NBS BUILDING SCIENCE SERIES 100

Building To Resist The Effect Of Wind

VOTTTME 3. A Guide for Improved Masonry

and Timber Connections

in Buildings

TA

.U58

NO. 100

V 3 ^TMENT OF COMMERCE • NATIONAL BUREAU OF STANDARDS

MAY 1 NBS BUILDING SCIENCE SERIES 100-3 T ^

Building To Resist

The Effect Of Wind

VOLUME 3: A Guide for Improved Masonry

and Timber Connections

in Buildings

S. George Fattal

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

G. E. Sherwood and T. L. Wilkinson

Forest Products Laboratory

Forest Service

US Department of Agriculture

Madison, Wisconsin 53705

Sponsored by: The Office of Science and Technology

Agency for International Development

Department 'of State Washington, D.C. 20523

and

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director

Issued May 1977
Library of Congress Catalog Card Number: 77-600013

National Bureau of Standards Building Science Series 100-3

Nat. Bur. Stand. (U.S.), Bldg. Sci. Ser. 100-3, 56 pages (May 1977)

CODEN: BSSNBV

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1977

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402

(Order by SD Catalog No. Cl3. 29/2:100-3). Stock No. 003-003- Price $2.00 (Add 25 percent additional for other than U.S. mailing).
ABSTRACT

The Agency for International Development sponsored with the National Bureau of Standards, a three and a half year research project to develop improved

design criteria for low-rise buildings to better resist the effects of extreme winds. This report contains in- formation gathered from this project.

Project results are presented in five volumes. Volume

1 gives a background of the research activities, ac- complishments, results and recommendations.

Volume 2 presents a methodology to estimate design

wind speeds and a guide to determine wind forces. Volume 4 furnishes a methodology to estimate and

forecast housing needs at a regional level. Socio- economic and architectural considerations for the

Philippines, Jamaica, and Bangladesh are presented in Volume 5.

This report investigates the use of connectors for masonry and timber elements in low-rise buildings.

Connector characteristics and construction details that improve a building's response to extreme wind

effects are given primary emphasis. Retommendations include improvements through better utilization of connector technology showing good feasibility of introduction in developing countries. The building

systems considered in this study fall within the low to moderate cost category.

Key words: Codes and standards; connectors; fasteners; lowrise buildings; masonry walls; structural design; technology

transfer; timber roofs; timber walls; wind effects.

Hi

Cover: A new housing project, formerly a squatter

settlement, in Kingston, Jamaica.

Contents

ABSTRACT

1. BUILDING SYSTEMS

1.1 Introduction 1 1.2 Roof Systems 2

1.3 Pole Type Construction 2

1.4 Masonry Bearing Wall System 3 1.5 Timber Wall System 3

2. MASONRY CONNECTORS 7

2.1 Introduction 7 2.2 Types of Masonry Construction 8

2.3 Analysis of Wind Damaged Buildings 9 2.4 Masonry Construction in Developing Countries 10 2.5 Masonry Practices in the United States 13 2.5.1 Available Masonry Connectors 22 2.5.2 Available Technical Information 12 2.6 Suggested Improvements in Masonry Construction 22

2.6.1 Utilization of Available Connectors 22 2.6.2 Improved Construction Practices in Severe Wind Environment 22

3. FASTENERS FOR TIMBER CONSTRUCTION IN HIGH WIND AREAS 27

3.1 Introduction 27

3.2 Available Timber Fasteners 28

3.2.1 Nails, Screws, Bolts, and Lag Screws 28

3.2.2 Timber Connectors .- 28

3.2.3 Truss Plates 28

3.2.4 Sheet Metal Fasteners and Other Special Devices 28

3.3 Philippine Timber-Related Practices 28

3.3.1 Pole Type 29

3.3.2 Wood-Framed Wall and Roof 29

3.3.3 Masonry Wall 29

3.3.4 Roof Framing 29

3.3.5 Roofing 29

3.3.6 Protection From Wood-Destroying Organisms 30

3.3.7 Summary of Good and Poor Practices 30

3.4 Timber Fasteners Appropriate for Construction in Developing Areas With High Winds 30

3.4.1 Pole-Type Construction 30

3.4.2 Light Wood-Frame Construction 30

3.4.3 Concrete and Masonry Construction 32

3.4.4 Roof Framing 32

3.4.5 Roofing 32

3.5 Fasteners for Fabrication by Indigenous People 32

3.6 Summary 31

3.7 A Caution 32

REFERENCES 47

ACKNOWLEDGMENTS 48

V
Figures

1. BUILDING SYSTEMS

Fig. 1 Common roof systems for low-rise buildings 3

Fig. 2 Pole-type construction 4

Fig. 3 Miscellaneous bamboo and non-dimensioned lumber connection details 5

Fig. 4 Masonry bearing wall construction 6

Fig. 5 Timber wall construction 6

2. MASONRY CONNECTORS

Fig. 6 Concrete masonry units 13 Fig. 7 Infill wall masonry construction H

Fig. 8 Collapse of one-story building caused by the November 1974 typhoon in the Philippines 14

Fig. 9 Failure of metal anchor plate in building destroyed by the November 1974 typhoon

in the Philippines 15

Fig. 10 Roof failure in building caused by the typhoon in November 1974, in the Philippines 15

Fig. 11 Single family houses damaged or destroyed by the typhoon in November 1970, in Central Luzon, the Philippines J6

Fig. 12 Single family house showing collapse of roof and exterior wall during the Philippines typhoon in November 1970 16

Fig. 13 Interior damage of single family house caused by the November 1970 typhoon in the

Philippines 17

Fig. 14 Residential building in Darwin, Australia destroyed by the December 1974 cyclone 17

Fig. 15 Building of cavity wall construction in Darwin, Australia, partially destroyed by the

December 1974 cyclone 18 Fig. 16 Building in Darwin, Australia showing partial collapse of roof and masonry infill walls caused by the December 1974 cyclone 18 Fig. 17 Failure of concrete block masonry wall in building subjected to the December 1974

cyclone in Darwin, Australia 19

Fig. 18 Single family masonry house under construction in Central Luzon, the Philippines 19

Fig. 19 Stacked bond concrete masonry wall construction for single family occupancy in Central Luzon, the Philippines 20

Fig. 20 Single family housing development in Central Luzon, the Philippines 20

Fig. 21 Concrete columns with concrete masonry infill walls being constructed for single

family dwelling occupancy in Central Luzon, the Philippines 21 Fig. 22 Construction of single family housing unit in Central Luzon, the Philippines, showing concrete masonry filler walls and reinforcement of corner column 21

Fig. 23 Reinforced concrete masonry dwelling unit in Central Luzon, the Philippines. ... 22

Fig. 24 Reinforced concrete masonry walls under construction for housing in Central

Luzon, the Philippines 22

Fig. 25 Concrete masonry bearing wall construction with truss type roof for housing in Central Luzon, the Philippines 23

Fig. 26 Single family housing under construction in Central Luzon, the Philippines, showing concrete bond beam detail over openings 23

Fig. 27 CARE sponsored housing project near Dacca, Bangladesh showing cinva-ram wall

construction with corrugated metal roofing 24

Fig. 28 Various metal anchors: (a), (b) tiebars with end hooks; (c) tiebar with hook and split

hook; (d) tiebar with 90° twist; (e) corrugated dovetail tie; (f) corrugated tie; (g) dovetail tie with hook; (h) anchor bolt 24

vi
Fig. 29 Application of metal anchors in masonry construction: (a) tiebar anchor to wood

joists; (b) twisted anchor connecting wood joist to concrete masonry bearing wall; (c) tiebar anchor connecting concrete masonry intersecting walls 25

Fig. 30 Application of anchor bolt for masonry connection: (a) connection of sill plate to concrete masonry bearing wall; (b) connection of concrete masonry wall to wood

stud wall , 25

Fig. 31 Joint reinforcement in masonry walls: (a) truss; (b) ladder; (c; and (d) prefabricated corner section; (e) and (f) prefabricated tee section 26

Fig. 32 Horizontal reinforcement between intersecting masonry walls: (a) and (b) without

bond beams; (c) and (d) with bond beam 26

3. TIMBER FASTENERS

Fig. 33 Various types of nails: A, bright, smooth wire nail; B, cement-coated; C, zinc-coated;

D, chemically etched; E, annularly threaded; F, helically threaded; G, helically

threaded and barbed; and H, barbed 32

Fig. 34 Joint with split-ring connector showing connector, precut groove, bolt, washer, and

nut 32

Fig. 35 Joint with toothed-ring connector 33

Fig. 36 Joints with shear-plate connectors with A, wood side plates; and B, steel side plates 33

Fig. 37 Some typical truss plates 34

Fig. 38 Some examples of special fasteners made by the Timber Engineering Company ... 34

