure 7.3 Historically, flooding frequently resulted in

covered bridges being washed downstream. The North

Enosburg Covered Bridge spanning the Missisquoi River

in Franklin County, Vermont, floated downstream during a

1927 flood. Courtesy of Richard Sanders Allen Collection,

National Society for the Preservation of Covered Bridges. 

The modernization of the U.S. highway system and changing requirements for transportation

structures impacted the survival of covered bridges. The advent of increasingly heavy vehicles along 

with the rising overall numbers of vehicles in use resulted in the establishment of rigorous standards

governing the design and construction of transportation structures. By the mid-twentieth century, 

lightly traveled local roads were increasingly being replaced by wider ones capable of moving greater

numbers of automobiles at higher speeds, and bridges had to be able to accommodate the greater 

demands. In the early 1950s, the Ohio State Highway Department undertook a concerted effort 

to remove the forty remaining state-owned covered bridges, citing safety concerns. E. M. Bollerer, 

assistant bridge inventory engineer, stated in The Christian Science Monitor, “we’re getting rid of 

them [covered bridges] as fast as possible.” He went on to explain, “They are all past their age limit 

The Preservation and Future of Covered Bridges in the United States 187 
now. As one after another goes, we don’t get very much complaining from sentimental people any 

more. Of course, anyone with any love of historical lore hates to see them go. But people now are 

more interested in highway safety. They want safer and newer bridges.” Although many covered 

bridges were removed in the name of progress and to maintain safety standards, their place in the 

American collective memory ensured that preservation efforts started early in the twentieth century.7

Figure 7.4 Following road realignment in 1929, the Humpback Bridge in Alleghany County, Virginia, was bypassed and a new steel

truss bridge was built, seen in the distance. HAER VA-1-11, Jack Boucher, photographer, 1971. 

Studying Covered Bridges 

As early as the 1890s, covered bridges were seen as “antiquities” worth being inventoried. Around 

the turn of the twentieth century, covered bridge “collecting” became popular. This often took

the form of traveling to as many covered bridges as possible and photographing them or amassing 

covered bridge postcards. By the mid-twentieth century, concerns about the attitude of government 

and transportation officials toward covered bridges, as well as the rapid rate of loss, led to increasing 

preservation efforts. As Leo Litwin, who in 1948, two years before serving as the first president of 

the National Society for the Preservation of Covered Bridges, warned, “the day is fast approaching 

when this interesting bit of Americana will be no more.” Thus, throughout the twentieth century, 

systematic studies and inventories of covered bridges were undertaken as a way to create a lasting 

record of extant covered bridges.8 

Rosalie Wells’s Covered Bridges in America, published in 1931, is one early inventory. While Wells 

waxed poetic about the solidity of the covered bridges built by her pioneer forebears, she also 

systematically listed notable extant covered bridges state by state. She presented the location and 

basic dimensions of each bridge along with any stories or legends associated with the structure 

and ample photographs. Other early books, like Clara E. Wagemann’s 1931 Covered Bridges of 

New England and Adelbert Jakeman’s 1935 Old Covered Bridges, focused on examining the role 

188 Covered Bridges and the Birth of American Engineering 
of covered bridges in American history and listing extant bridges in particular regions, although 

both neglected to include builder or designer information. Conspicuously lacking from this early 

scholarship was any identification of truss types and analysis of the structures. That shortcoming was

remedied by the work of Richard Sanders Allen (1917–2008), who systematically studied covered 

bridge truss types and organized covered bridges in his writings by truss type rather than solely by 

location. Allen’s development of more rigorous methods influenced other scholars and can be seen 

in Herbert Wheaton Congdon’s The Covered Bridge: An American Landmark Whose Romance, 

Stability, and Craftsmanship are Typified by the 

Structures Remaining in Vermont (1941).9 

Allen became interested in covered bridges

around the age of twenty and educated himself 

by reading widely, researching patents, and

engaging in voluminous correspondence with

local residents, historical societies, and other

knowledgeable persons. In the 1940s, he began 

inventorying covered bridges and studying the 

trusses, initially publishing a census of extant 

structures in 1946 in Covered Bridge Topics, a 

mimeographed sheet with information about

covered bridges that he produced six times a

year beginning in 1943. Allen started Topics as 

a way to disseminate information on covered

bridges after his correspondence became so great

that he could no longer respond to individual letters personally. He went on to publish a number 

of books on covered bridges, including Covered Bridges of the Northeast (1957), Covered Bridges 

of the Middle Atlantic States (1959), Covered Bridges of the South (1970), and Covered Bridges of 

the Middle West (1970), which are still standard texts in the field. While following the general 

historiographical trend of looking at bridges by region, Allen also introduced discussions of truss 

type in these works. By studying and focusing on truss types, scholars elevated the covered bridge 

from mere nostalgic artifact to significant engineering structure.10 

Figure 7.5 Richard Sanders Allen is justifiably known as the

“father of covered bridge history.” Courtesy of National Society

for the Preservation of Covered Bridges. 

The work of Philip and Betsy Clough paralleled that of Allen. The Cloughs proposed compiling an 

exhaustive list of all covered bridges still standing in the United States and assigning each bridge 

a unique identifying number. This list was eventually released in 1956 as the Guide to Covered 

Bridges of the United States. Three years later, the National Society for the Preservation of Covered 

Bridges (NSPCB) published the World Guide to Covered Bridges based on the Cloughs’ Guide. 

The publication included bridges in Canada, Europe (mainly Austria, Switzerland, and Germany), 

and Asia (mostly China). Regular updates to the guide have been made since the initial 1959 

publication, the latest in 2009. Each bridge listed in the World Guide has been assigned a unique 

number, with additional information provided such as the location, truss type, basic dimensions, 

builder (if known), and any other available historical information. Bridges that have been removed 

or lost due to weather, arson, or dismantling are deleted from the database. While “lost” bridges are 

removed from the World Guide, information about them is being maintained through the efforts 

The Preservation and Future of Covered Bridges in the United States 189 
of Bill Caswell and Trish Kane and their “Covered Spans of Yesteryear” Web site.11 

Figure 7.6 HABS architects measured the Howe truss

bridge spanning the Salt Fork River in Champaign 

County, Illinois, only days before its collapse. HABS 

photographer Chauncey Buck captured the remains of

 the bridge on April 13, 1934. “It makes my hair stand

on end when I think of how we galloped across that 

bridge, stamping vigorously to keep warm,” said 

team member Ralph Varney. “It must have come

very close to being our ‘Bridge of San Luis Rey.’ ” 

HABS IL-25-19, Chauncey Buck, photographer, 1934. 

Another early documentation effort was that by the Historic American Buildings Survey (HABS), 

a federal program established in 1933 to document the nation’s built environment through largeformat photographs, hand-measured drawings, and written reports. As part of its early efforts, 

HABS recorded forty-six covered bridges, twenty-one of which are no longer extant. While the 

documentation was sometimes cursory and typically did not include information about the trusses, 

it provided an early record of bridges that were disappearing from the American landscape.12 

The Covered Bridge Preservation Movement 

Organizations devoted to preserving covered bridges exist on both the national and local levels. 

The National Society for the Preservation of Covered Bridges, as the name suggests, has dedicated 

itself to the plight of covered bridges across the country. Organized in early 1950 by a group of 

covered bridge enthusiasts in Boston, Massachusetts, the society was incorporated in 1954 with 

Leo Litwin (1909–87) as the first president. A Russian immigrant and pianist with the Boston 

Pops Orchestra, Litwin had some influence with Boston’s elite. The group started with around one 

hundred members but now numbers five hundred across North America. Due to the geographic 

location of the president and organizing members, the membership has been concentrated in

New England, but the society’s scope has always been national in focus. In addition to collecting 

information about covered bridges, which has become the basis of the group’s archives as well as the 

Cloughs’ work and the World Guide, the society has worked to preserve the covered bridges that 

continue to disappear from the American landscape. This has taken the form of raising awareness 

by holding covered bridge festivals and meetings at covered bridges. In 1966, for example, the 

society organized the first New England Covered Bridge Festival, spanning three days over an early 

August weekend near Keene, New Hampshire. The festival included automobile tours of the area’s 

six covered bridges, a lantern-slide presentation, and a lecture on covered bridges.13

The NSPCB’s preservation philosophy, as articulated by David Wright, its late president, is that 

as “venerable antiques,” the bridges “should be treated as such; that is to say, with great respect 

for the technology which produced them in the first place, and with equal respect for the superb 

190 Covered Bridges and the Birth of American Engineering 
craftsmanship which is often on display within them.” Consequently, the organization is at “the 

forefront of those arguing for the use of traditional materials and procedures in Covered Bridge 

renovation projects.” Preservation efforts undertaken by the organization include letter-writing 

campaigns and meetings at bridge sites in order to raise awareness and educate local government 

officials and citizens about the historic nature of the bridges as well as to exert political pressure.14

Figure 7.7 Goodhue/Tannery Bridge in Enfield, New Hampshire, was the object of an intense, multi-year preservation battle that

ended with its removal. Richard Sanders Allen, photographer, August 11, 1941. Courtesy of Richard Sanders Allen Collection,

National Society for the Preservation of Covered Bridges. 

One early preservation battle in which the NSPCB became involved centered on the Tannery Bridge

(also known as Goodhue) in the little town of Enfield, New Hampshire (population 1,600). The 

battle began after town officials developed a plan to improve the road on which the Tannery Bridge 

was located in order to bring it up to state transportation standards. New Hampshire regulations 

allowed municipalities to hand over roads and bridges that met state standards to the state for 

maintenance and control, thereby reducing the town’s financial obligations, but the bridge did not 

meet the requirements. Noting that the bridge was excluded from transfer to the state, the town’s 

women’s club took their concerns about the removal of the covered bridge to the state Federation 

of Women’s Clubs. That organization got Sen. Katharine Jackson to sponsor legislation authorizing 

the inclusion of covered bridges in existing provisions regarding the repair and maintenance of 

bridges and roads. The bill had a broad base of support and was passed, but not until after Enfield 

had decided the fate of its bridge. Residents voted to replace the bridge with a concrete and steel 

structure by a vote of ninety to forty-seven and also defeated a motion to put off the vote for a 

year until the state legislation could be passed. Undeterred, a group of citizens banded together to 

raise funds to dismantle the bridge and re-erect it elsewhere, forming a “Save-the-Bridge Fund” to 

which readers of the Reporter-Advocate (whose editor, Edward Bennett, served as coordinator of 

the preservation campaign) were urged to donate a dollar. Meanwhile, NSPCB members wrote to 

government officials, urging preservation. The preservation advocates decided not to use nostalgia 

to advance their cause, but instead resorted to economic reasoning, pointing out that it was cheaper 

The Preservation and Future of Covered Bridges in the United States 191 
to repair the bridge than tear it down and

build a new one. When the issue was brought 

before the town for a second vote, however, 

it was defeated, and the Tannery Bridge was 

removed in 1954.15 

The preservation of the Cornish-Windsor

Bridge represents a landmark case study in 

rehabilitation and a concerted preservation

effort by the NSPCB, although the eventual 

solution was not the one preferred by the

organization. A two-lane, two-span bridge

built across the Connecticut River in 1866, 

the Cornish-Windsor Bridge is the only

remaining notched Town-lattice truss as

well as the longest historic covered bridge in 

the country at 450 feet.16 In 1984, the New 

Hampshire Department of Transportation

announced that it planned to correct the

bridge’s increasing sag and replace the

deteriorated members with steel. In response,

the NSPCB began lobbying for a sympathetic

restoration of the bridge and commissioned 

engineer David C. Fischetti to provide a

structural analysis. In 1986, Fischetti developed a proposal to replace the lower chords, floor beams,

and bolster beams with glued laminated (glulam) timbers instead of traditional solid-sawn timbers. 

While purists, including the NSPCB, opposed the introduction of glulam, it was embraced by the 

New Hampshire and Vermont departments of transportation and State Historic Preservation Officers

as the best solution to both strengthen the bridge and keep it open with a fifteen-ton weight limit. 

According to Fischetti, glulam’s advantages were that it could be fabricated in longer lengths than 

available solid timber and, being an engineered product, could be manufactured and shipped more 

quickly. In addition, glulam was pressure treated, which controlled moisture content, minimized 

shrinkage, and extended the life of the structural members. The disadvantages were that glulam was

not a true in-kind replacement for historic timber members (newly cut Douglas fir would have been 

closer to the original material), and that long glulam members were difficult to handle, requiring 

expert precision to integrate them into existing truss fabric. Timber framer Jan Lewandowski

successfully accomplished the installation of the glulam timbers using a cable-stayed system with 

Dywidag bars during the construction phase. Fischetti’s system allowed work to continue through 

snow and ice over the winter of 1988–89 and achieved the positive camber needed to keep the 

bridge in use. Although possibly not an optimal choice for other projects, the glulam solution here 

achieved the goal of strengthening and upgrading the bridge structure, maintaining its profile in 

a historic landscape, and preserving an important highway crossing.17

Figure 7.8 The introduction of glulam lower chords and floor 

beams on the Cornish-Windsor Bridge, although opposed by

many preservationists, helped achieve the positive camber 

required to keep the bridge in use. James Garvin, photographer, 

December 1988 and June 1989. 

The NSPCB has had success in preserving other covered bridges and consulting on the most

192 Covered Bridges and the Birth of American Engineering 
 

 

 

sensitive ways to restore them, such as

the Contoocook Railroad Bridge in

Contoocook, New Hampshire, which

was in active service on the Concord and 

Claremont Railroad (later part of the

Boston and Maine) until 1962. After a

public effort to save it, the bridge ended 

up under the ownership of the New

Hampshire Department of Resources

and Economic Development (DRED) in 

1989. The agency did not have funding for 

maintenance and repairs, but the NSPCB 

developed a preservation project with

DRED (Jim Garvin, New Hampshire

state architectural historian, served as

point person), Barns and Bridges of New 

England (owned by Timothy Andrews),

and D. C. F. Engineering (owned by David

C. Fischetti), using funds from the society’s

Eastman-Thomas Fund for Covered Bridge

Preservation, which was established in the 

mid-1950s.18

Figure 7.9 The two-span, double-web Town lattice truss Contoocook 

Railroad Bridge was originally located on the Boston and Maine 

Railroad. It is one of only eight surviving covered railroad bridges 

in the United States and remains standing thanks to the multi-year 

efforts of preservationists working in partnership with the state 

from 1989 to 2007. HAER NH-38-5, Jet Lowe, photographer, 2003. 

Figure 7.10 The replacement bed timbers installed on Contoocook 

used a bolted coupling splice inspired by a technique developed for 

similar structures by Snow and Fletcher in the 1930s. Note the granite 

pedestal supporting the corbel. Will Truax, photographer, 2007. 

Garvin and DRED applied for federal

Transportation Enhancement (TE) grant

monies for fire retardant  and dry-pipe

sprinkler systems for the Contoocook

Railroad Bridge. In order to receive the

TE funds, an engineering study needed to 

be done to demonstrate that the railroad

bridge was safe for pedestrian use and in

good repair. David Fischetti completed the study and analysis for a fraction of his regular fee. The 

rehabilitation work was completed over a period of several years, with the NSPCB providing $110,000 

and Barns and Bridges donating services totaling approximately $50,000. The project involved cleaning

out a significant amount of debris that had accumulated in the four corners of the bridge, including 

a tree that had taken root. Once the bridge was cleaned out, it became apparent that the bed timbers 

and corbels were deteriorated and required replacement. In addition, in the area where the tree had 

taken root, the bottom chord was rotting. In order to replace the necessary components, each corner 

of the bridge had to be lifted and shored, using I-beams lent by the New Hampshire Department of 

Transportation. The rotten chord was spliced using a technique described by J. P. Snow and Robert 

Fletcher in 1932.19 Short granite pedestals were installed to replace thin cross blocks that had been 

crushed under each bed-timber assembly. The corbels (bolster beams) were replaced in-kind, using old 

growth, long-leaf southern pine. Once the engineering and repair work were complete, the TE grant 

of $129,000 funded the application of fire retardant and the installation of a sprinkler system, work 

The Preservation and Future of Covered Bridges in the United States 193 
 

carried out by a contractor. The NSPCB provided matching funds of $29,800 to complete the project, 

which was undertaken over a two-year period from 2005 to 2007.20 

In addition to the National Society for the Preservation of Covered Bridges, there are regionallyfocused groups that work to preserve and maintain the covered bridges within their areas. These 

groups, in general, promote interest in covered bridges and raise awareness about their significance. 