Fig. 39 Pole-type construction 35

Fig. 40 Wood-frame wall and roof 35

Fig. 41 Concrete block wall with wood frame roof 36

Fig. 42 Roof framing tied down with strips of bamboo 36

Fig. 43 Thatch roof with thatch partially blown off 37

Fig. 44 Covering material on the outside protects framing and connectors 37

Fig. 45 Anchor bolt and sill plate exposed to weather present decay hazards 38

Fig. 46 Metal strap on only one side of framing failed to resist bending load 38

Fig. 47 Collar ties hold rafters from pulling apart at the peak 39

Fig. 48 Ceiling joist bolted to rafter resists outward thrust of rafter. Wood cleats tie purlins to rafters 39

Fig. 49 Sheet metal strap nailed to one side of purlin and riveted to corrugated roofing . . 40

Fig. 50 Although the roof blew off of the structure, the corrugated roofing was effectively

tied to purlins by wires completely around the purlins 40

Fig. 51 Joint failure due to decay in wood 42

Fig. 52 Staining from corrosion of bolts and nails 41

Fig. 53 Round pole notched for sawn framing member 42

Fig. 54 Two framing members butted end-to-end over flat notch and bolted to a pole .... 42

Fig. 55 Anchor bolt in concrete a minimum of 8 inches. Washer to spread load 42

Fig. 56 Anchor bolt through concrete block foundation into footing 42

Fig. 57 Anchor bolt installed on protected side of wall 43

Fig. 58 Sheet metal strap tying stud to bottom plate 43

Fig. 59 Sheet metal bracket for tying roof framing to walls 43

Fig. 60 Wood cleats nailed to each side of roof framing and to top plates 43

Fig. 61 Sheet metal strap nailed to ceiling joist and stud to anchor roof framing to wall . . 44

Fig. 62 Sheet metal bracket used to connect purlin to rafter 44

Fig. 63 Purlins tied to rafters by wood cleats -^^

Fig. 64 Two metal straps riveted to corrugated roofing, lapped under purlin and nailed to purlin "^-^

Fig. 65 Multipurpose strap. Length and width can be varied for specific applications 45

vii
Fig. 66 Galvanized sheet metal strap with rivet and washer for tying down corrugated roof- ing 45

Fig. 67 Multipurpose bracket fabricated from 20-gage galvanized steel. Bend either direction

at bend lines to form desired bracket 45

Fig. 68 Split-ring connector for indigenous fabrication (left), and commercially produced

split-ring connector (right) 46

Fig. 69 Plate connector with barbs 46

viii

Facing Page: Housing project near Manila, Philippines

showing the application of indigenous building material.
1. BUILDING SYSTEMS

by

S. George Fattal .

1.1 INTRODUCTION

This report discusses the use of connectors in houses

and other low-rise buildings to improve their structural response characteristics under extreme wind

conditions. The report is organized into three main

sections. Section 1 presents a general overview of mansonry connectors and timber fasteners. Section 2

is devoted to a detailed discussion of connectors in

building systems using masonr\' wall construction. Section 3 treats fasteners used in buildings of timber

wall construction. These two types of buildings are most prevalent in housing for low to middle income

occupancy in developing countries located in windprone areas [l ].'

' Numbers in brackets indicate references listed at the end of this report.

1
These buildings are typically one or two story

detached units which are supported by a continuous

wall footing made of cast concrete or concrete block

masonry or, in flood-prone areas, by wooden poles

embedded in the ground. The roof is commonly

characterized by a pitched timber frame often projecting up to 1.5 m (5 ft) beyond the exterior walls, and

topped by corrugated metal cover. The types of building- systems of interest to this study

are identified by reference to figures 1 through 5, which also serve as key visual reference for locating

specific connector details discussed in the subsequent

sections of this report.

1.2 ROOF SYSTEMS

Figure 1 exhibits the two most commonly used

framing systems for the roof: (a) the truss type and (b) the joist-rafter assembly. The truss type construction

employs a series of equally spaced trusses spanning

between opposite exterior walls. The corrugated

metal roof cover is attached to a series of longitudinal

purlins connecting the trusses together. The joist- rafter type consists of a system of inclined rafters framing into a ridge beam at the top and attached to ceiling joists spanning between opposite exterior walls at the bottom. Collar beams attached to the

rafters provide stiffness to the roof in the vertical plane. The close spacing of the rafters permits direct attachment of roof cover to the rafters thereby

eliminating the need to use purlins.

The choice of a particular roof system depends on many factors. A joist-rafter assembly allows better

utilization of attic space while the truss system per- mits prior assembly of the individual trusses at the shop where quality control isgenerally better than in the field. Structurally, both systems can be designed to have the desired diaphragm capability to transmit

lateral wind forces to the appropriate shear walls (having the same orientation as the wind as in figure

2, [Reference [2]). For instance, diaphragm rigidity can

be improved by introducing horizontal cross-bracing

in the plane of the joists and vertical cross-bracing in the longitudinal ridge plane (perpendicular to the

joists) of both systems shown in figure 1 . A practical but somewhat more expensive alternative to the horizontal bracing would be to provide wood flooring fastened to the joists in a manner that will insure in- tegral action in the horizontal plane.

The importance of diaphragm action for roof systems

in extreme wind regions should be emphasized in the

light of the types of roof and wall failures observed

that were attributed to a lack of transverse rigidity of the roofing system, as noted in section 2. The use of timber fasteners for connecting roofing elements is discussed in section 3.

1.3 POLE-TYPE CONSTRUCTION

Figure 2 shows the structural layout of a pole-type

construction. The raised floor protects the house

against insect infestation and floods. This type of construction provides generally a lower cost housing

than either masonry or wood frame wall system since

it lends itself more readily to auto-construction (self- help). It also permits utilization of less expensive in- digenous products such as nondimensioned timber

(logs) for the poles, and cane (i.e., bamboo) framing

with rattan or twisted cane connectors as shown in figure 3. The figure also illustrates suggestions for adequate joining of members. The poles should be treated

against insect infestation and water penetration prior

to being embedded into the ground. The length

of embedment required to resist wind-induced uplift or overturning and to provide adequate bearing is determined by local soil conditions. Figure 2 shows

footing schemes for the poles and for the dimensioned

timber post used as an alternative. Note that shallower embedment will require more substantial footings for the same level of resistance against windinduced uplift forces. The design should also account

for the additional uplift forces under the exposed

floor.

Since the poles are the main pillars of support for the

superstructure, they should preferably extend to the top and be provided with adequate connections at the

roof and at the floor level. Because of their unsupported length between the raised floor and the ground, these poles should be proportioned to pro- vide adequate flexural resistance to lateral forces in- duced by extreme winds. If this is not altogether feasi- ble from a practical design standpoint, vertical cross- bracing made of wood, bamboo or wire cable should

be introduced to tie the poles together below the floor

level. Cables and various tiedown straps used in the United States to protect mobile home installations against extreme winds should also be explored for use

in buildings on poles to provide additional stability

against uplift and overturning forces. Information on

available tiedown and anchoring devices may be ac- quired from the Manufactured Housing Institute.

-

Design provisions for mobile home tiedowns are prescribed in Chapter 6 (1974) and appendix D(1975)

of ANSI A119.1[4j, and reference l5j supplies

guidelines for their design. Section 3 discusses

fasteners used in pole-type housing. Supplementary

information on pole-type construction and the structural use of bamboo may be acquired by consulting

references [6] and l7j.

-Manufactured Housing Institute, P.O. Box 201, Chantilly,

Virginin 22021.

2
1.4 MASONRY BEARING WALL SYSTEM 1.5 TIMBER WALL SYSTEM

Figure 4 displays the structural layout of a masonry

bearing wall building system. The single wythe walls

(defined in section 2.2) are built with hollow concrete masonry units which permit the passage of vertical reinforcement without the need of addtional wythes. Note that alternate schemes are available for constructing lintels and peripheral (or collar) bond beams.

They are indicated in the same figure for generality

and convenient referencing purposes.

It was noted earlier that the type of masonry dis- cussed in this report is generally representative of masonry housing construction in developing countries (1 J. This makes it unnecessary to consider

diverse masonry systems such as multiple wythe construction (to permit vertical reinforcing when solid units are used) or masonry veneers and other nonloadbearing elements. However, section 2 does consider one additional masonry system (generally re- ferred to as an "infill frame") which consists of a concrete frame with masonry filler walls.

Figure 5 shows a partial view of a timber "stud" wall system. The studs or "verticals" transmit gravity loads and the vertical component of wind-induced

loads which may be reversible (bearing or uplift). In addition, the studs provide flexural resistance against

direct horizontal wind pressure or suction. The

diagonals stiffen the walls in their own planes and in- crease the capability of the system to resist lateral loads. The specfic fastener details for the stud wall system are discussed in section 3.

(b) JOIST-RAFTER ROOF SYSTEM

FIGURE 1 COMMON ROOF SYSTEMS FOR LOW-RISE BUILDINGS.

3
EMBEDDED

POLE

POLE WITH

CONCRETE

FOOTING

CONCRETE COLLAR

PERMITS SHALLOWER

EMBEDMENT

POLE WITH

CONCRETE

FOOTING

FIGURE 2 POLE-TYPE CONSTRUCTION

4

ROOF TOP PLATE

CONCRETE WALL FOOTING FIGURE 4 MASONRY BEARING WALL CONSTRUCTION.

FIGURE 5 TIMBER WALL CONSTRUCTION.

Facing Page: These reinforcing bars add strength to the building frame and insure a positive connection between

the roof and walls.

6
2. MASONRY CONNECTORS

by

S. George Fattal

2.1 INTRODUCTION

This section discusses the use of masonry connectors

in bearing wail construction for improved structural response under severe wind conditions. The struc- tures considered are low-rise buildings(i.e., dwellings, small business stores, community centers, schools) in developing countries. For the purpose of

this section the word "connector" is used to designate

any mechanical device, including reinforcing bars, which can be effectively used to connect individual

masonry walls to the other elements of the system

(walls, columns, beams, partitions, roof or foundation).

The material in this section consists of an introducto- ry discussion giving background information on masonry construction, exhibits and analyses of build- ings damaged by extreme winds, a survey and evalua7
tion of current masonry practices in developing countries experiencing high winds, a study of current masonry practices in the United States relating to high winds and earthquakes with a discussion of various types of masonry connectors employed in such construction, and general and specific recom- mendations for improving high wind response of masonry buildings in developing countries through

better utilization of existing connector technology.

2.2 TYPES OF MASONRY CONSTRUCTION

Masonry bearing walls used in low-rise buildings in developing countries are commonly built with hollow

concrete masonry units. Figure 6 shows some of the common types of masonry units used in the United

States [8]. Although the standard unit shown has 2

cores, 3-core units are also quite common in the United States as in the Philippines and other developing countries. In running bond construction (vertical

joints staggered), it is somewhat easier to place vertical reinforcement through the 2-core units because the cores are in vertical alignment. They are also more

modular than the 3-core units (less number of shapes

and sizes are required in construction). For additional

information, detailed classifications of concrete masonry are found in ASTM Designations C90, C129,

C140, C145and C331[9],

Masonry units are laid in mortar which acts as their binding agent. Prevailing types of mortar in the United States are cement-lime-sand and masonry ce- ment-sand mortars. Different proportions of the constituents in these types will produce different strength

properties. Standard mortar designations, such as types M, S or N are used for the appropriate mortar

identification according to the range of constitutent proportions, by volume, specificed in ASTM Designation C270 [9]. Types M, S, and N are commonly used

for structural masonry applications. Types M or S are

specified for high flexural strength requirements.

Various other specifications for mortar and mortar in- gredients are found in ASTM Designations C5, C91,

C109, Clio, C144, C157, and C207[9].

Masonry walls are classified according to type of construction and intended use in a building. A single

wythe wall has one masonry unit in its thickness. A

multiple wythe wall has several masonry units in its thickness. In a composite wall construction, at least one

of the wythes is built with masonry units dissimilar from those in the neighboring wythes. Multiple

wythe walls without cavity are laid contiguously

with the spaces between the wythes, called collar

joints, filled with mortar or grout. To insure

monolithic action of the assembly, additional bonding

is effected by the use of metal ties laid horizontally in bed mortar across the wythes at periodic intervals

throughout the height of the wall. A cavity wall is identified by a continuous vertical air space between

any two adjacent wythes and by metal ties laid as in composite wall construction and connecting the two

wall sections flanking this space. Reinforced masonry

walls built with solid units are reinforced by placing

steel bars, vertically and/or longitudinally, as needed,

in the space between consecutive wythes and by

grouting this space. In hollow block walls, such as those studied in this report, vertical reinforcement

may be placed as needed, through the hollow cores which are then grouted.

The following types of masonry walls are identified by their intended function in a building. A load-bearing wall supports the vertical loads above it, in addition to

its own weight, with or without the aid of a vertical load-carrying space frame. A nonload-bearing wall supports no vertical load other than its own weight. A

shear xvall resists planar forces induced by exterior horizontal loads acting on a building. A curtain wall is a non-load bearing wall, built outside the building

frame and not entirely supported at each floor. A

panel wall is a non-load bearing exterior wall sup- ported at each floor. A partition is a non-load bearing

interior space divider which will function as a shear wall unless isolated along three edges from the rest of the structure. Veneer is the exterior masonry layer of a two-layer wall system, connected to the interior layer

and/or to the primary load-supporting structure by

horizontal ties. Veneer is generally designed to be

non-load bearing. A pier is a masonry wall segment

flanked by two adjacent openings or by an opening

and the vertical edge of a wall. A lintel is a wall seg- ment above an opening.

A masonry filler wall or infill wa// designates a wall

fully enclosed within a structural frame or bounded

by two columns and wholly supported at each floor

level. Filler walls may be load-bearing or non-load

bearing depending on the type of construction. In the United States, filler walls are generally non load bearing because they are usually laid after the frame

has been erected so that only mortar bond exists at the

interface. Figure 7 shows another type of filler wall

construction where the walls are laid first on top of a wall footing, followed by casting of the concrete col- umns and peripheral bond beam. This scheme permits

extension of horizontal and vertical wall reinforce- ment into the surrounding frame so that the assembly

will act integrally under superimposed loading. This

system is widely used in the Latin American countries and has shown good performance under severe earth- quakes in the past. The latter type of infill wall construction and the

single wythe masonry bearing wall construction

shown in figure 4 are the two types of masonry

systems considered in this Volume.

8
2.3 ANALYSIS OF WIND DAMAGED

BUILDINGS

Figures 8 to 17 exhibit buildings damaged or destroyed

by recent hurricanes and typhoons. The buildings

shown in figures 8 to 10 belong to a group of one-story

structures in Northern Luzon, the Philippines,

which either sustained severe damage or collapsed as a result of the November 1974 typhoon. These struc- tures consisted of masonry walls and wood posts, a pitched roof system of wood trusses, purlins and cor- rugated iron cover, and a continuous foundation wall

of cast concrete.

Figure 10 exhibits a typical failure of the fasteners connecting the purlins to the top chords of the trusses. Most of the roofing was "peeled off" in this manner.

Portions of the corrugated iron roofing found on the ground contained the purlins with their metal wire

attachments still in place (fig. 50). Instability of the

trusses, few of which were still standing, was at- tributed to the loss of purlins and the absence of other

longitudinal bracing between the trusses. The collapse

of the masonry walls as shown in figure 8 was

likewise attributed to the loss of lateral support at the roof level. However, the extent and severity of wall damage is also attributed to the absence of connections

between abutting walls and the ineffectiveness of the

vertical anchorage at the base. As indicated in figure

9, the only anchorage consisted of steel plates bolted

to the wood posts. Close inspection revealed severe

corrosion of these plates, especially at the ruptured

section through the bolt-holes (fig. 9). The masonry

walls in these buildings were nonload-bearing as they were stopped short of the roof to provide openings at the top (fig. 8). Thus the wood posts were the only

vertical load-bearing elements and with the loss of the roof many of the corner posts were tipped over (fig. 8).

Figures 11 to 13 show single family housing units of concrete masonry bearing wall construction, located

in Central Luzon, the Philippines, that were damaged

or destroyed by the November, 1970 typhoon. An in- herent weakness of these systems is the absence of peripheral support of the masonry walls at the top

because of a local preference for large openings at these locations. This practice reduces the effectiveness

of the roof to function as a diaphragm and makes it more susceptible to failure by wind suction or uplift. As indicated in figure 11, most of the roofs of these

units were removed by the storm. Inspection of

figures 12 and 13 indicates good quality workmanship

was used in constructing the masonry walls which contained vertical reinforcement in grouted

cores. Note that the nails between the top window

frame insert and the wall below or the peripheral

wood joist above were not effective in preventing the

masonry wall from caving in (fig. 13) or in keeping

the inserts from falling down (fig. 12). In fact, there is no evidence that any fasteners were used between the wall panel (in the background of fig. 12) and the peripheral joist on top which was probably removed

together with the roof by the storm.