The activities of regional preservation groups can be broadly classified as collecting information 

about the covered bridges under their purview, publishing newsletters or magazines to educate both

their membership and the general public about covered bridges, holding covered bridge safaris and 

other social events, and advocating for their covered bridges. 

Regionally-focused preservation groups have augmented the collection of information on covered 

bridges started by the large-scale efforts of the Cloughs and Richard Sanders Allen. The executive 

committee of the Indiana Historical Society, for example, established a committee to research, 

document, and promote the preservation of the state’s covered bridges in March 1931. The resulting 

Covered Timber Bridge Committee solicited donations of materials about covered bridges and also 

asked each county for information on extant covered bridges. The materials it collected are still 

available to researchers in the William Henry Smith Library at the Indiana Historical Society. In 

1937, Robert B. Yule, the group’s first chairman, published Covered Bridges of Indiana, a pamphlet 

detailing the location of existing covered bridges, in collaboration with Richard C. Smith of the 

William Henry Smith Library.21

The New Hampshire Covered Bridge Association was established in 1957. One of its first tasks was 

to survey the sixty-one covered bridges then extant in the state. The resulting 1961 publication was 

produced in cooperation with the New Hampshire Department of Public Works and Highways 

and the New Hampshire Council of Regional Associations and consisted of a folder with a map 

showing the locations of covered bridges and 

brief descriptions. Signs were also erected

at each bridge site. The covered bridge

association, according to one newspaper

article, had “vigilante committees” keeping 

“watch over each of the 55 [covered bridges] 

still left standing” in the state.22 

In today’s Internet age, Web sites can serve 

as clearinghouses of information, such

as “Maryland Covered Bridges” at www. 

mdcoveredbridges.com, which was established

in August 2008 by James B. Smedley. While 

doing research on covered bridges in the state,

Smedley found that as many as 125 had once 

existed, and his website provides information 

on both the historic as well as the six extant 

covered bridges in the state.23 

Figure 7.11 The Allentown-Lehigh County Tourist and Convention 

Bureau of Allentown, Pennsylvania, published a “Covered Bridge

tour guide” for use in local heritage tourism. The pamphlet included a driving map showing the location of the county’s covered

bridges. The tour was promised to offer “each person, young

or old, male or female, an opportunity to blend the truth and

the imagination.” Pamphlet, date unknown, in HAER office files. 

194 Covered Bridges and the Birth of American Engineering 
 

 

Visiting covered bridges was a popular recreational activity in the first half of the twentieth century,

and covered bridge preservation groups held “covered bridge safaris” after 1950 that highlighted a 

region’s collection of covered bridges and thereby raised awareness of the importance of the structures.

It was not just preservation groups that used covered bridge safaris to raise awareness, however, as 

local communities and chambers of commerce soon realized that their covered bridges could be 

used in heritage tourism to boost the local economy. To guide visitors to the bridges, pamphlets 

and brochures were developed with maps showing bridge locations and providing some historical 

information. For example, the Theodore Burr

Covered Bridge Society of Pennsylvania,

incorporated in 1959, holds an annual covered 

bridge safari to a county or particular region in 

the state.24

Parke County, Indiana, is known as the “Covered

Bridge Capital of the World” because of its

thirty-one extant covered bridges, and it hosts 

one of the largest and longest-running covered 

bridge festivals. The festival was established

by volunteers in 1957 as a way to showcase

the county’s numerous covered bridges after

two were lost to flooding and a third faced

demolition. The first three-day festival attracted 

twenty-five hundred attendees. These initial efforts expanded when Judy Snowden and W. B.

Hargrave established the nonprofit Parke County Incorporated in 1961. The Covered Bridge Festival

Committee was part of the nonprofit and was charged with planning the festival, which focused not

only on covered bridges but also the county’s agricultural heritage. The festival included both bus 

tours of the county’s covered bridges and such characteristically American activities as a barbecue 

and a pancake breakfast. Parke County Incorporated continues to provide information on covered 

bridges to the public and oversees and organizes the Covered Bridge Festival, while also working 

with government officials on the preservation of covered bridges and occasionally donating funds 

to maintain, preserve, and rebuild them.25 

Figure 7.12 The Theodore Burr Covered Bridge Society of 

Pennsylvania visited Jonathan Speakman’s Mill No. 1 Bridge 

(1881) in Chester County as part of its 1974 annual safari. Courtesy of Theodore Burr Covered Bridge Society of Pennsylvania. 

Covered bridge preservation groups do not simply celebrate the past and distribute information; 

they also work to physically preserve their local bridges. On March 31, 1960, a group of amateur 

photographers began meeting monthly at the Zanesville, Ohio, home of Anita Knight and soon 

they realized they had a common interest in covered bridges. From this, the Southern Ohio Covered

Bridge Association was formed (so named because there was already a northern association); it 

became the Ohio Historic Bridge Association in 1996 and broadened its scope to the preservation 

of all types of historic bridges, becoming the first such organization in the nation. One of the 

association’s major projects, and a part of its articles of incorporation, was the purchase of the Salt 

Creek Covered Bridge in Muskingum County. The bridge had been bypassed by a welded-steel 

one and was no longer needed. Muskingum County transferred ownership to a farmer, but when 

the possibility arose that the farmer might demolish the bridge, the association acted to save it. 

Ownership of the bridge was returned to the county, and the association used Federal Highway 

The Preservation and Future of Covered Bridges in the United States 195 
Administration funds to do extensive repairs in the 1990s.26 

Figure 7.13 Thanks to the efforts of the Ohio Historic Bridge Association dating 

back to 1960, the Salt Creek Bridge continues to survive as a historic landmark in 

Muskingum County, Ohio. Preservationists across the country have volunteered 

their time to preserve covered bridges like this one. Left: 7.13a) David Simmons,

photographer, 1998; Above: 7.13b) HAER OH-127-1, Jet Lowe, photographer, 2004. 

The Government and Covered Bridge Preservation 

There have been successful state and federal government initiatives to promote covered bridge 

preservation. As early as the 1950s, the state of Massachusetts attempted to institute a policy of 

replacing covered bridges with new covered ones instead of building steel and concrete spans. 

Massachusetts Department of Public Works commissioner William F. Callahan (1891–1964)

became an advocate for the construction of new covered bridges as the state worked to preserve 

its few remaining ones. Reportedly influenced by a poem written by selectmen of the town of 

Charlemont about the original 1833 Bissell Bridge, Callahan approved the bridge’s replacement with

a new covered span despite initial plans for a modern concrete and steel bridge. In Callahan’s view, 

The covered bridge is a New England symbol of romance and the rich, romantic past. 

To tear one down without rebuilding a duplicate would be equal to desecrating ‘Old 

Ironsides’ or destroying Bunker Hill Monument. Furthermore, we can build replicas of 

covered wooden bridges that are more efficient than the 19th century originals, will last 

just as long as steel bridges, and also carry the loads.27

By 1951, the new, larger, covered bridge at Charlemont had been erected, and another was built in 

Sheffield in 1952, but the efforts died out by the mid-1950s.28

In 1959, the state of Maine became the first state to enact preservation legislation protecting its ten 

remaining covered bridges. The state also instituted a maintenance and rehabilitation program under

the State Highway Department and appropriated $50,000 for covered bridge renovation.29 Other

states have also developed bridge preservation plans that include covered bridges. In 1998, the state 

of Vermont established the Vermont Historic Bridge Program through a programmatic agreement 

among numerous state and federal agencies. Managed by the Vermont Agency of Transportation 

196 Covered Bridges and the Birth of American Engineering 
(VTrans), the program seeks to preserve the state’s historic covered, metal-truss, and masonry- and 

concrete-arch bridges and to recognize their economic, aesthetic, and educational value.30 One way 

it does this is though cooperative agreements between towns, VTrans, and the Vermont Division 

of Historic Preservation. By enrolling bridges in the program, towns agree to convey a preservation 

easement to VTrans, preserve the structure, and undertake specified maintenance while VTrans pays

for rehabilitation and restoration. Historic bridges owned by the state are automatically part of the 

program. In addition, the program assigns VTrans the responsibility of scheduling and undertaking

regular maintenance, rehabilitation, and restoration. If bridges in the program can no longer be 

used on highways, they are relocated and used for alternative transportation. 

The Historic Covered Bridge Committee, whose mission is to “insure that the historic integrity of 

Vermont’s covered bridges is preserved to the greatest extent possible,” oversees Vermont’s Historic 

Covered Bridge Preservation Plan. The committee is tasked with reviewing the condition of all 

covered bridges and making specific recommendations for their preservation. The plan establishes 

a priority-of-uses list for covered bridges (the highest priority being maintaining a bridge in use 

on roads with maximum preservation of structural members) and a priority-of-treatments list (the 

optimal treatment being retention of all historic materials).31 One of the members of the Historic 

Covered Bridge Committee is from the Vermont Covered Bridge Society.32

Twenty-three covered bridges have been rehabilitated in Vermont as part of this program from 2003

to 2013, assisted by funding from the National Historic Covered Bridge Preservation (NHCBP) 

Program. Several of these bridges remain in service. For example, the Cooley Covered Bridge in 

Pittsford, a Town-lattice truss, was rehabilitated in 2003. The rehabilitation involved installation 

of timber decking and siding and glulam floor beams, replacement of selected chord and lattice 

members, and repairs to the slate roof. While the use of glulam remains controversial in covered 

bridge circles, that treatment is consistent with the state’s priority of treatments.33 

Figure 7.14 In 2002, the HAER documentation team found the original lower chord, lateral bracing, and stone abutments of

Pine Grove Bridge in Lancaster County, Pennsylvania, as constructed by Elias McMellen in 1884, still intact. While the Pennsylvania Department of Transportation saved the Burr-arch trusses in 2008, they unfortunately replaced the lower timbers with

steel I-beam and removed all of the stonework, constructing new concrete abutments with a form liner surface treatment.

Top: 7.14a) HAER field photo, 2002; Above: 7.14b) Tom Vitanza, photographer, 2009. 

In recent years, other states such as Ohio, Indiana, and Oregon have also developed programs to 

evaluate, save, and preserve their covered bridges, making them a priority in statewide historicThe Preservation and Future of Covered Bridges in the United States 197 
bridge management plans.34 The commonwealth of Pennsylvania, however, has resorted to the use 

of steel I-beams in several of its replacement floor systems. While this methodology has kept several 

historic covered bridges in service with ten- to twenty-ton weight limits and original truss timber, 

it is an unfortunate trend. The use of steel compromises the integrity of the historic covered bridge, 

particularly because skilled engineers and timber framers are still able to use properly treated Douglas

fir timbers as a sensitive engineering solution. 

As Sheila Rimal Duwadi explains in chapter 2, the National Historic Covered Bridge Preservation 

program was created at the federal level in 1998. Preservation, research, and dissemination of information

are the primary goals of the NHCBP program, which it has achieved by allocating funds in two areas 

from 2000 to 2012. First, the program has provided funds to states to repair, rehabilitate, restore, and 

otherwise preserve covered bridges that are listed in or eligible for listing in the National Register of 

Historic Places. Second, the program has granted monies for education and research on restoration and

protection methods. In addition, the NHCBP program has funded the Historic American Engineering

Record’s initiative to document covered bridges, known as the National Covered Bridges Recording 

Project. HAER teams have documented more than eighty covered bridges, and that documentation has

formed the basis for additional work, such as the completion of a National Historic Landmark (NHL) 

Theme Study, multiple NHL nominations, and a traveling exhibition on covered bridges produced in 

conjunction with the Smithsonian Institution. In addition, a deeper understanding of covered bridge 

truss technology has become possible through the use of new technologies, such as laser scanning the 

bridges during documentation, state-of-the-art load- and environmental-testing, and the development 

of partnerships with such universities as Case Western Reserve, Johns Hopkins, and Bucknell.35 

Studies funded by the NHCBP program have tackled some of the key issues faced by those preserving

covered bridges, such as decay and fire. Slowing the decay of the timbers used in covered bridges 

is a significant challenge. Preservative treatments can be costly, however, and the chemicals used 

can leach over time, creating long-term environmental effects. In addition to natural factors, arson 

and vandalism threaten covered bridges. Fire retardant treatments have thus been developed to 

spray on covered bridges. These treatments form a layer of char when heated, protecting the wood 

underneath. While the treatments do not fire-proof the wood and do not extinguish a fire, they can 

make it more difficult for a would-be arsonist to set a structure on fire. Heat- or smoke-activated 

alarm systems and sprinkler systems for wood bridges have also been developed.36 

Preservation of covered bridges remains difficult, however. The complexity and inflexibility of 

government contracting and project-management systems discourages the hiring of the best

independent craftsmen and hinders nimble preservation action in emergency situations. Furthermore,

there are few specialized engineers and even fewer master carpenters capable of planning and

executing the type of sensitive, in-kind repairs preferred by the preservation community, a deficit 

compounded by a lack of instruction in America’s engineering schools in traditional building

techniques.37 As engineer Jim Barker succinctly states, 

It is important for an engineer who works in preservation to deeply respect the builders who

created these structures, and to preserve their original vision as closely as possible. A designer

who is concerned about our history, and who has taken the time to learn about Theodore

198 Covered Bridges and the Birth of American Engineering 
Burr, Louis Wernwag, Stephen Long, Hardy Cross, and etc., will probably do a better job on

a historic restoration than one who views the project as one more “profit center.”38 

The late David Fischetti, an engineer on several covered bridge preservation and rehabilitation 

projects, added these words on cooperation amongst professionals. 

Structural engineers with timber design experience must become actively involved in historic

preservation in order to save our remaining historic covered bridges. Highway department engineers

must seek out consultants with timber design experience. By working together, we can save an 

important part of our civil engineering heritage.39

The forthcoming publication Guidelines for Rehabilitating Historic Covered Bridges, being produced

jointly by the National Park Service and the Federal Highway Administration, will provide case 

studies of best practices in the preservation of covered bridges. As Tim Andrews stated in the 

opening plenary talk at the Second National Covered Bridge Conference in 2013, “What would 

the original builder/designer do if presented with the same problems? Finding solutions which best 

meet the goals and aspirations of both pragmatist and preservationist needs to be accomplished.”40 

Future 

The loss of the National Historic Landmark Blenheim Bridge to flooding in 2011 and the persistent 

threat of arson to other bridges stand as poignant reminders of the fragility of covered bridges. 

What is the future of these historic resources, which have such a hold on the American imagination?

Thanks to the efforts of individuals and covered bridge preservation societies, the development of 

best practices and rehabilitation guidelines, and the increasing historical awareness of transportation

officials and engineers, these structures, with their attendant cultural meanings, may long remain 

standing in the American landscape. 

The Preservation and Future of Covered Bridges in the United States 199 
 

Endnotes

1 “Covered Bridges Draw Visitors to Massachusetts,” Christian Science Monitor, April 19, 1955, 11.

2 Burrell Burke, “Reflections on a Covered Bridge,” Christian Science Monitor, February 16, 1955, 17.

3 Joseph Conwill defines a historic covered bridge as one built before 1930 in New England, before 1945

in other parts of the country east of the Rocky Mountains, and before 1960 in the West and Canada.

See Joseph Conwill, “Covered Bridge Truss Types,” Timber Framing 102 (December 2011): 14–21.

4 David Wright, correspondence with the authors, February 2012; “2000 Covered Bridges Still Remain

in Use,” Los Angeles Times, November 30, 1949, 21; “Land of Covered Bridges,” Chicago Daily Tribune, 

October 8, 1961, B10.

5 “Covered Bridge Leaving Main Vermont Roads,” Christian Science Monitor, February 18, 1932, 3; W.

Clifford Harvey, “Saving of Covered Bridges Possible,” Christian Science Monitor, October 22, 1938,

9; Miriam F. Wood and David A. Simmons, “Introduction,” in Covered Bridges: Ohio, Kentucky, West

Virginia (Wooster, Ohio: Wooster Book Company, 2007), 2–16.

6 A complete list of the covered bridges damaged in hurricanes Irene and Lee can be found at http:// 

www.coveredbridgesociety.org/news.html; “Lower Bartonsville Covered Bridge Collapses into the

Williams River in Vermont,” http://www.youtube.com/watch?v=WyO18one8fU.

7 E. M. Bollerer quoted in Helen Waterhouse, “Ohio Dooms Covered Bridge,” Christian Science

Monitor, November 23, 1953, 14. For a discussion of road construction, see Albert C. Rose, Historic

American Roads: From Frontier Trails to Superhighways (New York: Crown Publishers, 1976).

8 “Old Bridge Cult Gains,” Baltimore Sun, October 17, 1948, A16; quote from Leo Litwin, “Romance of

the Covered Bridge,” Christian Science Monitor, June 12, 1948, WM8.

9 Rosalie Wells, Covered Bridges in America (New York: William Edwin Rudge, 1931); Clara

Wagemann, Covered Bridges of New England (Rutland, Vt.: Tuttle Co., 1931); Adelbert Jakeman,

Old Covered Bridges: The Story of Covered Bridges in General, with a Description of the Remaining

Bridges in Massachusetts and Connecticut (Brattleboro, Vt.: Stephen Daye Press, 1935); Herbert

Wheaton Congdon, The Covered Bridge: An Old American Landmark Whose Romance, Stability, and

Craftsmanship are Typified by the Structures Remaining in Vermont (Brattleboro, Vt.: Stephen Daye

Press, 1941); Joseph Conwill and David Wright, telephone conversation with the authors, February 13,

2012.

10 Telephone conversation with Conwill and Wright; Wright, correspondence with authors, February 2012.

11 Telephone conversation with Conwill and Wright; David Wright, ed., World Guide to Covered Bridges, 

7th ed. ([Hillsboro, N.H.]: National Society for the Preservation of Covered Bridges, Inc., 2009). The

National Park Service produced a geo-referenced version of the World Guide in 2009–11, available

online through the National Center for Wood Transportation Structures, http://www.woodcenter.org/ 

CoveredBridges/. “Covered Spans of Yesteryear” can be found at www.lostbridges.org.

12 For more on the early years of HABS, see American Place: The Historic American Buildings Survey

at Seventy-five Years (Washington, D.C.: U.S. Department of the Interior, National Park Service,

2008), 17. The work done during the original HABS surveys occasionally led to subsequent confusion.

Two covered bridges once stood in Newton Falls in Trumbull County, Ohio, but only one—a Howe

truss no longer standing–was recorded by HABS. Researchers seeking photographs of the still extant

Newton Falls Covered Bridge, a Town lattice, have often become confused as a result.

13 Michael Strauss, “A Roof Above, River Below: A Weekend of Homage to Covered Bridges in New


Hampshire,” New York Times, July 24, 1966, 292; Jean Erickson, “Save a Covered Bridge,” Boston


Globe, July 24, 1966, A34.
 

200 Covered Bridges and the Birth of American Engineering
 

Endnotes

14 Wright, correspondence with authors, February 2012.

15 “Outsiders Are Helping in Save-Bridge Drive,” Hartford Courant, April 14, 1953, 8C; Edward Lathem,

“Battle in Enfield, N.H., to Save Covered Bridge,” Daily Boston Globe, March 7, 1954, C69.

16 The 450-foot measurement represents the length at the deck. The four-span Smolen-Gulf Bridge

(World Guide no. 35-04-64) in Ashtabula County, Ohio, built in 2008 by John Smolen, is the longest

non-historic covered bridge at 613 feet.

17 A detailed description of the Cornish-Windsor Bridge rehabilitation is found in David C. Fischetti,

Structural Investigation of Historic Buildings: A Case Study Guide to Preservation Technology for

Buildings, Bridges, Towers, and Mills (Hoboken, N.J.: John Wiley and Sons, Inc., 2009), 227–39.  See

also “Cornish-Windsor Covered Bridge,” HAER No. NH-8, and Laura S. Black, “Cornish-Windsor

Covered Bridge,” in Guidelines for the Rehabilitation of Historic Covered Bridges, ed. Thomas Vitanza

(Washington, D.C.: Government Printing Office, forthcoming).

 18 Wright, correspondence with authors, February 2012.

19 J. P. Snow and Robert Fletcher, “A History of the Development of Wooden Bridges,” Transactions of

the American Society of Civil Engineers 96 (1932): 351.

20 Tim Andrews, email to Christopher Marston, October 24, 2012.

21 The committee disbanded in 1960 and was replaced by the Indiana Covered Bridge Society, established

on September 8, 1963, with 150 charter members. The society focuses on the preservation of the

state’s remaining covered bridges; John C. Murray, letter to the authors, March 29, 2012. See also

Laurie Randall, Janet Schmidt, and Dorothy A. Nicholson, “Historical Sketch,” in Covered Timber

Bridge Committee Collection, 1930–1979 (archival finding aid, October 2009), Manuscript and

Visual Collections Department, William Henry Smith Memorial Library, Indiana Historical Society,

Indianapolis, Ind., available online at www.indianahistory.org/.

22 “New Hampshire Group Aims to Protect Covered Bridges,” Christian Science Monitor, September 24,

1957, 7; quote from Roger Greene, “Trend Grows to Retain Shed Covered Bridges,” Hartford Courant, 

November 27, 1958, 17; “New Folder Lists New Hampshire’s Covered Bridges,” Hartford Courant, 

April 16, 1961, 5B; Earl Banner, “Country Diary: Covered Bridges at a Glance,” Boston Globe, April 8,

1961, 22.

23 James B. Smedley, correspondence with the authors, April 2012.

24 Vera Wagner and Sylvester K. Stevens, the executive director of the Pennsylvania Historical and

Museum Commission, organized the first meeting of the Theodore Burr Covered Bridge Society, held

April 5, 1959. Stevens was concerned about the perception held by transportation officials that covered

bridges were impediments that needed to be removed and believed that creating an advocacy group

could slow the bridges’ removal. “Covered Bridges Revealed,” Hartford Courant, May 11, 1969, 4F;

Joyce Soroka, letter to the authors, March 30, 2012; see also the Web site of the Theodore Burr Covered

Bridge Society, of which Soroka is president, at www.tbcbspa.com.

25 “Roofed Bridge Fans Tour 25 in Indiana Fete,” Chicago Daily Tribune, October 21, 1957, 23;

“Hoosiers Plan Bridge Festival,” Chicago Tribune, October 7, 1963, B5; Michael Schafer, “Covered

Bridge County,” Chicago Tribune, October 10, 1965, I60; Cathy Harkrider, letter to the authors, March

28, 2012. Parke County Inc.’s Web site is www.coveredbridges.com.

26 David A. Simmons, “Restoration of the Salt Creek Covered Bridge,” booklet prepared by the Ohio

Historic Bridge Association to commemorate the rededication of the Salt Creek Covered Bridge,

September 10, 1998; David A. Simmons and Miriam Wood, letter to the authors, March 2, 2012. See

also the Ohio Historic Bridge Association Web site, http://oldohiobridges.com/ohba. 

The Preservation and Future of Covered Bridges in the United States 201 
Endnotes

27 Paul Kneeland, “Why Sheffield Is Going to Have a New Covered Bridge,” Daily Boston Globe, March 

11, 1951, A5.

28 The Charlemont Bridge was once again under consideration for replacement with a concrete and steel

bridge in the mid-2000s, but it was instead rehabilitated with the addition of steel rods. The Lower

Sheffield Bridge (World Guide no. MA/21-02-02#2X), spanning the Housatonic River, was a Pratt

truss built in 1952 and removed in 1988. For information on Callahan and the movement to build

new covered bridges, see “Poem Leads Bay State to Rebuild Covered Span,” New York Times, May 11,

1950, 31; “Covered Bridges Draw Visitors to Massachusetts,” Christian Science Monitor, April 19, 1955,

11; Bernard J. Malahan Jr., “Old Bridges Saved,” New York Times, April 26, 1953, X17; Lucia Mouat,

“National Society Boosts Antique Bridges,” Christian Science Monitor, December 11, 1962, 3; Richard

Sanders Allen, Covered Bridges of the Northeast (Brattleboro, Vt.: Stephen Greene Press, 1957), 69–72.

29 Joseph C. Ingraham, “Maine to Maintain its Covered Bridges,” New York Times, March 27, 1960,


XX13.


30 The Vermont Historic Bridge Program was established through a programmatic agreement between

the Federal Highway Administration, the Advisory Council on Historic Preservation, the Vermont

Agency of Transportation, the Vermont State Historic Preservation Office, and the Vermont Agency

of Natural Resources. The agreement permits inclusion of bridge types beyond covered bridges once

preservation plans for those bridge types have been established. The next plan will be for reinforced

concrete slab, T-beam, and through-girder bridges, although only one in the last category survives.

Robert McCullough, email to the authors, September 6, 2013.

31 See the Vermont Historic Bridge Program’s program agreement (1998) and Historic Covered Bridge

Preservation Plan (2003) at http://historicbridges.vermont.gov/.

32 William McKone, Joseph Nelson, and Edward Barna established the Vermont Covered Bridge Society

in February 2000 after the Cambridge Junction Covered Bridge was threatened by its poor state of

repair. The society has developed a bridge-watch program, dividing the state into bridge-watch areas

to monitor the condition of Vermont’s covered bridges. Joseph Nelson, letter to the authors, March 9,

2012.

33 Robert McCullough, email to the authors, September 28, 2012.

34 The Ohio Department of Transportation is creating an interactive map locating the state’s

historic bridges. For information on the state’s historic bridges, see http://www.dot.state.oh.us/ 

divisions/planning/environment/cultural_resources/historic_bridges. The Indiana Department of

Transportation funded a context study and survey as part of a programmatic agreement governing

historic covered bridges. See Mead and Hunt, Indiana Bridges Historic Context Study, 1830s– 

1965, Indiana Department of Transportation, 2007, available at http://www.in.gov/indot/files/ 

INBridgesHistoricContextStudy1830s-1965.pdf. Oregon has also developed a best-selling guide to the

state’s covered bridges. See http://www.oregon.gov/ODOT/HWY/BRIDGE/pages/covered_bridges. 

aspx.

35 Sheila Rimal Duwadi and James P. Wacker, “Covered Bridges in the United States and the

Preservation Program,” Proceedings of the 10th World Conference on Timber Engineering, Miyazaki,

Japan, June 2008, available at http://www.treesearch.fs.fed.us/pubs/34809; Philip C. Pierce, Robert

L. Brungraber, Abba Lichtenstein, and Scott Sabol, Covered Bridge Manual, publication no. FHWAHRT-04-098, U.S. Department of Transportation, Federal Highway Administration, April 2005. 

202 Covered Bridges and the Birth of American Engineering
 

Endnotes

The Preservation and Future of Covered Bridges in the United States 203 

36 Information provided by Jim Barker of J. A. Barker Engineering, Inc. One study funded by the

NHCBP program is Stan Lebow, Grant Kirker, Robert White, Terry Amburgey, H. Michael Barnes,

Michael Sanders, and Jeff Morrell, Guide for In-Place Treatment of Wood in Historic Covered and

Modern Bridges (U.S. Department of Agriculture, Forest Service, Forest Products Laboratory, in

cooperation with U.S. Department of Transportation, Federal Highway Administration, General

Technical Report FPL-GTR-205, March 2012), also available online at http://www.fhwa.dot.gov/ 

bridge/covered.cfm.

37 Telephone conversation with Wright and Conwill.

38 Jim Barker, “Restoration of a Covered Bridge over Troubled Waters and Underneath Calm Ones,”

Structure Magazine (October 2007), 22–25.

39 Fischetti, Structural Investigation of Historic Buildings, 210.

40 Timothy Andrews, “Rehabilitating 19th Century Bridges using 19th Century Solutions,” Second 

National Covered Bridge Conference, Dayton, Ohio, June 2013, available at http://www.woodcenter. 

org/2013-national-covered-bridge-conference/papers.cfm. 

Selected Bibliography
 

The following selection is only a portion of the available literature on covered 

bridges. Due to space constraints, this bibliography focuses on national and regional

studies, generally omitting studies of individual bridges. 

Books

Adams, Kramer A. Covered Bridges of the West, A History and Illustrated Guide: Washington, Oregon,

California. Berkeley, Calif.: Howell-North, 1963. 

Allen, Richard Sanders. Covered Bridges of the Middle Atlantic States. Brattleboro,

Vt.: Stephen Greene Press, 1959. 

______ . Covered Bridges of the Middle West. Brattleboro, Vt.: Stephen Greene Press, 1970. 

______ . Covered Bridges of the Northeast. Rev. ed. Brattleboro, Vt.: Stephen Greene Press, 1974. 

______ . Covered Bridges of the South. Brattleboro, Vt.: Stephen Greene Press, 1970. 

Auvil, Myrtle. Covered Bridges of West Virginia, Past and Present. 3rd ed. Parsons, W.Va.:

McClain Print Co., 1977. 

Baker, Jeanne. An Undercover Story: Covered Bridges of California. Chapel Hill, N.C.:

Chapel Hill Press, 2000.

Barna, Ed. Covered Bridges of Vermont. Woodstock, Vt.: Countryman Press, 1996. 

Brandenburg, Phyllis, and David Brandenburg. Kentucky’s Covered Bridges: Vanishing Kentucky Scenes.

Cincinnati, Ohio: Harvest Press, 1968. 

Brydon, Norman F. Of Time, Fire and the River: The Story of New Jersey’s Covered Bridges.

New Vernon, N.J.: New Vernon Business Service, 1970. 

Burk, John S. Massachusetts Covered Bridges. Charleston, S.C.: Arcadia Publishing, 2010. 

Caswell, William S., Jr. Connecticut and Rhode Island Covered Bridges. Charleston,

S.C.: Arcadia Publishing, 2011. 

Cockrell, Bill. Oregon’s Covered Bridges. Charleston, S.C: Arcadia Publishing, 2008. 

Cockrell, Bill, and Nick Cockrell. Roofs over Rivers: A Guide to Oregon’s Covered Bridges.

Beaverton, Ore.: Touchstone Press, 1978. 

Cohen, Stan. West Virginia’s Covered Bridges: A Pictorial Heritage. Charleston, W.Va.:

Pictorial Histories Publishing Co., 1992. 

Congdon, Herbert Wheaton. The Covered Bridge: An Old American Landmark Whose Romance,Stability,

and Craftsmanship Are Typified by the Structures Remaining in Vermont. Brattleboro, Vt.:

Stephen Daye Press, 1941.

Conwill, Joseph D. Covered Bridges. Oxford: Shire Publications, 2014. 