Figures 14 to 17 exhibit structures consisting of

different types of masonry wall systems that sus- tained severe damage or were destroyed by the December 1974 cyclone in Darwin, Australia. These

structures represented engineered masonry construction with respect to the quality of workmanship and

adherence to Australian masonry codes and standards

(which are comparable to those in the United States). The Darwin experience demonstrated that compliance with current standards does not necessarily

produce a structure capable of resisting the estimated

65 m/s(150 mph) winds experienced during this storm. However, it does indicate the need to reex- amine the existing provisions with the objective of developing improved design criteria, connection

details, and construction practices in order to mitigate the extent of damage associated with extreme winds.

A damage study of the Darwin structures reveals some features worthy of note. In figure 15, it appears

that failure occurred at the fourth bed joint from the

top, in the inner concrete masonry wythe of the double-wythe cavity wall. Since the inner wythe is the loadbearing component, its failure was probably

caused by an outward thrust of the roof under the ac- tion of wind. The tilted position of the inner wythe

with its top leaning against the brick facing indicates the absence of ties between the wythes near the roof

level. The masonry wall in fugure 14 consists of two

concrete block wythes with a cavity in between. The

condition of the reinforcement demonstrates the in- effectiveness of the light-gage ties in assisting the in- tegral functioning of the two wythes in out-of-plane

flexure.

Figure 16 shows an infill wall construction with a

steel frame and concrete masonry filler walls. There is no visual evidence of any reinforcement having been

used in the filler walls. Note the severity of vertical cracking through the wall on the right and also the separtion between the steel column and the wall at the left. It is not possible to establish by examination

of the figure whether there were any connectors bet- ween the steel columns and the filler walls. Figure 17 shows the portion of a concrete masonry wall under

the sill of a large window opening that has failed. Note that the top course was connected to the window frame with anchor straps embedded into the grouted cores. It is likely that failure was caused by

the movement of the window frame, prying the top

course loose from the rest of the wall.

9
2.4 MASONRY CONSTRUCTION IN

DEVELOPING COUNTRIES

The following discussion pertains to masonry buildings representing the types of construction used in developing countries. Local practices, utilization of building products, standards compliance, etc., are dis- cussed and evaluated with the aid of exhibits of buildings at various levels of completion.

Figures 18 and 19 show two different stages of construction of a single family house located in Central Luzon, the Philippines. The walls are built with 3- core concrete block units (some of which may be seen

lying on the ground in fig. 18). The units are laid in stacked bond to permit placement of reinforcement

through the vertically aligned cores. On the basis of

figure 19 the quality of masonry construction is deemed inferior by existing masonry standards. Some

of the deficiencies noted are: (1) use of defective units,

(2) partially filled and non-uniform mortar joints, (3) insufficient horizontal reinforcement for stacked bond construction, and (4) insufficient lintel reinforce- ment above the openings. It should be pointed out, however, that this system utilizes a peripheral concrete bond beam cast directly above the lintel course

(see fig. 18). From the standpoint of overall structural integrity in a severe wind environment, attention is drawn to the practice of using large roof overhangs

which are particularly susceptible to wind damage as they are subjected to a positive pressure from below

and suction from above [2]. A potentially critical condition also exists in the masonry column supporting a larger overhang at the corner of the landing. Unless

substantial top and bottom anchorage and vertical reinforcement is supplied in the column, which is not

likely to be the case, given the limited available core space in the single unit section, there is a high probability that the column will fail under the impact of windborne missiles and /or uplift forces exerted by

the roof in a severe windstorm.

Figure 20 shows completed single family houses in another project located in Central Luzon, the Philippines. Figures 21 and 22 display the infill wall construction of a typical unit which is judged to be

superior in the overall quality of construction as well

as wind-resistant capacity to that shown in figure 18. Structurally sound features include: (1) the use of run- ning bond (vs. stacked bond) masonry constructionjwith

vertical and horizontal reinforcefnent, (2) adequate

connections between neighboring elements and (3) the practice of casting the column concrete after completion of the infill walls. With regard to item (2), note

for instance, in figure 21, that the vertical bars extend

beyond the top of the column and the walls to provide

connection to the roof. A structurally marginal practice identified by reference to figure 22, is the manner

in which the lintels are built. A wood form is shored

at the top to give the desired height of opening, and

the space is filled with broken concrete block remnants and mortar. After setting, the metal window

frame is fitted into the opening, probably the window

frame is relied upon to carry the weight of the lintel above it in addition to any loads transmitted from the

roof. It is not known whether any horizontal

reinforcement was placed in the courses above the

lintel; none appear to be projecting into the adjacent corner column.

Another example of reinforced masonry bearing wall

construction used in the Central Luzon area of the Philippines is the house shown in figure 23. Although

it is quite similar to the first systems discussed above

(fig. 8), there are some major differences that make it a more viable system structurally. For instance, the use

of lintels cast integrally with the bond beam (figs. 25 and 26) gives better integrity to the system. Likewise,

the hip roof is essentially a space truss which has a better diaphragm capability because it is braced in both horizontal directions. Also note that the amount

of reinforcement (fig. 24) is more substantial, the masonry and workmanship is of a better quality and

better connections are used between the roof and wall elements. The common inherent weaknesses are: the

use of slender columns made by stacking single units

(fig. 23) and excessive projections of the roof overhangs.

Figure 27 shows a house built in Bangladesh by CARE,

Inc., consisting of walls and pilasters built with cinvaram^—masonry units. The wall footings are built wider than the walls and are raised above ground to protect the house against floodwater. One of the at- tributes of this house is its low cost; it lends itself to self-help construction since the skills needed to pro- duce cinva-ram are minimal. One disadvantage of

this construction is the difficulty of reinforcing it economically. Since cinva-ram units are solid, double

wythe walls are needed for the placement of bars. This can be compensated to a certain extent by using- thicker walls built with larger units. The foregoing case studies, which were based on in- formation gathered from field surveys of ongoing

construction projects, indicate the need for a broader

dissemination of existing literature on building construction practice to the public. The reference section

lists some of this information that is available through

local sources such as the Philippine Standards

Association [15 to 18j, the Association of Structural Engineers of the Philippines [20j, the Philippine Bureau of Standards 1 13, 14j, and the Caribbean Council of Engineering Organizations [27j.

^Units made by pressings mixture consisting mostly of clay

and cement into rectangular units which are then dried in the sun.

20
2.5 MASONRY PRACTICES IN THE UNITED

STATES

2.5.1 Available Masonry Connectors

Among the broad variety of connectors available for use in masonry construction, a significantly large

number are utilized for non-structural applications

such as for attachment of facing panels, hangers and

miscellaneous appendages. Others are used in dual wall systems such as cavity walls, wood framing with

masonry veneer and two-wythe walls with rein- forced and grouted collar joints. Both of these categories are excluded in this study since they do not relate

to the single wythe bearing wall construction most commonly used in developing countries.

Figure 28 shows a variety of metal anchors used to tie masonry walls to interconnecting elements. Tiebars come in different sizes and shapes for diverse applications. Where used to provide lateral support between

abutting bearing walls, 6-mm (1/4-in) tiebars with end

hooks are typically placed in alternate courses with

the bent ends embedded in cores filled with mortar or grout as illustrated in figure 29(c). A twisted bar without end hooks is used to tie floor or roof joists to the concrete masonry bearing surface as shown in figure

29(b). These joists are supported laterally, at specified

intervals, by the masonry walls of the same orientation, with tiebars as indicated in figure 29 (a). Tiebars

used in pairs provide an effective means of anchoring

the roof to the walls. At the top the hooks aie lapped

and nailed to the rafter or the top chord of the roof

truss. At the bottom, they are embedded in concrete bond beam or, in the absence of a concrete bond beam,

into the grouted cores of the concrete blocks in the top

course. Steel reinforcing bars can also be used for this purpose. In either case, proper care should be exercised to protect exposed metal surfaces against corrosion.

Plain or corrugated dovetail bars shown in figures

28(e) and (g) are made of lighter gage metal than the

tiebars and are used to tie masonry walls to walls or columns. These anchors require special metal duct in- serts in the concrete to receive the dovetail end in in- terlock. Although dovetail anchors are generally

designed for non-load bearing masonry wall connections, they provide some measure of resistance against

pullout forces. The corrugated dovetail tie with an end hook shown in figure 28(f) provides an effective means of anchoring door and window frames to the masonry walls. Anchor bolts such as the one shown in figure 28 (h) are mainly used to connect wood elements to the masonry.

The bent end generally gives more holding

power for the same length of embedment than the head of a standard straight bolt. Figure 30 illustrates

two anchor bolt applications: (a) anchorage of sill to masonry wall and (b) anchorage of stud wall to masonry

wall. Also consult figures 55 and 56 which illustr'ate the use of anchor bolts to connect a stud wall system to cast concrete slab footings and concrete masonry foundation walls.