______ . Covered Bridge Across North America. St. Paul, Minn.: MBI, 2004. 

______ . Maine’s Covered Bridges. Charleston, S.C.: Arcadia Publishing, 2003. 

______ . Vermont Covered Bridges. Charleston, S.C.: Arcadia Publishing, 2004. 

Selected Bibliography 205
Eaton, Thelma. The Covered Bridges of Illinois. Ann Arbor, Mich.: Edwards Brothers, 1968. 

Edwards, Llewellyn Nathaniel. A Record of History and Evolution of Early American Bridges.


Berkeley, Calif.: University Press, 1959.


Evans, Benjamin D., and June R. Evans. New England’s Covered Bridges: A Complete Guide.


2nd ed. Lebanon, N.H.: University Press of New England, 2004. 

______ . Pennsylvania’s Covered Bridges: A Complete Guide. Pittsburgh, Pa.: University of

Pittsburgh Press, 1993. 

French, Thomas L., Jr., and Edward L. Covered Bridges of Georgia. Columbus, Ga.: Frenco Co., 1984. 

Fischetti, David C. Structural Investigation of Historic Buildings: A Case Study Guide to Preservation

Technology for Buildings, Bridges, Towers, and Mills. Hoboken, N.J.: John Wiley and Sons, 2009. 

Fitzsimons, L. Neal, et al. American Wooden Bridges. ASCE Historical Publication No. 4. New York:

American Society of Civil Engineers, 1976.

Gibbons, Faye. Horace King: Bridges to Freedom. Birmingham, Ala.: Crane Hill Publishers, 2002. 

Gould, George E. Indiana Covered Bridges Thru the Years. Indianapolis:

Indiana Covered Bridge Society, 1977. 

Graton, Milton S. The Last of the Covered Bridge Builders. Plymouth, N.H.: Clifford-Nicol, 1990. 

Guise, David. Abstracts and Chronology of American Truss Bridge Patents, 1817–1900.

Houghton, Mich.: Society for Industrial Archeology, 2009.

Hagerman, Robert L. Covered Bridges of Lamoille County, Vermont. Morrisville, Vt.: by the author, 1972. 

Haupt, Herman. General Theory of Bridge Construction. New York: D. Appleton and Co., 1851.

Hammer, Arthur F., ed. Romantic Shelters: A Supplement to the World Guide to Covered Bridges.

Marlboro, Mass.: National Society for the Preservation of Covered Bridges, 1989. 

Harvey, Max. The Covered Bridges of Parke County, Indiana. Montezuma, Ind.:

Wabash Valley Printing Co., 1959. 

Howard, Andrew R. Covered Bridges of Bennington County, Vermont: A Guide. Unionville, Conn.:

Village Press, 1997. 

______ . Covered Bridges of Connecticut: A Guide. Unionville, Conn.: Village Press, 1985. 

______ . Covered Bridges of Madison County, Iowa: A Guide. Unionville, Conn.: Village Press, 1998. 

______ . Covered Bridges of Maine: A Guide. Unionville, Conn.: Village Press, 1982. 

______ . Covered Bridges of Massachusetts: A Guide. Unionville, Conn.: Village Press, 1978. 

______ . Covered Bridges of Virginia: A Guide. Unionville, Conn.: Village Press, 1999. 

Jakeman, Adelbert M. Old Covered Bridges: The Story of Covered Bridges in General.

Brattleboro, Vt.: Stephen Daye Press, 1935. 

Kemp, Emory L. American Bridge Patents: The First Century (1790–1890). Morgantown:

West Virginia University Press, 2005.

______ . West Virginia’s Historic Bridges. Morgantown: West Virginia University Press, 1984. 

Kenyon, Thedia Cox, and Stan Snow. New Hampshire Covered Bridges. Sanbornville, N.H.:

Wake-Brook House, 1957. 

Ketcham, Bryan E. Covered Bridges on the Byways of Indiana. Lockland, Ohio: by the author, 1949. 

______ . Covered Bridges on the Byways of Ohio. Cincinnati, Ohio: by the author, 1969.

Knoblock, Glenn A. New Hampshire Covered Bridges. Charleston, S.C.: Arcadia Publishing, 2002. 

Krekeler, Brenda. Covered Bridges Today. Canton, Ohio: Daring Books, 1989. 

Laughlin, Robert W. M., and Melissa C. Jurgensen. Kentucky’s Covered Bridges. Charleston, S.C.:

Arcadia Publishing, 2007. 

Lewandoski, Jan, et al. Historic American Roof Trusses. Becket, Mass.: Timber Framers Guild, 2006.

206 Covered Bridges and the Birth of American Engineering 
Long, Stephen Harriman. Description of Col. Long’s Bridges, Together With a Series of Directions to Bridge

 Builders. Concord, N.H.: John F. Brown Printers, 1836. 

Lupold, John S., and Thomas L. French Jr. Bridging Deep South Rivers: The Life and Legend of Horace King.

Athens: University of Georgia Press, 2004. 

Marshall, Richard G. New Hampshire Covered Bridges: A Link with Our Past. Nashua, N.H.:

TDS Printing, 1994. 

McKee, Brian J. Historic American Covered Bridges. New York: American Society of Civil

Engineers Press, 1997. 

McCullough, Robert. Crossings: A History of Vermont Bridges. Barre, Vt.: Vermont Agency of

Transportation and the Vermont Historical Society, 2005.

Miller, Terry E. and Ronald G. Knapp, photography by A. Chester Ong. Covered Bridges:

Practical Crossings—Nostalgic Icons. Rutland, Vt.: Tuttle Publishing, 2014. 

Moll, Fred J. Covered Bridges of Berks County, Pennsylvania. Reading, Pa.: Reading Eagle Press, 2001. 

______ . Pennsylvania’s Covered Bridges. Charleston, S.C.: Arcadia Publishing, 2012. 

Moore, Elma Lee. Ohio’s Covered Bridges. Charleston, S.C.: Arcadia Publishing, 2010. 

Morley, S. Griswold. The Covered Bridges of California. Berkeley: University of California Press, 1938. 

Morse, Victor. Windham County’s Famous Covered Bridges. Brattleboro, Vt.: The Book Cellar, 1960. 

Nelson, Joseph C. Spanning Time: Vermont’s Covered Bridges. Shelburne, Vt.: New England Press, 1997. 

Nelson, Lee H. A Century of Oregon Covered Bridges, 1851–1952. Portland: Oregon Historical Society, 1960. 

______ . The Colossus of 1812: An American Engineering Superlative. New York:

American Society of Civil Engineers, 1990. 

O’Grady, Patrick. Replicate: The Rebuilding of the Corbin Covered Bridge in Newport, New Hampshire.

Concord, N.H.: by the author, 1998.

Patton, L. K., and R. W. MacGregor Laughlin. Kentucky’s Timbered Tunnels: A Presentation of Kentucky’s

Thirteen Covered Bridges. Fort Thomas, Ky.: Kentucky Covered Bridge Association, 1994. 

Petersen, Herman. The Covered Bridge. New York: Thomas Crowell Co., 1950. 

Petersen, Hegen. Kissing Bridges. Brattleboro, Vt.: Stephen Greene Press, 1965. 

Pope, Thomas. A Treatise on Bridge Architecture. New York: Printed for the author by Alexander Niven, 1811 

Pierce, Leola B. Covered Bridges in Virginia. Glen Rose, Tex.: Upstream Press, 2002. 

Reed, Robert. Indiana’s Covered Bridges. Charleston, S.C.: Arcadia Publishing, 2004. 

Sangree, Rachel Herring. “Covered Wooden Bridges: An Experimental and Numerical Investigation of

System and Component Behavior.” Ph.D. diss., Johns Hopkins University, 2006. 

Sangster, Tom and Dess L. Alabama’s Covered Bridges. Montgomery, Ala.: Coffeetable Publications, 1980. 

Schlotterbeck, Seth S. Covered Bridges of Preble County, Ohio. Eaton, Ohio: Preble County

Historical Society, 1994. 

Schneider, Norris F. Muskingum River Covered Bridges. Zanesville, Ohio: Southern Ohio

Covered Bridge Association, 1971. 

Sloane, Eric. American Barns and Covered Bridges. Mineola, N.Y.: Dover Publications, 2002. 

Smith, Elmer L., and Mel Horst. Covered Bridges of Pennsylvania Dutchland. Lebanon, Pa.: Applied Arts

Publishers, 1988. 

Swanson, Leslie C. Covered Bridges in Illinois, Iowa and Wisconsin. Moline, Ill.: by the author, 1960.

Town, Ithiel. A Description of Ithiel Town’s Improvement in the Construction of Wood and Iron Bridges:

Intended as a General System of Bridge-Building. New Haven, Conn.: S. Converse, 1821. 

Wagemann, Clara. Covered Bridges of New England. Rutland, Vt.: Tuttle Co., 1931.

Selected Bibliography 207 
Way, R. Bruce. The Life and Careers of William Henry Gorrill 1841–1874. Lanham, Md.:

University Press of America, 1996.

Weber, Wayne M. Covered Bridges in Indiana. Midland, Mich.: Northwood Institute, 1977. 

______ . The Covered Bridges of Parke County, Indiana. Indianapolis: Indiana Covered Bridge Society, 1980. 

Wells, Rosalie. Covered Bridges in America. New York: William Edwin Rudge, 1931. 

White, W. Edward. Covered Bridges of New Hampshire. Littleton, N.H.: Courier Printing Co., 1942. 

Whipple, Squire. A Work on Bridge Building Consisting of Two Essays, the One Elementary and General,

the Other Giving Original Plans and Details for Iron and Wooden Bridges. Utica, N.Y.: H. H.

Curtiss, Printer, 1847. 

______ . An Elementary and Practical Treatise on Bridge Building. Enlarged and Improved Edition of the

Author’s Original Work. 2nd. ed. New York: D. Van Nostrand, 1872. 

White, Vernon. Covered Bridges: Focus on Kentucky. Berea, Ky.: Kentucky Imprints, 1985. 

Wilson, Richard R. New York State’s Covered Bridges. Charleston, S.C.: Arcadia Publishing, 2004. 

Wood, Miriam F. The Covered Bridges of Ohio: An Atlas and History. Columbus, Ohio:

Old Trail Printing Co., 1993. 

Wood, Miriam F., and David A. Simmons. Covered Bridges: Ohio, West Virginia, Kentucky.

Wooster, Ohio: Wooster Book Co., 2007. 

Wright, David, ed. World Guide to Covered Bridges. 7th ed. National Society for the Preservation of

Covered Bridges, 2009. 

Zacher, Susan. The Covered Bridges of Pennsylvania: A Guide. Harrisburg: Pennsylvania Historical and

Museum Commission, 1994. 

Ziegler, Phil. Sentinels of Time: Vermont’s Covered Bridges. Camden, Maine: Down East Books, 1983. 

Articles and Journals 

Allen, Richard Sanders. “America’s Covered Bridges.” Consulting Engineer, April 1957, 92–100.
 

______ . “Crossings under Cover.” Trains, June 1955, 45–50.
 

______ . “Uncovering Covered Bridge Lore.” Profitable Hobbies, October 1948, 26–29, 56.
 

Beach, Ursula Smith. “Tennessee’s Covered Bridges, Past and Present.” Tennessee Historical Quarterly 28,


no. 1 (Spring 1969): 3–23.

Bennett, Lola. “From Craft to Science: American Timber Bridges, 1790–1840.” APT Bulletin

35, no. 4 (2004): 13–19. 

Bock, Eugene R. “The Covered Bridge and Indiana.” Indiana History Bulletin 37, no. 5 (1960): 5–28. 

Buonopane, S., S. Ebright, and A. Smith. “The Timber Trusses of R. W. Smith: History, Design and

 Behavior.” Proceedings of the Fourth International Congress on Construction History, Paris,

July 3–7, 2012, 599–606. 

Caston, Philip S. C. “Doing It the American Way: Federal Historic Building Recording in the

United States.” In Forschung und Praxis: Arbeitsberichte aus dem Fachbereich Bauingenieurund Vermessungswesen der Fachhochschule Neubrandenburg und befreundeter Institutionen.

Neubrandenburg, Germany: Fachhochschule Neubrandenburg, 2005, 63–97. 

Conwill, Joseph D. “Burr Truss Bridge Framing.” Timber Framing 78 (December 2005): 4–100. 

______ . “Covered Bridge Truss Types.” Timber Framing 102 (December 2011): 14–21. 

______ . “The Howe Truss Goes Low-Tech.” Timber Framing 85 (September 2007): 20–25. 

______ . “Long Truss Bridge Framing.” Timber Framing 87 (March 2008): 4–5. 

______ . “Oregon’s Covered Bridges in Context.” The Bridge Tender 4 (Winter 1983): 1–3. 

______ . “Paddleford Truss Framing.” Timber Framing 75 (March 2005): 12–15. 

208 Covered Bridges and the Birth of American Engineering 
 

 

 

Cooper, Theodore. “American Railroad Bridges.” Transactions of the American Society of Civil Engineers

21 (July–December 1889): 1–52. 

Covered Bridge Topics. A quarterly journal published by the National Society for the

Preservation of Covered Bridges. 1943 to present. 

Cummings, Hubertis M. “Theodore Burr and His Bridges across the Susquehanna.” Pennsylvania History

23, no. 4 (October 1956): 476–86. 

Diehl, John. “Bridges to the Past.” Timeline 15, no. 3 (May–June 1998): 30–51. 

Dreicer, Gregory K. “Building Bridges and Boundaries: The Lattice and the Tube, 1820–1860.”

Technology and Culture 51, no. 1 (2010): 126–63.

Fletcher, Robert, and J. P. Snow. “A History of the Development of Wooden Bridges.”

Transactions of the American Society of Civil Engineers 99 (1934): 314–408.

Garvin, James. “Wooden Bridges on the Boston & Maine Railroad.”

New Hampshire Division of Historical Resources, Publications, June 5, 2004.

Available at http://www.nh.gov/nhdhr/publications/documents/wooden_bridges_on_bm.pdf. 

Gasparini, Dario, and David Simmons. “American Truss Bridge Connections in the 19th Century. Part I:

1829–1850.” Journal of Performance of Constructed Facilities 11, no. 3 (August 1997): 119–129. 

______ . “American Truss Connections in the 19th Century. Part II: 1850–1900.” Journal of Performance

of Constructed Facilities 11, no. 3 (August 1997): 130–40. 

Gasparini, Dario, J. Bruckner, and F. da Porto. “Time-Dependent Behavior of Posttensioned Wood Howe

Bridges.” ASCE Journal of Structural Engineering 132, no. 3 (March 2006): 418–29. 

Gasparini, Dario, J. Bruckner, and C. Tardini. “G. W. Whistler and the Howe Bridges on the Nikolaev Railway,

1842-1851,” ASCE Journal of Performance of Constructed Facilities (June 22, 2015). 

Griggs, Francis E. “It’s a Pratt! It’s a Howe! It’s a Long! No, It’s a Whipple Truss!”

Civil Engineering Practice, Spring/Summer 1995, 67–85. 

______. “Colossus Bridge Designer Lewis Wernwag.” Structure Magazine, October 2004, 34-36. 

Guise, David. “Abstracts & Chronology of American Truss Bridge Patents.”

Society for Industrial Archeology Occasional Electronic Publication No. 1 (2009).

Available at http://www.sia-web.org/occasionalpub/electronic/pub1/SIAOccElectPub1.pdf. 

James, J. G. “The Evolution of Wooden Bridge Trusses to 1850.” Journal of the Institute of Wood Science

[London] 9, no. 3 (June 1982): 116–35, and 9, no. 4 (December 1982): 168–93. 

Jones, Harvie P. “The Town Lattice Truss in Building Construction.” Bulletin of the Association for

Preservation Technology 15, no. 3 (1983): 39–41. 

Kemp, Emory L. “Lemuel Chenoweth: Pioneer Bridge Builder.” Virginia Highway Bulletin 40

(March 1974): 13–16. 

______ . “Restoration Techniques for American Covered Bridges.” Proceedings of the International Historic

Bridges Conference (Columbus, Ohio), August 1992, 318–31. 

Kemp, Emory L., and J. Hall. “Case Study of Burr Truss Covered Bridge.” Engineering Issues: Journal of

Professional Activities 101, no. 3 (1975): 391–412. 

Kniffen, Fred. “The American Covered Bridge.” Geographical Review 41, no. 1 (January 1951): 114–23. 

Lamar, Dylan M., and Benjamin W. Schafer. “Structural Analyses of Two Historic Covered

Wooden Bridges.” Journal of Bridge Engineering 9, no. 6 (2004): 623–33. 

Levin, Ed. “Covered Bridge Truss Engineering.” Timber Framing 105 (September 2012): 10–15. 

“Lewis Wernwag, The Bridge Builder,” Engineering News 14 (August 15, 1885): 98-99. 

Long, Stephen H. “Remarks on the Jackson Bridge.” Journal of the Franklin Institute 4, no. 2

(August 1830): 110–12. 

Machtemes, Allison. “Investigation of the Structural Behavior of Historical Covered Timber Bridges.”

Master of Science thesis, Iowa State University, 2011.

Selected Bibliography 209
Marston, Christopher H. “Craftsmanship across the Cornfields: A Survey of Midwestern Covered Bridges.”

Structures Congress 2006: Structural Engineering and Public Safety, St. Louis (May 18–21, 2006). 

______ . “ ‘Covered Bridges: Spanning the American Landscape’ Traveling Exhibit Debuts in Harrisburg.”

Society for Industrial Archeology Newsletter 35, no. 2 (Spring 2006): 1–3.

Mill, Randall V. “The Covered Bridge in Oregon: A Continuing Tradition.” Western Folklore 7,

no. 2 (April 1948): 101–14. 

Mitchell, Harry E., Jr. “The Covered Bridges of Berks County.” Historical Review of Berks County 13,

no. 1 (October 1947): 2–13. 

Pease, George B. “Timothy Palmer, Bridge-Builder of the Eighteenth Century.”

Essex Institute Historical Collections 83, no. 2 (April 1947): 97–111. 

Prevost, Lewis M. “Description of Howe’s Patent Truss Bridge.” Journal of the Franklin Institute 3

(May 1842): 289–92. 

Robison, Jon. “Covered Bridges of Madison County.” Annals of Iowa 38 (Fall 1966): 414–26. 

Royce, Edmund Homer. “Covered Bridges of Vermont.” Vermont Life, Spring 1947, 12–17, 40. 

Sloane, Eric. “The First Covered Bridge in America.” Geographical Review 49, no. 3 (1959): 315–21. 

Snow, J. Parker. “Wooden Bridge Construction on the Boston & Maine Railroad.”

Journal of the Association of Engineering Societies 15 (July 1895): 31–43. 

Wilson, Raymond E. “The Story of the Smith Truss.” Covered Bridge Topics 25, no. 1 (April 1967): 3–5. 

Government Publications 

Avery, Floyd L. “Report of Covered Bridges in New Hampshire.” Concord:

New Hampshire Department of Public Works and Highways, 1965. 

Bennett, Lola. “Covered Bridges NHL Context Study.” U.S. Department of the Interior, National Park

Service. 2012. Available at: http://www.nps.gov/nhl/learn/specialstudies/CoveredBridges.pdf. 

______ . “Humpback Bridge” (National Historic Landmark Nomination).

U.S. Department of the Interior, National Park Service. 2012.

Available at: http://www.nps.gov/nhl/news/LC/spring2012/HumpbackBridge.pdf. 

______ . “Knight’s Ferry Bridge” (National Historic Landmark Nomination).

U.S. Department of the Interior, National Park Service. 2012.

Available at: http://www.nps.gov/nhl/news/LC/spring2012/KnightsFerry.pdf. 

______ . “Brown Bridge” (National Historic Landmark Nomination).

U.S. Department of the Interior, National Park Service. 2013.

Draft available at: http://www.nps.gov/nhl/news/LC/fall2013/BrownBridge.pdf. 

______ . “Duck Creek Aqueduct” (National Historic Landmark Nomination).

U.S. Department of the Interior, National Park Service. 2013.

Draft available at: http://www.nps.gov/nhl/news/LC/fall2013/DuckCreek.pdf. 

______ . “California Powder Works Bridge” (National Historic Landmark Nomination).

U.S. Department of the Interior, National Park Service. 2014.


Draft available at: http://www.nps.gov/nhl/news/LC/spring2014/CAPowderWorksBridge.pdf.
 

Pierce, Phillip C., Robert L. Brungraber, Abba Lichtenstein, Scott Sabol, J. J. Morell, and S. T. Lebow.

Covered Bridge Manual. U.S. Department of Transportation, Federal Highway Administration.

Publication No. FHWA-HRT-04-098. April 2005. 

Patents 

Burr, Theodore. U.S. Patent No. 2,769X, April 3, 1817. 

Childs, Horace. U.S. Patent No. 4,693, August 12, 1846. 

210 Covered Bridges and the Birth of American Engineering 
Haupt, Herman. U.S. Patent No. 1,445, December 27, 1839.

Howe, William. U.S. Patent No. 1,711, August 3, 1840. 

______ . U.S. Patent No. 4,726, August 28, 1846. 

Long, S. H. U.S. Patent No. 5,862X, March 6, 1830. 

______ . U.S. Patent No. 1,397, March 6, 1830. 

______ . U.S. Patent No. 1,398, November 7, 1839. 

______ . U.S. Patent No. 5,366, November 13, 1847. 

Partridge, Reuben L. U.S. Patent No. 127,791, June 11, 1872. 

Post, Andrew J. U.S. Patent No. 81,817, September 1, 1868. 

Post, S. S. U.S. Patent No. 38,910, June 16, 1863. 

Pratt, Caleb, and Thomas W. Pratt. U.S. Patent No. 3,523, April 4, 1844. 

Sherman, Everett. U.S. Patent No. 191,522, June 5, 1877. 

Smith, Robert W. U.S. Patent No. 66,900, July 16, 1867. 

______ . U.S. Patent No. 97,714, December 7, 1869. 

Town, Ithiel. U.S. Patent No. 3,169X, January 28, 1820. 

Wheeler, Isaac H. U.S. Patent No. 107,576, September 20, 1870. 

Web Sites 

“Covered Bridge Preservation: National Best Practices Conference,” June 5–7, 2003.

 http://www.uvm.edu/coveredbridges/conference/2003.html. 

Covered Spans of Yesteryear Project. http://www.lostbridges.org. 

Historic American Buildings Survey / Historic American Engineering Record /

Historic American Landscapes Survey, Prints and Photographs Division, Library of Congress.

 http://www.loc.gov/pictures/collection/hh/. 

Federal Highway Administration, National Historic Covered Bridge Preservation Program.

 http://www.fhwa.dot.gov/bridge/covered.cfm. 

“Second National Covered Bridge Conference,” June 5–8, 2013.

http://www.woodcenter.org /2013-national-covered-bridge-conference/papers.cfm. 

World Guide to Covered Bridges database. http://www.woodcenter.org/CoveredBridges/. 

Covered Bridge Societies 

Bucks County Covered Bridge Society. http://www.buckscountycbs.org/.
 

Covered Bridge Society of Oregon. http://www.covered-bridges.org.
 

Indiana Covered Bridge Society. http://www.indianacrossings.org/.
 

National Society for the Preservation of Covered Bridges. http://www.coveredbridgesociety.org/.
 

New York State Covered Bridge Society. http://www.nycoveredbridges.org/.
 

Ohio Historic Bridge Association. http://oldohiobridges.com/ohba/.
 

The Theodore Burr Covered Bridge Society of Pennsylvania. http://www.tbcbspa.com/.
 

Vermont Covered Bridge Society. http://www.vermontbridges.com/index.htm.
 

Selected Bibliography 211 

 

Author Biographies
 

James Barker is president of J. A. Barker Engineering, Inc., a structural engineering firm that

specializes in the rehabilitation of historic bridges. He and his firm have designed significant repairs 

and rehabilitations for about forty-five historic bridges and barns, with twenty of those projects being 

timber-truss bridges. He is a registered professional engineer in Indiana, Kentucky, and New Hampshire. 

Lola Bennett is a bridge historian with a master’s degree in historic preservation. She has conducted

research on covered bridges across the United States since 2002. Her recent work with HAER’s 

National Covered Bridges Recording Project has included writing a comprehensive National

Historic Landmark Context Study and preparing National Historic Landmark nominations for 

selected covered bridges. 

Justine Christianson has been a historian with the Historic American Engineering Record

since 2001 and has worked on a variety of projects, including documentation of an oyster mill 

in Maryland and the Henry Hudson Parkway in New York City. In addition, she has prepared 

hundreds of projects for transmittal to the Library of Congress and authored the current HAER 

Guidelines for Historical Reports. She holds a master’s degree in history with a concentration in 

historic preservation from the George Washington University. 

Joseph Conwill, photographer and historian, has documented over twelve hundred covered bridges

since 1966, many of which no longer exist. He is the author of five books and the editor of Covered 

Bridge Topics, the quarterly magazine of the National Society for the Preservation of Covered 

Bridges. His photography of religious architecture is in the collections of several museums. He is a 

graduate of Northwestern University, where he majored in American studies. 

Sheila Rimal Duwadi is the Hazard Mitigation Team Leader at the Federal Highway Administration

(FHWA). As such she is responsible for research and development of bridge technologies and

methodologies for all extreme events. She also manages wood research and the National Historic 

Covered Bridge Preservation Research and Development Program. She represents the FHWA on 

a number of White House National Science and Technology Council subcommittees and is active 

within the engineering profession, currently the past chair of the Structural Engineering Institute’s 

Technical Administrative Division Executive Committee. She is a registered professional engineer 

in Virginia. 

Author Biographies 213 
Dario Gasparini is a professor of civil engineering at Case Western Reserve University. He

has published on the history of structural engineering with a particular focus on prestressing

technologies. He has authored and presented papers at several international conferences and has 

conducted numerous engineering studies for the Historic American Engineering Record since

1996. Chair of the History and Heritage Committee of the Cleveland Section of the American 

Society of Civil Engineers (ASCE), he is a corresponding member of the national ASCE History 

and Heritage Committee. 

Michael R. Harrison is the Robyn and John Davis Chief Curator of the Nantucket Historical 

Association. He has held curatorial positions at the National Building Museum, the Smithsonian’s 

National Museum of American History, and the Glasgow Museum of Transport, and is the author of

nearly seventy historical reports for HABS, HAER, and HALS. He is a graduate of the University of

Pennsylvania and holds a master’s degree in museum studies from the George Washington University.

Christopher H. Marston has been an architect with the Historic American Engineering Record

since 1989, serving as the project leader of the HAER National Covered Bridge Recording

Project since 2002. He was co-editor of the award-winning America’s National Park Roads

and Parkways: Drawings from the Historic American Engineering Record. He has presented on

HAER work at a variety of national conferences and is an active member of several preservation

organizations, including the Society for Industrial Archeology, Preserving the Historic Road,

Transportation Research Board ADC50 Committee, and Rustic Roads Advisory Committee in

Montgomery County, Maryland. He has degrees in architecture from the University of Virginia

and Carnegie-Mellon University. 

Richard O’Connor is division chief of the National Park Service’s Heritage Documentation

Programs (HABS, HAER, and HALS) and acting chief of the Historic American Engineering 

Record. He earned his Ph.D. at the University of Pittsburgh and has taught at several colleges and 

universities. Prior to assuming his current positions at the NPS, he served as a historian for the 

HAER program, preparing historical studies on a wide variety of historic industrial sites, including 

glass manufacturing, brick making, iron-pipe founding, and waterworks. His current interests 

involve the history and restoration of historic wood- and metal-working machinery. 

Matthew Reckard is a licensed engineer with an MS in historic preservation, working in the 

Anchorage, Alaska, area. He has performed historical research, condition evaluation, structural 

analysis, plan preparation, and project management for repair and rehabilitation of many covered 

bridges and other historic structures. His early career was spent in engineering research at Brookhaven

National Laboratory and the Alaska Department of Transportation and Public Facilities. He now 

divides his time between consulting engineering, managing an Alaskan hot springs resort, and 

professional piano playing. 

Rachel Herring Sangree is the director of undergraduate studies and a lecturer in the Department

of Civil Engineering at the Johns Hopkins University. A professional engineer in Maryland, she 

has degrees in civil engineering from Bucknell University and the Johns Hopkins University, where 

she earned her Ph.D. In addition to historic structures, she is interested in improving the quality 

214 Covered Bridges and the Birth of American Engineering 
of undergraduate engineering education as well as exploring methods to attract and retain future 

generations of civil engineers. She was principal investigator for the HAER engineering study of 

the reconstruction of the Gilpin’s Falls Covered Bridge in Cecil County, Maryland. 

David A. Simmons is senior editor of Timeline, a popular history journal published by the Ohio 

Historical Society (now the Ohio History Connection). Previously, he directed the process for 

listing properties in the National Register of Historic Places in the Ohio State Historic Preservation 

Office. The recipient of several writing awards for excellence in industrial archaeology, he currently 

serves as president of the Ohio Historic Bridge Association. He holds undergraduate and graduate 

degrees from Miami University in Oxford, Ohio. 