Figure 31 shows reinforcement designed for placement in the horizontal joints of masonry walls. The

two common shapes are the truss and the ladder shown in (a) and (b), respectively. This reinforcement

is fabricated from light-gage, cold-drawn steel and

consists of two longitudinal rods welded together by

cross rods. Joint reinforcement is used as a means to prevent or control cracking in masonry walls and to improve their tensile strength in horizontal flexure. The use of joint reinforcement is strongly recom- mended in walls of stacked bond construction which

are prone to develop cracking in service along the

vertically aligned mortar joints. A good practice is to use them in alternate courses in stacked bond construction and in every third course in running bond

construction. Special prefabricated units are also available for continuous reinforcement around cor- ners as in figure 31(c) and (d), and for tying abutting walls and partitions as in figures 31(e) and (f). There are a large number of manufacturers of masonry

connectors. The best source of obtaining names of manufacturers is The Thomas Register [26\ and the best source of obtaining product information is The Sweet's

Industrial Construction Catalog [3|. The pertinent data supplied by the manufacturer include descriptions of the available products, their application, technical data and level of acceptance by building regulatory

agencies.

2.5.2 Available Technical Information

The design and construction of masonry buildings are governed by the provisions of various regulatory

documents. Among these, the principal one for concrete masonry is the NCMA Specification [28] which comes with a Commentary [29j giving the rationale behinr" its provisions. The ACI Committee 531 report

[30j contains proposed recommendations for concrete masonry structures that have been referenced by

Jamaican sources ll J. This committee is currently pre- paring a revised code for concrete masonry. Provisons

for masonry in general, are prescribed in ANSI

A41131J and the Uniform Building Code [32\.

Information of a less technical nature is contained in reference [33j published by NCMA, which provides

guidance for vocational training in concrete masonry.

NCMA also publishes a TEK series |34| which supplies technical information on design, construction

and detailing aspects of concrete masonry.
Experimental and analytical research work on concrete masonry conducted at the National Bureau of Standards is described in various publications media

with the more recent ones included in the reference

list [35 to 39|. Additional sources of information on

concrete masonry-related practices are also listed [40

to 46).

2.6 SUGGESTED IMPROVEMENTS IN

MASONRY CONSTRUCTION

2.6.1 Utilization of Available Connectors

Improvements in building construction can be

effected through better utilization of available masonry

connectors. The methods include the use of tiebars as an expedient means of anchoring masonry walls

together as well as to roof and foundation elements.

Bars of 3 to 6-mm (1/8 to 1/4-in) thickness which

should be locally available in many developing countries can be bent or twisted to give them the desired

configuration by labor-intensive methods much in the same manner as is employed to hook reinforcing bars

in the field.

It was previously noted that connections effected by

tiebars may also be accomplished by using plain or deformed reinforcing bars which are generally more

readily available than tiebars. To be effective, exposed

reinforcing bars should be resistant to corrosive

agents. Where used to connect the roof to the masonry

walls, reinforcement should have sufficient embedment in concrete or grout-in-core at the bottom, and

should preferably extend over and around the connecting roof element and be secured on both sides by

straps nailed to the wood.

To provide anchorage between intersecting walls,

reinforcing bars formed into a loop or hooked at both

ends may be placed in bed mortar for construction

without using bond beams as indicated in figures 32(a) and (b). Where bond beams are utilized, a more substantial anchorage may be effected by bending and ex- tending the bars into the neighboring walls as indi- cated in figures 32(c) and (d). Likewise, walls may be

connected to the foundation by dowels embedded in the footing (bent dowels are preferable) and extending

into the grouted core of the wall and lapping with the

vertical reinforcement.

2.6.2 Improved Construction Practices in

Severe Wind Environment

Improved structural response in a severe wind en- vironment may be achieved through practices which

have been identified through past records to be more

effective during natural disasters. The more important aspects are:

1. Use of peripheral bond beam connecting all load-bearing masonry elements together. Alter- nate construction schemes include the use of a cast concrete beam and the use of bond beam masonry

units through the top course (fig. 4). Both schemes

permit placement of horizontal reinforcement to achieve better integrity at the top. It should also be mentioned that a substantial bond beam

relieves the walls from resisting forces in out-of- plane flexure and supplements the diaphragm

rigidity of the roof.

2. Use of appropriate lintels and connections be- tween lintels and the rest of the walls. Alternate

cast-in-place and precast lintels are indicated in figure 4. A most effective means of achieving continuity of lintels is to cast them integrally with the bond beam as indicated in figure 25.

3. The need for adequate diaphragm capability of the roof cannot be overemphasized. The roof system should preferably be braced in both directions to achieve a measure of diaphragm rigidity

which is needed to transmit lateral wind loads to the appropriate shear wallsbelow.

4. The use of slender vertical elements such as those

built with single stacked concrete masonry units

to provide columns for the support of large roof overhangs at reentrant corners or landings should

be avoided in a severe wind environment. This

restriction is necessary because these elements are highly susceptible to impact by flying debris and

uplift transmitted from the roof.

5. Large roof overhangs serve as vehicles for attract- ing and transmitting higher uplift forces to the system and therefore require more substantial construction provisions against high winds. Considerations such as aesthetics, shading provisions

and social preferences of dwelling environment

should be traded off against practicability of design and increased costs associated with such

practices to arrive at a reasonable compromise.

6. Overall integrity of the system should be assured by providing continuity between vertical wall reinforcement and the roof and foundation

through appropriate utilization of reinforcing bars and anchor bolts and by providing continuity

between intersecting walls by means of tiebars and/or horizontal reinforcement grouted within a bond beam course and extending into the neighboring walls and partitions.

7. The use of infill wall construction in building

systems under a severe wind environment should

be encouraged. The masonry infill walls should be

laid first on top of a cast concrete wall footing and

12
attached to it by means of dowels lapped a suffi- cient distance with the vertical reinforcement

placed into the grouted cores of the hollow blocks. Horizontal and vertical reinforcement should

project from the sides and top of the filler walls to achieve continuity with the surrounding concrete frame which should be cast last.

8 > 8 X 16 STANDAR D

8 X 8 « 16 SASH

Length Conversion

1 in - 25.4 mm

lin = 0.0254 m

SASH

8x8x8 8x8x8 8x8x16

SASH LINTEL STANDARD LINTEL BOND BEAM

6x8x16 6x8x14 6x8x16

CHANNEL CORNER OFFSET CORNER

4x8x16 4x8x8 4x8x12

STANDARD HALF CORNER

FIGURE 6 CONCRETE MASONRY UNITS.

13
FIGURE 8 COLLAPSE OF ONE-STORY BUILDING

CAUSED BY THE NOVEMBER 1974

TYPHOON IN THE PHILIPPINES.

24
FIGURE 9 FAILURE OF METAL ANCHOR

PLATE IN BUILDING

DESTROYED BY NOVEMBER

1974 TYPHOON IN THE

PHILIPPINES.

FIGURE 10 ROOF FAILURE IN BUILDING CAUSED BY NOVEMBER 1974 TYPHOON IN

THE PHILIPPINES.

15
FIGURE 11 SINGLE FAMILY HOUSES DAMAGED OR DESTROYED BY TYPHOON IN

NOVEMBER 1970, IN CENTRAL LUZON, THE PHILIPPINES.

FIGURE 12 SINGLE FAMILY HOUSE

SHOWING COLLAPSE OF ROOF

AND EXTERIOR WALL DURING

THE PHILLIPINES TYPHOON

IN NOVEMBER 1970.

16
17
FIGURE 15 BUILDING OF CAVITY WALL

CONSTRUCTION IN DARWIN,

AUSTRALIA, PARTIALLY

DESTROYED BY THE

DECEMBER 1974 CYCLONE.

FIGURE 16 BUILDING IN DARWIN, AUSTRALIA SHOWING PARTIAL COLLAPSE OF

ROOF AND MASONRY INFILL WALLS CAUSED BY THE DECEMBER 1974

CYCLONE.

18
FIGURE 17 FAILURE OF CONCRETE BLOCK MASONRY WALL IN BUILDING

SUBJECTED TO THE DECEMBER 1974 CYCLONE IN DARWIN, AUSTRALIA.

FIGURE 18 SINGLE FAMILY MASONRY HOUSE UNDER CONSTRUCTION IN CENTRAL

LUZON, THE PHILIPPINES.
FIGURE 19 STACKED BOND CONCRETE MASONRY WALL CONSTRUCTION FOR

SINGLE FAMILY OCCUPANCY IN CENTRAL LUZON, THE PHILIPPINES.

FIGURE 20 SINGLE FAMILY HOUSING DEVELOPMENT IN CENTRAL LUZON, THE

PHILIPPINES.
21
*

FIGURE 23 REINFORCED CONCRETE MASONRY DWELLING UNIT IN CENTRAL

LUZON, THE PHILIPPINES.