Author Biographies 215 

Appendix Covered Bridges in the HABS/HAER Collection 217

Appendix

Covered Bridges in the 

HABS/HAER Collection

HABS/HAER 

Number Name Location Truss Type World Guide No. Date

Alabama

HAER AL-201 Swann Bridge

(Joy Bridge)

Cleveland vicinity,

Blount County

Town

lattice 01-05-05 1933

HAER AL-203 Horton Mill Bridge Oneonta vicinity,

Blount County

Town

lattice 01-05-07 1934

HABS AL-361 Cripple Deer Creek 

Covered Bridge

Allsboro vicinity, 

Colbert County

Town

lattice 01-17-02x ca. 1820 (HH); 

1859 (WG)

HABS AL-361-A Big Bear Creek 

Covered Bridge

Allsboro vicinity, 

Colbert County

Town

lattice 01-17-03x Unknown

HABS AL-361-B Buzzard Roost

Covered Bridge

Cherokee vicinity,

Colbert County

Town

lattice 01-17-01x ca. 1866

HABS AL-445 Covered Bridge Eastaboga,

Talladega County

Town lattice,

Kingpost 01-61-06x pre-1861

Arkansas

HAER AR-42 Fourteenth Street Bridge North Little Rock, 

Pulaski County

Kingpost

uncovered 01-17-01x ca. 1925

California

HABS CA-1401 [Bridgeport]

Covered Bridge

Bridgeport,

Nevada County Howe 05-29-01 1862

HAER CA-41† Bridgeport

Covered Bridge

Bridgeport,

Nevada County Howe 05-29-01 1862

HABS CA-158 [Knight’s Ferry]

Covered Bridge

Knights Ferry,

Stanislaus County Howe 05-50-01 1863

HAER CA-314† Knight’s

Ferry Bridge

Knights Ferry,

Stanislaus County Howe 05-50-01 1863

HAER CA-106† Wawona

Covered Bridge

Wawona,

Mariposa County Queenpost 05-22-01 1868; rebuilt 1956

HAER CA-312† Honey Run Bridge

(Carr Hill Bridge)

Paradise vicinity,

Butte County Pratt 05-04-01 ca. 1886 (HH); 

1896 (WG)

HAER CA-313 Powder Works Bridge 

(Paradise Park Bridge)

Paradise Park,

Santa Cruz County Smith (4) 05-44-03 1872

HABS CA-1551 [Glen Canyon] 

Covered Bridge

Glen Canyon, 

Santa Cruz County Howe 05-44-01x 1892
218 Covered Bridges and the Birth of American Engineering

HABS/HAER 

Number Name Location Truss Type World Guide No. Date

Colorado

HAER CO-49 Hortense Bridge Nathrop, Chaffee 

County

Queenpost 

uncovered 06-09-u03x 1880

Delaware

HABS DE-162 Ashland

Covered Bridge

Ashland,

New Castle County

Town

lattice 08-02-02 mid-1800s

HABS DE-1† Smith’s

Covered Bridge

Granogue vicinity,

New Castle County Burr 08-02-01x 1839

Georgia

HAER GA-138

Red Oak Creek Bridge 

(Imlac or Big Red Oak 

Creek Bridge)

Woodbury vicinity,

Meriwether County

Town

lattice 10-99-02 ca. 1840

HAER GA-140

Watson Mill Bridge 

(Broad River Bridge) 

[Carlton Bridge]

Comer vicinity, 

Madison County

Town

lattice 10-97-01 1885

HABS GA-185 [Papermill Road or Sope 

Creek] Covered Bridge

Atlanta vicinity,

Cobb County

Town

lattice 10-33-01x 1886

Illinois

HABS IL-243† Eames Covered Bridge 

[Allman Bridge]

Oquawka vicinity,

Henderson County Burr 13-36-01#2 1865

HABS IL-25-19† Wooden Covered Bridge

[Homer Park Bridge]

Homer vicinity, 

Champaign County Howe 13-10-02x 1865

HABS IL-242† Jack’s Mill

Covered Bridge

Oquawka vicinity,

Henderson County

Town

lattice 13-36-02#2x 1845

HABS IL-1002

[Rock Island Railroad] 

Bridge Spanning 

Mississippi River

Rock Island, Rock 

Island County

Howe

uncovered 13-81-u01x 1853 (WG)

Indiana

HABS IN-24-20†

Whitewater

Canal Aqueduct 

(Metamora Aqueduct)

Metamora, 

Franklin County Burr 14-24-11 1846 

HAER IN-108†

Duck Creek Aqueduct

(Whitewater Canal or 

Metamora Aqueduct)

Metamora, 

Franklin County Burr 14-24-11 1846

HAER IN-28†

Deer’s Mill

Covered Bridge 

[Bluff Mills Bridge]

Alamo vicinity,

Montgomery County Burr 14-54-03 1878

HAER IN-29† Adams Mill Bridge Cutler,

Carroll County Howe 14-08-01 1871

HAER IN-30† Vermont

Covered Bridge

Kokomo,

Howard County Smith (3) 14-34-01 1875; moved 1958

HAER IN-33† Busching

Covered Bridge

Versailles,

Ripley County Howe 14-69-04 1885

HAER IN-40 Leatherwood Station

Covered Bridge

Montezuma,

Parke County Burr 14-61-25 1899;

moved 1981

HAER IN-44† Mansfield Covered Bridge Mansfield,

Parke County

Burr 14-61-20 1867
Appendix Covered Bridges in the HABS/HAER Collection 219

HABS/HAER 

Number Name Location Truss Type World Guide No.

HAER IN-45† Medora Bridge 

[Dark Bridge]

Medora, 

Jackson County Burr 14-36-04 1875

HAER IN-48†

Jackson Covered Bridge 

[Rockport Wright’s 

Mill Bridge]

Bloomingdale vicinity, 

Parke County Burr 14-61-28 1861

HAER IN-49† Narrows Bridge

[Lusk Mill Bridge]

Turkey Run State Park, 

Parke County Burr 14-61-36 1882

HAER IN-50† Cumberland Covered

Bridge [Matthews Bridge]

Matthews,

Grant County Howe 14-27-01 1879

HAER IN-57† Ceylon Covered Bridge Geneva, Adams County Howe 14-01-02 ca. 1860 

HAER IN-103†* Pine Bluff Bridge Bainbridge vicinity, 

Putnam County Howe 14-67-03 1886

HAER IN-104* Cataract Falls Bridge Cataract, Owen 

County Smith (3) 14-60-01 1876

HAER IN-105† West Union Bridge West Union, 

Parke County Burr 14-61-27 1876

HAER IN-106† Forsythe Bridge 

[Forsythe Mill Bridge]

Moscow vicinity,

Rush County Burr 14-70-04 1888

HABS IN-24-1†

Kennedy Bridge

[East Hill, East 2nd Street, 

or Cemetery Bridge]

Rushville vicinity, 

Rush County Burr 14-70-10x 1881

HAER IN-27† Brownsville Covered

Bridge (Wagon Bridge)

Brownsville,

Union County Long 14-81-01x 1840;moved 1974

HAER IN-31† Dunlapsville

Covered Bridge

Dunlapsville,

Union County Burr 14-81-02x 1870

HAER IN-39 Gosport Covered Bridge Gosport, Owen County Smith 14-60-03x 1870

HAER IN-46† Bells Ford Bridge Seymour,

Jackson County Post 14-36-03x

1869; collapsed 

and salvaged 

2006

Iowa

HAER IA-64 Holliwell Bridge Winterset vicinity,

Madison County

Town

lattice 15-61-05 1880

HAER IA-92 Cutler Bridge 

(Donahoe Bridge)

Winterset vicinity,

Madison County

Town

lattice 15-61-02 1871; 

moved 1971

HAER IA-93 Hogback

Bridge

Winterset vicinity,

Madison County

Town

lattice 15-61-04 1884

HAER IA-94†

Imes Bridge 

(Wilkins Mill Bridge) 

[King or Munger Bridge]

St. Charles,

Madison County

Town

lattice 15-61-06 1870;

moved 1977

HAER IA-95† Roseman Bridge

(Oak Grove Bridge)

Winterset vicinity,

Madison County

Town

lattice 15-61-07 1883

HABS IA-30-2† [Owens]

Covered Bridge

Carlisle vicinity,

Warren County Howe 15-77-01

1866 (WG);

1882 (HH);

1888 (R. S. Allen);

moved 1968

HAER IA-76† Red Bridge [Yellow River 

or Oelberg Bridge]

Postville,

Allamakee County 

Pratt

uncovered 15-03-u02 1920

Date
220 Covered Bridges and the Birth of American Engineering

HABS/HAER 

Number Name Location Truss Type World Guide No.

Kansas

HABS KS-13 [Springdale]

Covered Bridge

Springdale vicinity, 

Leavenworth County Howe 16-52-01x 1859

Kentucky

HAER KY-49 Bennett’s Mill Bridge Lynn vicinity,

Greenup County Wheeler 17-45-01x 1875;

rebuilt 2004

HABS KY-20-11† [Butler]

Covered Bridge

Butler,

Pendleton County Burr 17-96-02x 1870

HABS KY-20-20† [Cynthiana]

Covered Bridge

Cynthiana,

Harrison County Burr 17-49-05x 1807 (HH);

1837 (WG)

Maine

HAER ME-3

New Portland 

Suspension Bridge

(Wire Bridge)

New Portland, 

Somerset County Suspension 19-13-S1 ca. 1866

HAER ME-4 Lovejoy Bridge

[South Andover Bridge]

Andover,

Oxford County Paddleford 19-09-01 1867

HAER ME-69† Sunday River Bridge 

(Artist’s Bridge)

Newry vicinity,

Oxford County Paddleford 19-09-04 1872

HABS ME-61† [Babb’s]

Covered Bridge

South Windham 

vicinity,

Cumberland County

Queenpost 19-03-01x 1840 (HH);

1864 (WG)

HAER ME-51

Meeting House Bridge 

(Sinnott Road Railroad 

Bridge) (spanning Boston 

& Maine Railroad) 

Arundel, 

York County

Howe,

boxed pony 19-16-P02x 1908 (HH);

ca. 1905 (WG)

Maryland

HABS MD-12† [Jericho]

Covered Bridge

Jerusalem vicinity,

Baltimore County Burr 20-03-02 1865

HAER MD-187 Jericho

Covered Bridge

Jerusalem vicinity,

Baltimore County Burr 20-03-02 1865

HAER MD-174†* Gilpin’s Falls

Covered Bridge

North East, 

Cecil County Burr 20-07-01 1860

Massachusetts

HAER MA-83

Hastings Bridge

(spanning Boston & 

Maine Railroad)

Sterling,

Worcester County

Howe,

boxed pony 21-14-P01 1892

HABS MA-101† [Railroad Combination]

Covered Bridge 

Montague City,

Franklin County

Howe with arch 

(through & deck) 21-06-31#3x 1870

HABS MA-225† Nehemiah Jewett’s Bridge 

[Pepperell #1 Bridge]

Pepperell,

Middlesex County

Town

lattice 21-09-01x 1847

HABS MA-440 [Bannigor Heights or Red]

Covered Bridge

Millville,

Worcester County Howe 21-14-49x ca. 1888

HABS MA-497 [Collins Station]

Covered Bridge

Ludlow-Wilbraham,

Hampden County Howe 21-07-17x 1851

HAER MA-94 Boston & Maine Railroad, 

Clark Street Bridge

Belmont,

Middlesex County

Howe,

boxed pony 21-09-P02x 1908

HAER MA-116 Boston & Maine Railroad,

Essex Street Bridge

Swampscott,

Essex County

Howe,

boxed pony 21-05-P02x 1901

Date
Appendix Covered Bridges in the HABS/HAER Collection 221

HABS/HAER 

Number Name Location Truss Type World Guide No.

Michigan

HAER MI-331 White’s Bridge Smyrna, 

Ionia County Brown 22-34-01x 1869

Minnesota

HAER MN-123† Zumbrota Bridge Zumbrota,

Goodhue County

Modified

lattice 23-25-01 1869; moved 1997

Mississippi

HABS MS-90 Old Covered Bridge Steens vicinity,

Lowndes County

Town

lattice 24-44-02x Unknown

Missouri

HABS MO-270† Noah’s Ark

Covered Bridge

Hoover vicinity,

Platte County

Modified

Howe 25-83-01x 1878;

moved 1965

HABS MO-1156

Sandy Creek Bridge 

[LeMay Ferry Road 

Bridge]

Goldman vicinity,

Jefferson County Howe 25-50-01#2 1887

HABS MO-1307

Bollinger Covered Bridge 

& Mill [Bollinger 

Mill Bridge]

Bufordville, Cape 

Girardeau County Howe 25-16-01 1868

HABS MO-1325 [Allenville]

Covered Bridge

Allenville,Cape

Girardeau County

Multiple

kingpost 25-16-02x 1870

New Hampshire

HAER NH-8†* Cornish-Windsor Covered

Bridge (Cornish Bridge)

Cornish, 

Sullivan County

Town

lattice 29-10-09#2 1866

HAER NH-33†*

Bath-Haverhill Bridge

(Haverhill-Bath Bridge)

[Woodsville Bridge]

Woodsville,

Grafton County

Town

lattice 29-05-04 1829

HAER NH-34 Bath Bridge Bath,

Grafton County

Multiple

kingpost 29-05-03 1832

HAER NH-35 Wright’s Bridge

[Wright Railroad Bridge]

Claremont vicinity,

Sullivan County

Double Town

lattice with arch 29-10-04#2 1906

HAER NH-36†* Sulphite Railroad Bridge Franklin,

Merrimack County

Pratt

deck 29-07-09 1896

HAER NH-38†*

Contoocook Railroad

Bridge (Hopkinton

Railroad Bridge)

Hopkinton,

Merrimack County

Town

lattice 29-07-07#2 1889

HAER NH-39 Clark’s Bridge [Pinsley 

Railroad Bridge]

Lincoln,

Grafton County Howe 29-05-14 1904;

moved 1965

HAER NH-40 Kenyon Bridge 

(Blacksmith Shop Bridge)

Cornish, 

Sullivan County

Multiple

kingpost 29-10-01 1882

HAER NH-41 Honeymoon Bridge

(Jackson Bridge)

Jackson,

Carroll County

Paddleford

with arch 29-02-01 1876

HAER NH-42 Hancock-Greenfield

Bridge (County Bridge)

Greenfield,

Hillsborough County Teco 29-06-02#2 1937

HAER NH-43

Livermore Bridge [Blood 

Brook or Old Russell 

Hill Road Bridge]

Wilton,

Hillsborough County

Town,

boxed pony 29-06-P1 ca. 1937

Date
222 Covered Bridges and the Birth of American Engineering

HABS/HAER 

Number Name Location Truss Type World Guide No.

HAER NH-44

Rollins Farm Bridge 

(Boston and

Maine Railroad,

Western Route, 

Portland Division, 

Bridge No. 69.19)

Rollinsford, 

Strafford County

Howe,

boxed pony 29-09-P1 1904 (WG);

rebuilt 1929 (HH)

HAER NH-45 Mechanic Street

(Israel River Bridge)

Lancaster,

Coos County Paddleford 29-04-06 1862

HAER NH-48†

Boston & Maine Railroad, 

Berlin Branch Bridge 

#148.81 (Moose Brook 

Bridge) [Boston & Maine 

Railroad #262 Bridge]

Gorham, Coos County Howe, boxed 

pony

29-04-P1x/

29-04-p1#

1918; rebuilt 

2012-2016

HAER NH-49 Railroad, Berlin Branch 

#143.06 (Snyder Brook 

Boston & Maine 

Bridge)

Randolph,

Coos County

Howe,

boxed pony 29-04-P2 1918

HAER NH-50† Whittier Bridge

(Bearcamp Bridge)

West Ossipee,

Carroll County Paddleford 29-02-08 1871

HABS NH-21† Contoocook

Covered Bridge

Hopkinton,

Merrimack County Long 29-07-63x 1853

HABS NH-29† [Fairlee-Orford]

Covered Bridge

Orford, 

Grafton County

Town

lattice 29-05-94x ca. 1850 (HH); 

1856 (WG)

HABS NH-30† [Henniker Road]

Covered Bridge

Hopkinton vicinity,

Merrimack County

Town lattice

with arch 29-07-62x 1863

New Jersey

HABS NJ-442†

[Green Sergeants

or Sergeantsville] 

Covered Bridge

Sergeantsville vicinity,

Hunterdon County Queenpost 30-10-01 1872

HABS NJ-654† Old Covered Bridge 

& Flood Gates

South Pemberton, 

Burlington County Stringer Unknown

New York

HABS NY-4-204† Perrine’s Bridge Rifton, Ulster County Burr 32-56-01 1850 (HH);

1844 (WG)

HABS NY-263 Hyde Hall, Covered 

Bridge

East Springfield, 

Otsego County Burr 32-39-01 ca. 1825

HAER NY-330 Hyde Hall Bridge East Springfield, 

Otsego County Burr 32-39-01 ca. 1825

HAER NY-170† Jay Covered Bridge Jay, Essex County Howe 32-16-01 1857

HAER NY-329 Beaverkill Bridge

(Conklin Bridge)

Roscoe vicinity, 

Sullivan County

Town

lattice 32-53-02 1865

HAER NY-332† Powerscourt Bridge

(Percy Bridge)

Huntingdon County, 

Quebec Province, 

Canada

McCallum 61-27-01 1861

HABS NY-359† Blenheim Covered Bridge North Blenheim,

Schoharie County

Long with arch, 

double barrel 32-48-01x 1855

HAER NY-331 Blenheim Bridge North Blenheim,

Schoharie County

Long with arch, 

double barrel 32-48-01x 1855

North Carolina

Date
Appendix Covered Bridges in the HABS/HAER Collection 223

HABS/HAER 

Number Name Location Truss Type World Guide No.

HAER NC-46† Bunker Hill Bridge Claremont vicinity,

Catawba County Haupt 33-18-01 1895

Ohio

HABS OH-22-12† [Spain Creek]

Covered Bridge

North Lewisburg 

vicinity,

Union County

Partridge 35-80-02 ca. 1859 (HH); 

ca. 1870 (WG)

HABS OH-2229 Roberts Bridge Eaton vicinity,

Preble County Burr 35-68-05 1829;

moved 1990

HAER OH-45† John Bright No. 2 

Covered Bridge

Carroll vicinity,

Fairfield County

Bowstring, iron

suspension truss 35-23-10

1881;

moved 1988

HAER OH-87† Germantown

Covered Bridge

Germantown,

Montgomery County

Bowstring, iron

suspension truss 35-57-01 1865;

moved 1911

HAER OH-122†* Eldean Bridge 

(Allen’s Mill Bridge)

Troy vicinity,

Miami County Long 35-55-01 1860

HAER OH-123

Crum Bridge (Knowlton 

Bridge) (Long Bridge)

(Old Camp Bridge)

Rinard Mills vicinity, 

Monroe County

Multiple

kingpost with

tied arch

35-56-18 1867 

HAER OH-125†

Pottersburg Bridge

(Upper Darby Bridge) 

(Beltz Mill Bridge)

North Lewisburg 

vicinity,

Union County

Partridge 35-80-01 1872;

moved 2006

HAER OH-126†* Harshman Bridge

(Four Mile Bridge)

Fairhaven vicinity,

Preble County Childs 35-68-03 1894

HAER OH-127 Salt Creek Bridge 

(Johnson Mill Bridge)

Norwich vicinity, 

Muskingum County Smith (2) 35-60-31 1876

HAER OH-130* Rinard Bridge Wingett Run vicinity, 

Washington County Smith (3) 35-84-28_2 1876

HAER OH-138 Strength of Burr 

Arch-Trusses

Cleveland,

Cuyahoga County Burr

HABS OH-45 Old Covered Bridge 

(Clay Pike Bridge)

Zanesville vicinity,

Muskingum County

Multiple

kingpost 35-60-49 1878

HABS OH-22-13† [London Road or Reed] 

Covered Bridge

North Lewisburg 

vicinity,

Union County

Partridge 35-80-05x 1884

HABS OH-44 Old Covered Bridge 

[Pleasant Valley Bridge]

Hopewell vicinity,

Muskingum County Smith (3) 35-60-30x 1875

HABS OH-270† [West] Covered Bridge Newton Falls,

Trumbull County

Howe,

double barrel 35-78-03x 1856 (WG)

HABS OH-623† Covered Bridge Collinsville vicinity,

Butler County Smith (4) 35-09-11x 1869

HABS OH-624†

New London Pike

Covered Bridge 

(Hogan’s Bridge)

Hamilton vicinity,

Butler County Burr 35-09-01x Unknown

HABS OH-2224 [Clarksville]

Covered Bridge

Clarksville,

Clinton County Burr 35-14-01x ca. 1870

Oregon

HAER OR-26 Grave Creek Bridge 

[Sunny Valley Bridge]

Sunny Valley, 

Josephine County Howe 37-17-01 1920

HAER OR-119 Pengra Bridge

(Fall Creek Bridge)

Jasper vicinity,

Lane County Howe 37-20-15#2 1938

Date
224 Covered Bridges and the Birth of American Engineering

HABS/HAER 

Number Name Location Truss Type World Guide No.

HAER OR-120 Short Bridge 

[Cascadia Bridge]

Cascadia vicinity,

Linn County Howe 37-22-09#2 1945

HAER OR-123 Gallon House Bridge Silverton,

Marion County Howe 37-24-01 1916

HAER OR-124† Larwood Bridge Lacomb vicinity, 

Linn County Howe 37-22-06#2 1941 (HH);

1939 (WG)

HAER OR-125 Office Bridge

(Westfir Covered Bridge)

Westfir,

Lane County Howe 37-20-39 1944

HAER OR-126† Neal Lane Bridge Myrtle Creek,

Douglas County Kingpost 37-10-07 1939 (HH);

1929 (WG)

HAER OR-136 Goodpasture Bridge

(McKenzie River Bridge)

Vida,

Lane County Howe 37-20-10 1938

HAER OR-145

Fisher School

Covered Bridge 

(Five Rivers Bridge)

Fisher vicinity,

Lincoln County Howe 37-21-11 1919

HAER OR-8 Jordan Covered Bridge 

(Thomas Y Bridge)

Scio vicinity,

Linn County Howe 37-22-01x 1937

HAER OR-15 Horse Creek 

Covered Bridge

McKenzie Bridge 

vicinity, Lane County Howe 37-20-12x 1930

Pennsylvania

HABS PA-19†

[Thomas Mill, 

Spruce Mill, or Megargee 

Mansion] Covered Bridge

Philadelphia,

Philadelphia County Howe 38-51-01 1855

HABS PA-415† Bells Mill Bridge 

[Sewickley Bridge]

West Newton vicinity, 

Westmoreland County Burr 38-65-01 1850

HABS PA-535† Waterford Covered Bridge

[Wattsburg Road Bridge]

Waterford,

Erie County

Town

lattice 38-25-04 1880s (HH);

ca. 1875 (WG)

HABS PA-1020 Griesemer Mill

Covered Bridge

Yellow House vicinity,

Berks County Burr 38-06-03 1832 (HH);

1868 (WG)

HABS PA-1108

Bartram’s Covered Bridge 

[William Sager’s

Gristmill Bridge]

[Lewis Garrett’s Bridge]

Newton Square 

vicinity,

Chester County

Burr 38-15-17 1860

HAER PA-67

Gross Covered Bridge 

(Klinepeter’s Bridge)

(Beaver Springs Bridge) 

[Overflow Bridge]

Beaver Springs vicinity,

Snyder County Burr 38-55-03 ca. 1878 (HH);

1871 (WG)

HAER PA-197 Cabin Run

Covered Bridge

Pipersville,

Bucks County

Town

lattice 38-09-10 1874

HAER PA-198 Loux Covered Bridge 

[Loux Mill Ford Bridge]

Pipersville, Bucks 

County

Town

lattice 38-09-11 1874

HAER PA-350 Felten’s Mill

Covered Bridge 

Breezewood vicinity,

Bedford County Burr 38-05-03 1892

HAER PA-352

Jackson’s Mill

Covered Bridge 

[Barnhart’s Bridge]

Breezewood vicinity,

Bedford County Burr 38-05-25 1889

HAER PA-361

Raystown Covered Bridge 

(Diehl’s Bridge) (Turner’s

Bridge) [Williams Bridge]

Manns Choice vicinity,

Bedford County Burr 38-05-19 1892

HAER PA-458† McConnell’s Mill Bridge Ellwood City vicinity,

Lawrence County Howe 38-37-01 1875

Date
Appendix Covered Bridges in the HABS/HAER Collection 225

HABS/HAER 

Number Name Location Truss Type World Guide No.

HAER PA-491†

Pleasantville

Covered Bridge 

(Manatawny Bridge)

Manatawny vicinity, 

Berks County

Burr archstiffened pony 38-06-01 1852; 1856

HAER PA-586†*

Pine Grove Bridge 

[Little Britain or Pine 

Grove Forge Bridge]

Oxford vicinity, 

Chester County Burr 38-15-22#3 1884

HAER PA-587 Dreibelbis Station Bridge Lenhartsville vicinity,

Berks County Burr 38-06-07 1869

HAER PA-588 Uhlerstown Bridge

[Lock 18 Canal Bridge]

Uhlerstown, 

Bucks County

Town

lattice 38-09-08 1856 (HH);

1830 (WG)

HAER PA-622* Kidd’s Mill Bridge Greenville vicinity,

Mercer County Smith (2) 38-43-01 1868

HAER PA-623

Mean’s Ford Bridge 

Park Bridge)

(Burnt Mill Bridge) 

(Ralph Stover State

Point Pleasant,

Bucks County

Howe

boxed pony 38-09-P1 ca. 1860s

HAER PA-624 Academia Bridge

(Pomeroy Bridge)

Academia,

Juniata County Burr 38-34-01 1902

HAER PA-638 King’s Bridge New Lexington, 

Somerset County Burr 38-56-06 1906

HAER PA-645* Structural Study

of Smith Trusses Smith

HABS PA-351 Snyder’s Fording 

Covered Bridge

Hunterstown vicinity,

Adams County Burr 38-01-04x 1868

HABS PA-618† [Grimes]

Covered Bridge

Ruff Creek vicinity, 

Greene County Kingpost 38-30-22x 1888

HABS PA-1173†

Johnson’s Mill Bridge 

[Henry Musselman’s 

Bridge]

Chickies,

Lancaster County Burr 38-36-35x 1866 (HH);

1854 (WG)

HABS PA-5184

Detters Mill Covered 

Bridge [Pickett’s or

Emig’s Mill Bridge]

Detters Mill, 

York County Burr 38-67-01x ca. 1815 (HH);

1848 (WG)

HAER PA-68 Kuhn’s Fording Bridge 

[Mummert’s Grove Bridge]

East Berlin vicinity,

Adams County Burr 38-01-12x 1862 (WG)

HAER PA-119

Philadephia & Reading 

Railroad, Walnut Street 

Bridge

Reading, Berks County Kingpost 

uncovered 38-06-u01x 1869 (WG)

South Carolina

HABS SC-391† Chapman’s Bridge Gowensville vicinity,

Pickens County

Multiple

kingpost 40-37-02x

1912 (HH);

1924 (WG);

moved 1969

HABS SC-396†

Lower Gassaway Bridge 

[Rice Bridge]

[Twelve Mile Creek]

Norris vicinity, 

Pickens County

Multiple

kingpost 40-39-02x ca. 1900 (HH);

1905 (WG)

Tennessee

HABS TN-224 Elizabethton

Covered Bridge

Elizabethton,

Carter County Howe 42-10-01 1884

HAER TN-41 Doe River Bridge 

(Elizabethton Bridge)

Elizabethton,

Carter County Howe 42-10-01 1884

Date
226 Covered Bridges and the Birth of American Engineering

HABS/HAER 

Number Name Location Truss Type World Guide No.

HAER TN-48 Nashville Toll Bridge 

(Abutments)

Nashville, 

Davidson County Modified Burr 42-19-02x 1823

HAER TN-31 Marlow Road Bridge Clinton,

Anderson County

Kingpost pony 

uncovered 42-01-u01x 1918

Virginia

HAER VA-1† Humpback

Covered Bridge

Covington vicinity,

Alleghany County

Multiple

kingpost 46-03-01 1857

HAER VA-126

Link Farm

Covered Bridge 

(Sinking Creek Bridge)

Newport vicinity, 

Giles County

Polygonal

arch 46-35-01 1916

HABS VA-11-13† (Trent’s) Covered Bridge 

[Hornquarter Bridge]

Cumberland vicinity,

Cumberland County

Town

lattice 46-25-01x 1844

HABS VA-567 Covered Bridge Lexington vicinity,

Rockbridge County Burr 46-78-02x 1877

HAER VA-20

Marysville

[Gladys Bridge]

Covered Bridge Gladys vicinity,

Campbell County Kingpost 46-16-01x 1878

Vermont

HAER VT-28†* Brown Bridge

[Hollow Bridge]

Shrewsbury,

Rutland County

Town

lattice 45-11-09 1880

HAER VT-29 Flint Bridge Tunbridge vicinity, 

Orange County Queenpost 45-09-11 1874

HAER VT-30†* Taftsville Bridge Taftsville,

Windsor County

Multiple

kingpost 45-14-12 1836

HAER VT-31 Pulp Mill Bridge 

(Paper Mill Bridge)

Weybridge,

Addison County Burr 45-01-04#2 1854

HAER VT-32† Shoreham Railroad Bridge 

[Rutland Railroad Bridge]

Shoreham,

Addison County Howe 45-01-05 1897

HAER VT-33†* Morgan Bridge 

(Upper Bridge)

Belvidere,

Lamoille County Queenpost 45-08-07 ca. 1886

HAER VT-34

Village Bridge

(Big Eddy Bridge) 

[Great Eddy Bridge]

Waitsfield,

Washington County Burr 45-12-14 1833

HAER VT-36 Swallow’s Bridge

(Best’s Bridge)

West Windsor, 

Windsor County Tied Arch 45-14-10 1890

HAER VT-37† Pine Brook Bridge 

(Wilder Bridge)

Waitsfield,

Washington County Kingpost 45-12-12 1872

HAER VT-40† Hall Bridge 

(Osgood Bridge)

Rockingham,

Windham County Town 45-13-07#2 1982

HAER VT-1-A†

E. & T. Fairbanks & 

Company, Two-Story 

Covered Bridge

St. Johnsbury,

Caledonia County

Town lattice

with arch 45-03-68x ca. 1876

Washington

HAER WA-133

Harpole Bridge

(Manning-Rye Bridge)

[Colfax Road Bridge]

Colfax vicinity,

Whitman County

Howe

boxed through 47-38-01 ca. 1922

HAER WA-28 Grays River

Covered Bridge

Grays River vicinity, 

Wahkiakum County Howe 47-35-01x 1905

Date
Appendix Covered Bridges in the HABS/HAER Collection 227

HABS/HAER 

Number Name Location Truss Type World Guide No.

West Virginia

HAER WV-8† Barrackville

Covered Bridge

Barrackville,

Marion County Burr 48-25-02 1853

HAER WV-31 Staats Mill

Covered Bridge

Ripley vicinity,

Jackson County Long 48-18-04 1887; moved 1983

HAER WV-32

Milton Covered Bridge 

(Sink’s Mill Bridge) 

(Mud River Bridge)

Milton,

Cabell County

Howe

with arch 48-06-01 1876; moved 

2001

HAER WV-53 White’s Creek Covered

Bridge Abutments

Cyrus vicinity,

Wayne County Howe 48-50-01x 1877

Wisconsin

HABS WI-28-12† [Cedarburg]

Covered Bridge

Cedarburg vicinity,

Ozaukee County

Town

lattice 49-46-01 1876

HAER WI-117† Cedarburg

Covered Bridge

Cedarburg,

Ozaukee County

Town

lattice 49-46-01 1876

HABS WI-13 Seventh Street Bridge Hudson,

St. Croix County

Howe pony 

uncovered 49-56-u01x 1910

Wyoming

HAER WY-60 New Fork River Bridge Boulder,

Sublette County

Kingpost pony 

uncovered 50-18-u01 1917

NOTES:

This list includes all historic wood truss bridges in the HABS/HAER Collection, 

covered and uncovered.

HABS/HAER documentation for each bridge in this list can be accessed through 

the Web site of the Prints and Photographs Division of the Library of Congress,

http://loc.gov/pictures/collection/hh/.

Bridge names in parentheses are alternatives noted by HABS/HAER. 

Bridge names in square brackets are alternatives noted in the World Guide 

to Covered Bridges.

† Documentation includes drawings.

* Documentation includes engineering analysis.

1

 An “x” following a World Guide number denotes a bridge that is no longer extant.

(HH) Date of construction is from HABS/HAER report.

(WG) Date of construction is from World Guide.