FIGURE 24 REINFORCED CONCRETE MASONRY WALLS UNDER CONSTRUCTION FOR

HOUSING IN CENTRAL LUZON, THE PHILIPPINES.

22
FIGURE 25 CONCRETE MASONRY BEARING

WALL CONSTRUCTION WITH

TRUSS TYPE ROOF FOR

HOUSING IN CENTRAL LUZON,

THE PHILIPPINES.

FIGURE 26 SINGLE FAMILY HOUSING

UNDER CONSTRUCTION IN

CENTRAL LUZON, THE

PHILIPPINES, SHOWING

CONCRETE BOND BEAM DETAIL

OVER OPENINGS.

23
FIGURE 27 CARE SPONSORED HOUSING PROJECT NEAR DACCA, BANGALADESH

SHOWING CINVA-RAM WALL CONSTRUCTION WITH CORRUGATED

METAL ROOFING.

(h) FIGURE 28 VARIOUS METAL ANCHORS: (a), (b) TIEBARS WITH END HOOKS; (c) TIEBAR

WITH HOOK AND SPLIT HOOK; (d) TIE BAR WITH 90° TWIST: (e) CORRUGATED DOVETAIL TIE; (f ) CORRUGATED TIE; (g) DOVETAIL TIE

WITH HOOK;(h) ANCHOR BOLT.

24
Cross bracing at every wall anchor and at intermediate spacings as required.

(a)

Floor or

roof joists or beams.

Nail anchors to underside or

side o( loists.

Wall anchors at required intervals

,

Anchors should have split end embedded m mortar joint or end bent down into block core and core filled with mortar. Length of anchor should be sufficient to engage at least three loists.

(b)

Solid unit

Hollow bridging unit

Solid top units m

course supporting

floor joists.

Wood joisls fran- into masonry wall. Joists to have min. 3" bearing on masonry.

I'A'x'/s" twisted steel plate anchors with one end embedded

in horizontal mortar joint.

(c)

Place melal lalh or wire screen over cores to support mortar or concrete (ill.

Rake out and

caulk to form

control joint if exposed to view.

1'/4"k'/4"x30' strap anchors with 3" right angle bends at each

end, al vertical spacings not exceeding 32" o.c.

Embed beni ends

in cores filled with mortar or concrete.

FIGURE 29 APPLICATION OF METAL ANCHORS IN MASONRY CONSTRUCTION: (a) TIEBAR ANCHOR TO WOOD JOISTS; (b) TWISTED ANCHOR CONNECTING

WOOD JOIST TO CONCRETE MASONRY BEARING WALL; (c) TIEBAR

ANCHOR CONNECTING CONCRETE MASONRY INTERSECTING WALLS.

Length Conversion

1 in = 25.4 mm

1 in = 0.0254 m

Toenail joist to

sill or anchor to

Trip-L-Grip or

similar anchors

as shown.

Fill hollow cores in course

supporting floor with concrete

or mortar.

1/2" min, dia. anchor bolts extending al least 15" into

filled cells m the masonry

and spaced not more

than 6'-0" o.c. to anchor sill to wall.

Place wire screen or metal lath ii joint under cores to be filled to prevent filling of cores below.

Rake out and caulk Metal washer 3

Double studs

Vz" bolts top and

bottom courses and 32" o.c. max.

WOOD STUD WALL

(a) (b)

FIGURE 30 APPLICATION OF ANCHOR BOLT FOR MASONRY CONNECTION: (a) CONNECTION OF SILL PLATE TO CONCRETE MASONRY BEARING WALL;

(b) CONNECTION OF CONCRETE MASONRY WALL TO WOOD STUD WALL.

25
(d) (e)

FIGURE 31 JOINT REINFORCEMENT IN MASONRY WALLS: (a) TRUSS; (b) LADDER; (c) AND (d) PREFABRICATED CORNER SECTION; (e) AND (f) PREFABRICATED

TEE SECTION.

Length Conversion

1 in = 25.4 mm

1 in = 0.0254 m

'/a" round ties

in mortar joint

Va" round ties around vertical bars

(a) (b)

Outside bars extend around

corner - inside bars extend as far as possible & bend into corner core

EXTERIOR WALL BOND BEAM BOND BEAM

AT WALL INTERSECTION

(c) (d)

FIGURE 32 HORIZONTAL REINFORCEMENT BETWEEN INTERSECTING MASONRY

WALLS: (a) AND (b) WITHOUT BOND BEAMS; (c) AND (d) WITH BOND BEAM

Facing Page: Roof Structural system in a new United

States - Republic of Philippines School Building.

26
3. FASTENERS FOR TIMBER

CONSTRUCTION IN HIGH

WIND AREAS

by

G.E. Sherwood and T.L. Wilkinson *

3.1 INTRODUCTION

Houses and other low-rise buildings in many tropical areas such as Jamaica, Bangladesh, and the Philip-

''Messrs G.E. Sherwood and T.L. Wilkinson are engineers with the Forest Products Laboratory, Forest Service, U.S. Department of Agriculture, maintained at Madison, Wisconsin, in cooperation with the University of Wisconsin.

pines are subject to extreme winds several times each

year. Failures that occur in buildings or building ele- ments of wood construction usually occur in the

fasteners rather than in the structural members.

Buildings that are adequately braced to resist racking

forces, and have each element tied together from

foundation to roofing, can resist high winds without

structural failures. This section describes and provides

27
sources for commercially available timber connectors,

existing timber-related building practice in the Philippines, and identification of good and poor timber connector practice. It also presents recommended practice, including connectors that can be fabricated by the indigenous people.

3.2 AVAILABLE TIMBER FASTENERS

3.2.1 Nails, Screws, Bolts, and Lag Screws

These common mechanical fasteners for wood come

in many varieties. A variety of nails is shown in figure 33. Some may be used for several purposes while others are intended for special purposes.

In general, nails resist or transmit smaller loads than

screws, and screws resist or transmit smaller loads than bolts or tag screws. However, because of their smaller size, more nails can usually be used in a joint. A good source of information on the design of joints

with such fasteners is the National Design Specification

for Stress-Grade Lumber and Its Fasteningsby the National Forest Products Association [47]. There are a large number of manufacturers of such

fasteners. The best source for obtaining names of manufacturers in the Thomas Register of American

Manufacturers and Catalog File [26\.

These manufacturers can provide catalogs which

describe the fasteners they manufacture along with

the intended purpose for each.

3.2.2 Timber Connectors

Timber connectors generally refer to split rings, shear

plates, and toothed rings (figs. 34, 35, and 36). These are intended primarily for heavy [members larger than

100 mm (4 in) thickness) construction and usually

result in bulky joints. Special tools and skills are needed for properly constructed timber connector

joints.

Split rings and toothed rings are used for wood-towood joints, and shear plates are used for wood-tosteel joints, and sometimes for wood-to- wood joints.

Proper joint design procedures and loads can be found

inref. [47].

Manufacturers of timber connectors as listed in Thomas Register are as follows:

(1) Simpson Company

1472 Doolittle Drive

San Leandro, California 94577

(2) Woodmack Products, Inc. 852 Aldo Avenue

Santa Clara, California 95050

(3) Timber Engineering Company

5530 Wisconsin Avenue

Washington, D.C. 20015

(4) Kees, F.D., Manufacturing Company

21 High Street

Beatrice, Nebraska 68310

(5) Cleveland Steel Specialty Company

14442 Industrial Avenue,

South Cleveland, Ohio 43228

3.2.3 Truss Plates

These fasteners are made of galvanized sheet metal,

usually 20 gage, intended primarily for use as gussets

for light timber [members 50 mm (2 in) thick] trusses, the plates may be obtained in many sizes of rectangular shape. Their means of transferring load vary from

the use of nails in punched holes, plugs or barbs of

different shapes, to teeth of different shapes and

lengths. Figure 37 shows some typical plates.

Procedures for designing with these plates are pre- sented in Design Specifications for Light Metal Plate Connected Wood Trasses by the Truss Plate Institue [48]. This publication also lists 11 manufacturers which are members of the Truss Plate Institute.

Detailed description of the plates and design loads can

be obtained from the manufacturers.

3.2.4 Sheet Metal Fasteners and Other Special

Devices

These fasteners include such items as joist and beam

hangers, framing anchors, rafter anchors, post

anchors, etc. (fig. 38), which are made of galvanized

sheet metal and which require fastening to the framing with nails or screws. A good reference for descriptions and specifications

of these fasteners is Products in Actionhy the Timber

Engineering Company [49]. Some of the manufacturers of truss plates also make

certain types of special fasteners for use in framing

applications.

3.3 PHILIPPINE TIMBER-RELATED

PRACTICES

Timber-related building practices in the Philippines can be divided into three general categories:

(1) Pole-type construction in which poles are set into the ground to serve as foundation and ex- tend to the roof (fig. 39).