Date

Index 229

Index

Note: Bolded page number indicates illustration

Academia Bridge: 96

Allen, Richard Sanders (1917–2008): 189

Andrews, Tim (b. 1959): 45, 177-78, 177, 199

arson/fire: 

bridges destroyed by arson: 23, 31, 45

49, 64

bridges damaged or destroyed in fires:

28, 54, 56, 169

arson statistics: 74 (n. 58)

fire-resistant technologies: 40, 198

Ashtabula Bridge: 64, 88

Ballard, Ephraim (1725¬–1812): 166 

Barrackville Bridge: 11, 168, 169

Bartonsville Covered Bridge: 46, 187

Bath-Haverhill Bridge: 13, 165, 180-81 (n. 15, 20) 

Beaverkill Bridge: 13, 96

Bedell Bridge: 63

Bell’s Ford Bridge: 26

Bennett’s Mill Bridge: 29

Biddle, Owen (1774–1806): 53, 103

Blenheim Bridge: 17, 41, 42, 173, 187

Blair Bridge: 44, 60

Boody, Azariah: 61, 138

Bouscaren, Louis: 87-88

Buonopane, Stephen: 107, 151-52

bridge companies

American Bridge Company: 62, 146, 175

Boody, Stone, and Company: 61, 138

Columbia Bridge Works: 29

Hoffman and Bates: 168

Pacific Bridge Company: 25, 149, 170

Smith Bridge Company: 65,66, 145,

147, 170, 174-75

Stone and Boomer: 168

Toledo Bridge Company: 65, 146, 175 

Bridgeport Bridge: 18, 182 (n. 39) 

Burr, Theodore (1771–1822): 56, 104-5, 119-21, 

163, 179 (n. 6)

Brown Bridge: 36, 58, 110, 165, 174

Brown, Josiah: 28

Brushy Fork Bridge: 150

Bunker Hill Bridge: 26, 128

Callahan, William F. (1891–1964): 196

Cataract Bridge: 146, 148, 152

Cedarburg Covered Bridge: 43

Chaley, Joseph: 136

Chapin, Solon (1803–72): 163 

Chenoweth, Lemuel (b. 1811): 11, 168-69

Childs, Horace (1807–1900): 27, 59, 133

Clark’s Railroad Bridge: 21

Clough, Philip and Betsy: 189

Colossus; also Upper Ferry Bridge, Fairmount

Bridge: 54, 105, 119, 121

Connecticut River Bridge (Western Railroad): 60, 138

Contoocook Railroad Bridge: 16, 127, 192-93, 193

Cooper, Theodore (1839–1919): 88, 126
230 Covered Bridges and the Birth of American Engineering

Cornish-Windsor Bridge: 15, 102, 128, 192

covered bridge associations

Indiana Historical Society, Covered

Timber Bridge Committee: 194

National Society for the Preservation of

Covered Bridges: 33, 37, 45, 189, 190-93

New Hampshire Covered Bridge

Association: 194

Ohio Historic Bridge Association; also

Southern Ohio Covered Bridge

Association: 195-96, 196

Parke County Incorporated: 195

Culmann, Carl (1821–81): 125, 134, 135, 141

Daniels, J. J. (Joseph John) (1826–1916): 12, 59, 90, 123,

167, 169; Stephen (father): 59

Davidson, John: 13, 166

Delafield, Capt. Richard (1798–1873): 64

DeLony, Eric N.: iii, 1, 37

Doe River Bridge: 19

Dover Toll Bridge: 94

Dreibelbis Station Bridge: 63, 160, 165

Du Bois, Augustus Jay (1849–1915): 98-99

Duck Creek Aqueduct; also Whitewater Canal

Aquaduct, Metamora Aqueduct: 11, 35, 36

Dufour, Guillaume Henri (1787–1875): 85, 86

Dunlap’s Creek Bridge: 64

Edna Collins Bridge: 72 (n. 25)

Eldean Bridge: 18, 59, 60, 131, 165

Ellet, Charles (1810–62): 136, 137

engineering concepts

beam theory: 82

buckling: 93

design loads: 83-84, 89

displacement: 80-81, 93-94, 97

elasticity: 79-80

equilibrium: 79, 97

equilibrium polygon: 99

force: 78-79, 81, 83-84, 88-89, 99-100,

103-4, 108

force polygon: 98-99

geometric compatibility: 80

lateral instability: 93

loads: 80, 83, 84-89, 93-95

method of joints: 79, 99

modulus of elasticity; also, Young’s 

modulus: 79

parallelogram of forces: 98

prestressing: 59, 60, 105-6, 133-34,

143-45, 152

strength: 79

stress: 79, 80, 93

statically determinate and

indeterminate: 81, 95

structural analysis: 81

Essex Merrimack River Bridge: 71 (n. 11), 72 (n. 14)

Federal Highway Administration: 33, 39, 195

Feedwire Road Bridge: 148

Felton Bridge: 62

Fischetti, David C. (1946–2011): 109, 192, 193, 199

Fletcher, Bela (1811–77): 15, 128

Fletcher, Robert: 126, 193

Flint Bridge: 7

Forest Products Laboratory: 39, 44

Forsythe Bridge: 123, 165, 171 

Fort River Bridge: 49

Germantown Bridge: 29

Ghega, Carl (Carlo) Ritter von (1802–60): 140-41 

Gilpin’s Falls Covered Bridge: 39, 177 

Gorrill, William Henry (1841–74): 25, 161, 170, 174

Graton Associates: 102, 165 

Graton, Milton S. (father, 1908–94): 6, 7, 10, 17, 

176-77, 176; Arnold (son): 17, 165, 178
Index 231

Great Bridge (Charles River): 71 (n. 7)

Grubenmann, Johannes (1707–71) and Hans 

Ulrich (1709-83): 50-51

Haldorson, Ole (1913–2013): 141

Hale, Col. Enoch (1733–1813): 51, 118

Hall Bridge: 17, 102, 165

Hancock-Greenfield Bridge: 30, 69

Harpole Bridge: 64 

Harshman Bridge: 27

Hassard, Thomas: 132 

Haupt, Gen. Herman (1817–1905): 86, 98, 100, 108, 

109, 122, 123, 125-27, 128, 129

Hendricks Bridge: 167

Historic Covered Bridge Committee, Vermont: 197

Holliwell Bridge: 14, 63

Honey Run Bridge: 62, 144

Horse Creek Bridge: 162

Howe, William (1803–52): 60-61, 106, 133, 135, 136-37

Huffman Mills Bridge: 164

Humber, William: 129-30

Humpback Bridge: 8, 32, 36, 97, 119, 188

hurricanes

Hurricane Irene: 8, 41, 42, 173, 187

Hurricane Lee: 187

Indiana Historical Society: 194

Irish Bend Bridge: 75 (n. 62)

Jackson Bridge (Baltimore & Ohio Railroad): 82,

86, 91, 130-33, 131

Jackson Covered Bridge (Indiana): 12, 123

Jasper Road (“Mud Lick”) Bridge: 148 

joinery: 103-10

Jouravsky, D. I.: 140 

Kauffman’s Distillery Bridge: 173

Kennebec Bridge (Maine): 166

Kennedy family, Archibald M. (father, 1818-97); 

Charles F. (son); Karl (grandson); Charles R.

(grandson): 170-171; Emmett L. (son, 1848-1938): 159, 170

Kenyon Bridge; also Blacksmith Shop Bridge: 9

Kidd’s Mill Bridge: cover, 24, 148, 150, 151-52

King, Horace (1807–85): 15, 172, 182;

Washington W. (son): 15

Knight’s Ferry Bridge: 19, 36

Larwood Bridge: 22, 69

Long, Col. Stephen H. (1784¬–1864): 18, 58-60, 59, 86,

105-6, 130, 133-35; Moses (brother): 59, 132-33

MacNeill, Sir John Benjamin: 128

Mahan, Dennis Hart (1802–71): 82-83, 103, 104, 106-7,

117-19, 118

Massachusetts Department of Public Works: 69, 196

materials

concrete: 166, 197

iron, cast: 61, 64, 91-92, 152 

iron, wrought: 60, 92-93, 92, 106, 142-44

steel: 30, 93, 169, 177, 192, 197-98, 197

stone: 101-2, 164, 166, 180 (n. 15)

timber: 44-45, 50, 90-91, 142, 152, 166-67,

180 (n. 16)

mathematical modeling: 97-100

McCall’s Ferry Bridge: 56, 121, 123

McCallum, Daniel (1815–78): 27

McMellen, Elias (1839–1916): 12, 172-73, 197

Mohawk River Bridge: 120, 121

Moose Brook Bridge: 45-46, 45, 64

Morrison, David H.: 29 

Msta Bridge: 140

National Historic Landmark: 8, 11, 17, 19, 32, 35, 36, 

42, 198

National Park Service: 32, 33, 37, 41

National Society for the Preservation of Covered

Bridges: 45, 190-93
232 Covered Bridges and the Birth of American Engineering

Litwin, Leo: 188, 190

World Guid to Covered Bridges: 33, 189

Navier, Claude-Louis-Marie-Henri (1785–1836): 80-83,

81, 85, 88, 97-100, 134

Neal Lane Bridge: 7

Newport and Cincinnati Bridge: 87

Newfield Bridge: 185

Norris Ford Bridge: 159

North Enosburg Covered Bridge: 187

Office Bridge: 22

Oregon State Highway Commission: 7, 68

Paddleford, Peter (1785–1859): 25, 60, 163, 179 (n. 9);

Philip H. (son, 1815-76): 60

Palladio, Andrea (1508–80): 52, 117, 118

Palmer, Timothy (1751–1821): 52-53, 52, 119

Partridge, Reuben L. (1823–1900): 28, 65

patents; see also, truss types

Burr-arch truss: 56-57, 119, 122, 130

Haupt truss: 127, 128

Howe truss: 60-61, 106, 133, 135, 136-38, 

139-140, 143

Long truss: 59, 82, 105, 108, 130-35, 131, 143, 163

Pratt truss: 61-62, 106, 135, 142, 143

Smith truss: 65, 145-46, 147-150, 174

Town lattice truss: 57, 124-27, 125-26, 130, 175

Pengra Bridge: 75 (n. 60), 176

Pennypack Creek Bridge: 52

Pine Bluff Bridge: 20, 61, 142

Pine Brook Bridge: 6

Pine Grove Bridge: 12, 56, 160, 182 (n. 36), 197

Portland-Columbia Bridge; also “Coca-Cola” Bridge: 67

Post, Simeon: 26

Pottersburg Bridge: 28

Powder Works Bridge: 25, 36, 66, 149, 170

Powers, Nichols Montgomery (1817–97): 17, 36, 58, 110,

173, 179 (n. 3), 87

Powerscourt Bridge: 27, 34

Pratt, Caleb (father) and Thomas Willis (son, 1812-1875): 

23, 61-62, 106, 142

Pratt, Henry B. Jr.: 30

preservation: 36, 39-40, 190-99

Prevost, Lewis M.: 109, 125, 139

Quaboag River Bridge (Western Railroad): 60

railroads

Baltimore and Ohio Railroad: 82, 130-31

Boston and Maine Railraod: 21, 64, 126, 127,

175, 193

Nikolaev Railway; also St. PetersburgMoscow Railway: 139-40, 140

Western Railroad; later Boston and 

Albany Railroad: 60, 136, 137-39

Ramsour, Andrew: 26

Rinard Bridge: 151 

Roseman Bridge: 14, 67

Salt Creek Bridge: 148, 195-96, 196

San Marcos River Bridge: 66

Schuylkill Permanent Bridge: 52-54, 53, 164 

Seguin, Marc (1786–1865): 85, 86 

Sewell’s Bridge: 71 (n. 7)

Schaffhausen Bridge: 50-51, 83

Sherman, Everett: 27

Shoreham Railroad Bridge: 20, 181 (n. 25)

Short Bridge: 162

Smart, George: 128, 129, 155 (n. 27)

Smeaton, John: 89 

Smith, Robert W. (1833–98): 24, 65, 145-50, 174 

Smith’s Bridge: 31

Snow, J. P. (Jonathan Parker) (1848–1933): 16, 126-27, 

159, 175, 193

Snyder Brook Bridge: 21, 74

Speakman’s Mill No. 1 Bridge: 195
Index 233

Stone, Amasa (1818–83): 60-61, 88, 138, 168

Stone, Andros B.: 168

Striker, Aaron Noble (father): 176;

Arthur Clayton (“Art”) (son, 1885-1962): 176

structural

analysis: 81-83, 97-100, 111, 144-45 

design: 77-80, 83, 93-97, 100, 110-12

substructure

abutments: 101-3, 164, 166

piers: 101-2, 101

Sulphite Railroad Bridge: 23, 62, 74 (n. 46), 144, 145

Sunday River Bridge: 25, 163 

Swann Bridge: 16, 63

Taftsville Bridge: 8, 166, 180 (n. 19)

Tannery (Goodhue) Bridge: 191

Tasker, James F.: 9, 15, 128, 166 

Telford, Thomas: 85 

Thomas, Capt. Charles: 156 (n. 34), 163

Thomas Viaduct: iii

Tournon-Tain Suspension Bridge: 85, 136 

Town, Ithiel (1784–1844): 57-58, 109, 124-30

Trautwine, John C.: 87 

Tredgold, Thomas (1788–1829): 90-91, 98, 100, 103-4, 

108-9

Trenton Bridge: 120

truss types; see also, patents 

bowstring truss: 29

boxed pony: 21, 37, 45, 46, 63, 64

Brown truss: 28

Burr-arch truss: i, 10-12, 31, 35, 37, 43, 56,

57, 102, 119-121, 122-25, 130, 147-48, 152, 160,

161, 163, 164, 168-69, 171, 172, 173, 186, 197

Childs truss: 27

deck truss: 23, 63, 94, 144

Haupt truss: 26, 127, 128

Howe truss: 18-22, 36, 45, 46, 56, 60, 61, 62,

68, 69, 88, 90-92, 94, 126, 136-40, 141-43, 149,

161, 162, 166, 167, 168, 174, 176, 190

kingpost truss: 6-7, 56, 81, 83, 97, 118-19

Long truss: 17-18, 42, 44, 58, 59, 60, 130,

131-134, 135, 163, 173

McCallum truss: 27

multiple-kingpost truss: 8-9, 32, 36, 56, 96, 

100, 103, 119, 123, 142, 145-47, 150

Paddleford truss: 25, 60, 163, 165, 167

Partridge truss: 28, 65

pony truss: 63,64, 94, 175

Post truss: 26

Pratt truss: 23, 62, 92, 106, 135, 141-45, 142, 

144, 152

queenpost truss: 7, 14, 34, 56, 96, 103, 118

Smith truss: cover, 24-25, 36, 65, 66, 107,

145-52, 147-150, 161, 167-68, 170, 174, 175

St. Andrew’s cross: 136, 137, 141

TECO (Timber Engineering Company) 

truss: 30

Town lattice truss: 13-17, 36, 43, 46, 57-58, 

63, 100, 102, 109, 100, 124-27, 130, 163, 165,

166-67, 172-74, 175, 192-93, 197

Wernwag truss: 54, 105, 163-64

Wheeler truss: 29, 65

Tverca River Bridge: 140

Union Bridge: 56

Union Street Bridge: 69

U.S. Army Corps of Engineers: 58, 61, 64

Verebia Bridge: 140

Vermont Historic Bridge Program: 196

Village Bridge: 10

Waddell, J. A. L. (John Alexander Low) (1854–1938): 86

Walker, W. T.: 174

Waterford Bridge: 120-21, 120

Watson Mill Bridge: 15
234 Covered Bridges and the Birth of American Engineering

Wells, Rosalie: 188

Wernwag, Lewis (1769–1843): 54, 105, 119, 121, 161

West Union Bridge: i, 43, 96, 102, 169 

Wettingen Bridge: 50-51, 83

Wheeler, Isaac H. (1815–75): 29, 65

Wheeling Bridge: 174

Whipple, Squire (1804–88): 65, 86, 91, 98-99, 109, 129

Whistler, George Washington (1800–49): 60, 132, 137-40

White’s Bridge: 28

Whittier Bridge: 176

Wilson, Raymond E.: 74 (n. 54), 151

Wright’s Bridge: 175

Yadkin River Bridge: 57, 124