28
(2) Concrete slab, perimeter, or pier foundation of concrete or masonry with wall and roof framing of wood (fig. 40).

(3) Concrete slab or perimeter foundation supporting masonry or cast concrete walls, and a wood-frame roof (fig. 41).

3.3.1 Pole Type

This type of construction is well suited to high wind

areas because the major structural member, the pole, serves as the connecting link between all other structural members. If the poles are set 1.2 m (4 ft) or more

into the ground, they serve as anchors for the building. For long life, all poles must be pressure treated for resistance to decay and insect attack. Roof framing members are either round or sawn timbers. In remote areas, they may be tied together with

strips of bamboo (fig. 42). This type of connector appears to provide good resistance to wind forces. Nailing is also effective if nails are loaded laterally rather than in direct withdrawal.

Covering materials for this type of construction are

often thatch roofs and walls of thatch or bamboo.

There appears to be no way to assure anchorage of thatch during high winds V fig. 33). Wood siding

nailed to framing members offers good resistance to wind, but nails should be corrosion resistant.

3.3.2 Wood-Framed Wall and Roof

Wood-framed walls often have a single covering

material. It may be applied to the exterior of the building or set between framing members. Anchor

bolts are used to tie the wall to the foundation. Where

the foundation is concrete block, the anchor bolt should extend through blocks into the footing. If the house is anchored only to the top concrete block, this block may be pulled from the foundation and moved

with the house.

Covering material applied on the outside of the framing (fig. 44) protects the wall framing and connectors from rain. Walls with the covermg set into the framing have a greater potential for trapping water, and

thus promoting decay. Anchor bolts on the outside of

the wall are particularly susceptible to trapping water

(fig. 45). They can easily be placed on the inside for protection. The type of sill plate shown in figure 45

also traps water. The sill plate should at least be sloped to the outside so water will drain from it, and

the joint with panel materials should be caulked.

Roof framing is either nailed to the top of the wall or secured with sheet metal connectors. Good nailing

should hold down the roof framing, but sheet metal

connectors provide a stronger joint and have less chance of being improperly nailed.

3.3.3 Masonry Wall

One method of tying roof framing to a masonry wall

is to cast reinforced concrete columns at all corners and at intermediate locations on long walls. Reinforcement is tied to the foundation and extends above

the columns so that it can be attached to a wood beam

which extends completely around the perimeter of the house on top of the masonry wall. Trusses are sometimes anchored to this beam by metal straps nailed to both members. The metal strap has a 90°

twist at its center which weakens it and allows the

nails to be pulled out when anything but a direct

uplift force is exerted on the strap (fig. 46). A sheet metal connector that can be nailed to both

sides of the rafter and beam would prevent the type of

failure caused by rotation in the single, heavy strap.

3.3.4 Roof Framing

Framing for the roof of any of the types of structures involves use of either trusses or a rafter-and-joist

system. Trusses are fabricated with metal plate connectors or bolted joints. In some larger structures,

split-ring connectors are used. Trusses generally are made from an engineered design and under controlled conditions, so they have less potential for failure than the conventional rafter-and-joist system.

Where rafters are used, some type of collar tie is important to keep the roof from dividing at the peak

(fig. 47). Ceiling joists, well nailed or bolted to rafters, prevent the roof from spreading outward (fig. 48). Purlins are connected to rafters or trusses in several ways. Nailed joints are among the most vulnerable

because in this application the nail is loaded in direct withdrawal. Short boards 50 by 50 mm (2 by 2 in) nailed to the purlin and the rafter (fig. 48) provide a stronger joint by loading the nails laterally.

3.3.5 Roofing

The major roofing material in the Philippines is cor- rugated sheet metal. One method of tying roofing to purlins is the use of sheet metal straps (fig. 49). One

end of the strap is bent at a 90° angle, and the bent

portion is riveted to the roofing. The strap is nailed to the side of the purlin and bent under the purlin. The

attachment of the strap to only one side of the purlins

results in an unsymmetrical load so the strap can be

twisted off by wind forces. Two straps riveted to the roofing on both sides of the purlin and lapped under

the purlin, would resist forces due to moment in the connector.

Figure 50 illustrates the effectiveness of having

tiedowns symmetrically loaded. A wire was tied to a nail in the bottom of the purlin, punched through the

29
roofing, wrapped over the purlin, and tied back to the

nail. This tie held well enough that the purlin-torafter connection failed before the roofing connector. However, roof leakage may be a problem.

3.3.6 Protection From Wood-Destroying

Organisms

A key element of good performance of timber connectors is maintenance of the strength properties of the wood. In many cases where failures have occurred, some deterioration of the wood is evident (fig. 51). Staining is prevalent around many nails and bolts(fig.

52), which reduces decay resistance of the wood. Corrosion of nails also results in loss of cross section which loosens the nails. In such a humid environment, all connectors should be corrosion resistant.

3.3.7 Summary of Good and Poor Practices

Design, construction, and maintenance practices are summarized below:

1 . Design the building to act as a unit by connecting

all components together and anchoring the whole structure to the foundation. Design joints

to resist torsion as well as uplift even where it means using connectors in pairs.

2. The use of engineered trusses fabricated under

good quality con.trol assures structural integrity of the roof framing. Where trusses are not used, collar beams and ceiling joists must be nailed or bolted to the rafters. Sheet metal connectors pro- vide better quality control at joints than nails alone.

3. Pole framing offers a good way of tying components together because all major structural members are connected to the poles. In masonry construction, a reinforcing rod extending from the footing to the roof provides the required continuous tie.

4. All connectors should be corrosion resistant. Locate connectors where they are protected from

rain, and avoid exposed joints which trap water.

5. Loads should not be concentrated in a small number of connectors. Connectors applied to only one

side of a member can often be twisted off because

they have little resistance to torsional loads.

6. Nails loaded in direct withdrawal offer less resis- tance than laterally loaded nails. Roof framing

that is anchored only to the top course of a block

wall may blow off taking the blocks with it.

7. The use of connectors that are not corrosion resist- ant is poor practice in a humid location. Exposure

of connectors to rain provides a place for water to enter the wood and promote decay. Horizontal

members exposed as exterior elements form water

traps which can lead to decay.

3.4 TIMBER FASTENERS APPROPRIATE FOR

CONSTRUCTION IN DEVELOPING

AREAS WITH HIGH WINDS

3.4.1 Pole-Type Construction

Where poles are set in the ground to serve as the main

vertical framing, major floor and roof framing

securely attached to the poles assures the structural in- tegrity of the building. Round framing members com- monly used for indigenous type of construction have

been successfully tied to the poles with strips of bamboo (fig. 3). Sawn timbers should be bolted to the poles

using 19-mm (3/4-in) or larger bolts, depending on the

load. If round poles are used with sawn timber framing, notching the pole to provide a wider bearing sur- face (fig. 53) may be necessary, especially where two

members meet end-to-end (fig. 54).

Siding materials may be boards nailed directly to the framing. Corrosion-resistant nails are particularly important for this application. Indigenous-type construction often employs walls of bamboo or thatch. These coverings have served well in many applications, but are difficult to secure in extreme winds.

3.4.2 Light Wood-Frame Construction

The wood-frame must not only be anchored to the foundation at its base, but must also provide a continuous tie from the foundation to the roof. Anchorage of wall framing to a concrete foundation

may be accomplished with hooked bolts embedded

0.2 to 0.3 m (8 to 12 in) in the concrete. A large washer

should be used under the nut to spread the load on the wood framing (fig. 55). Where the foundation is concrete block, the anchor bolt should extend through the block and be anchored in the concrete footing (fig. 56). The exposed end of the anchor bolt should be protected from weather. Where a single covering

material is set into framing, the bolt should be placed on the protected side of the covering material (fig. 57). The wall must be tied together as well as anchored.

Panel-type covering material nailed to the anchored

sill and to the top plate provides this continuous tie. Panel material nailed to framing completely around

its perimeter also provides racking resistance in the

wall. Where siding does not provide such a tie, sheet metal straps can be used as connectors between plates

and vertical framing (fig. 58). Roof framing is effectively tied to walls with sheet metal brackets (fig. 59) or wood cleats (fig. 60). Where

30
a ceiling joist-and-rafter system is used, sheet metal

straps nailed to joists and studs (fig. 61) provide a good

tiedown for roof framing. In this method, the rafter must be well nailed to the ceiling joists.

3.4.3 Concrete and Masonry Construction

Cast concrete posts at corners and intermediate loca- tions in concrete block walls provide tiedown points

for roof framing. Wood plates can be tied down to hooked bolts in the cast concrete posts or walls. This is the same type of connector shown in figure 55. Roof

framing can then be attached to the anchored plate by

sheet-metal brackets or wood cleats as shown in figures 59 and 60.

3.4.4 Roof Framing

Trusses may be used for roof framing for any of the types of construction that have been discussed. Connectors may be metal plates for light construction or

split-rings for heavy construction. Split-rings that are tapered in cross section and wedged into place have

the highest load-carrying capacity.

3.4.5 Roofing

Thatch roofs are often used for indigenous construction. The thatch is tied to small poles which are laid on the roof in courses with each course overlapping

the one below. Poles are secured by tying them to roof framing with bamboo strips which provide good

resistance to wind loads. However, the thatch itself may blow off in extreme winds.

The predominant roofing material is corrugated,

galvanized sheet metal. The usual roof system consists of purlins (sometimes referred to as roof joists) span- ning between rafters or trusses, and roofing attached

to these purlins. The purlins should be tied to rafters with sheet metal brackets (fig. 62) or with wood cleats

(fig. 63). In either case the tiedowns should be attachable to both sides of the purlin and rafter, so they cannot be twisted off by loads that are not perpendicular

to the purlins.

Corrugated roofing is best affixed by a fastener that wraps completely around the purlin. Two sheet metal

straps lapped under the purlin and riveted to the cor- rugated roofing on each side of the purlin (fig. 64) provide a good connector system that will resist moment loads which cause failure when a strap is used on only one side.

3.5 FASTENERS FOR FABRICATION BY

INDIGENOUS PEOPLE

Any of the sheet metal straps could be easily fabri- cated with a minimum of tools. A minimum thickness

of 20-gage galvanized sheet metal should be used. A

width of 32-mm (1-1/4 in) and a length of 0.5 m (20 in) would be suitable for many applications (fig. 65). It may be necessary to vary this size for specific applications.

Galvanized straps could be fabricated for roofing

tiedowns. This strap should be only about 152 mm (6

in) long, bent at 90°, 25-mm (1-in) from one end, and

have a 6-mm (1/4-in) hole punched in the 25 mm (1- in) section (fig. 66). These straps should be used only in pairs on opposite sides of a purlin. The ends of the

straps should be bent under the purlin with the two

straps lapped and nailed to the bottom as well as sides of the purlin.

A multipurpose bracket could be fabricated from 20- gage galvanized steel. A suggested size is given in figure 67; however, this could be varied for other standard sizes of wood framing. Slits cut in the sheet metal permit forming the bracket for a variety of uses.

Split-ring connectors have been fabricated by cutting

19-mm (3/4-in) wide sections from 76-mm (3-in) steel pipe, and then cutting the ring at an angle. This connector and present commercially produced split-ring connectors are shown in figure 68. For maximum

strength the ring should be wedged tightly into the

circular groove cut in the wood. Present commercial

split-rings cut from steel pipe should have good load- carrying capacity even though its capacity would be

somewhat less than the tapered ring.

Metal plate connectors for truss joints is another

possiblity for fabrication by indigenous people. These

are usually fabricated from 20-gage galvanized sheet

metal. The sheet metal is punched in a way that pro- duces barbs or teeth at right angles to the plate. Plates with barbs punched in the pattern shown in figure 69

generally do not maintain optimum strength after ex- pansion and contraction of the wood with moisture

changes over a long period of time. Plates with teeth that penetrate deeper than barbs are less affected by

moisture cycling of the wood.

3.6 SUMMARY

Wind-resistant construction for wood-frame build- ings in developing countries can be achieved by pro- viding good connectors between all members from

foundation to roofing. All connectors should be corro- sion resistant and protected from rain where possible. Connectors should be designed to resist being twisted

off. Where nails are used, connectors should be a type

that load the nails laterally rather than in direct withdrawal.

Sheet metal straps and brackets could easily be fabri- cated by indigenous people in developing countries. Such connectors could be fabricated using a minimum

of tools and equipment.

31
3.7 A CAUTION

In present tropical construction, the most frequent

failure caused by high winds is the loss of roofs. It should be recognized that improved design which

holds the roof securely will ultimately result in the

concentration of greater loads in other parts of the

building. Details of wall construction and anchorage

to the foundation which have been adequate when

the roof failure relieved the total load on the building,

may not be adequate when the roof remains intact. The building will be subjected to a large overturning

moment as well as to uplift load on walls.

FIGURE 33 VARIOUS TYPES OF

NAILS: (a) BRIGHT, SMOOTH

WIRE NAIL; (b) CEMENTCOATED; (c) ZINC-COATED;

(d) CHEMICALLY ETCHED;

(e) ANNULARLY THREADED;

(£) HELICALLY TREADED;

(g) HELICALLY THREADED

AND BARBED; AND

(h) BARBED. ABC D E F G

FIGURE 34 JOINT WITH SPLITRING CONNECTOR

SHOWING CONNECTOR,

PRECUT GROOVE, BOLT,

WASHER, AND NUT.

32
FIGURE 35 JOINT WITH

TOOTHED-RING

CONNECTOR.

FIGURE 36 JOINTS WITH SHEAR-PLATE

CONNECTORS WITH (a) WOOD SIDE PLATES; AND

(b) STEEL SIDE PLATES.

33
FIGURE 37 SOME TYPICAL TRUSS PLATES.

TECO DU-AL-CLIP

Framing Anchors

FIGURE 38 SOME EXAMPLES OF SPECIAL FASTENERS.

34
FIGURE 39 POLE-TYPE CONSTRUCTION.

FIGURE 40 WOOD-FRAME WALL AND ROOF.
FIGURE 41 CONCRETE BLOCK WALL WITH WOOD FRAME ROOF.

FIGURE 42 ROOF FRAMING TIED DOWN WITH STRIPS OF BAMBOO.

36
FIGURE 43 THATCH ROOF WITH THATCH

PARTIALLY BLOWN OFF.

FIGURE 44 COVERING MATERIAL ON THE

OUTSIDE PROTECTS FRAMING

AND CONNECTORS.
FIGURE 45 ANCHOR BOLT AND SILL PLATE EXPOSED TO WEATHER PRESENT DECAY

HAZARDS.

FIGURE 46 METAL STRAP ON ONLY ONE SIDE OF FRAMING FAILED TO RESIST

BENDING LOAD.

38
FIGURE 47 COLLAR TIES HOLD RAFTERS FROM PULLING APART AT THE PEAK.

FIGURE 48 CEILING JOIST BOLTED TO RAFTERS RESISTS OUTWARD THRUST OF

RAFTER; WOOD CLEATS TIE PURLINS TO RAFTERS.

39
FIGURE 49 SHEET METAL STRAP NAILED TO ONE SIDE OF PURLIN AND RIVETED TO

CORRUGATED ROOFING.

FIGURE 50 ALTHOUGH THE ROOF BLEW OFF OF THE STRUCTURE, THE

CORRUGATED ROOFING WAS EFFECTIVELY TIED TO PURLINS BY WIRES

COMPLETELY AROUND THE PURLINS.
FIGURE 51 JOINT FAILURE DUE TO DECAY IN WOOD.

FIGURE 52 STAINING FROM CORROSION OF BOLTS AND NAILS.

41
FIGURE 53 ROUND POLE NOTCHED

FOR SAWN FRAMING

MEMBER.

FIGURE 54 TWO FRAMING MEMBERS

BUTTED END-TO-END OVER

FLAT NOTCH AND

BOLTED TO A POLE.

'^^^^ CONCRETE BLOCKS

WASHER

SOLE PLATE

HEADER PLATE

ANCHOR BOLT

GROUT CORES WITH ANCHORS

^CONCRETE FOOTING

FIGURE 55 ANCHOR BOLT IN CONCRETE A

MINIMUM OF 0.2 m (8 in); WASHER

TO SPREAD LOAD.

.WASHER

^X^^SOLE ^^^;^^1^S0LE PLfiLATE

A

VV

FIGURE 56 ANCHOR BOLT THROUGH

CONCRETE BLOCK FOUNDATION

INTO FOOTING.

42
FIGURES? ANCHOR BOLT INSTALLED FIGURE 58 SHEET METAL STRAP

ON PROTECTED SIDE TYING STUD TO

OF WALL. BOTTOM PLATE.

ROOF FRAMING

METAL BRACKET

DOUBLE TOP PLATES

STUD

FIGURE 59 SHEET METAL BRACKET FOR TYING

ROOF FRAMING TO WALLS.

43
FIGURE 62 SHEET METAL FIGURE 63 PURLINS TIED TO RAFTERS

BRACKET USED TO BY WOOD CLEATS.

CONNECT PURLIN

TO RAFTER.

STRAPS LAPPED UNDER

PURLIN AND NAILED

FIGURE 64 TWO METAL STRAPS RIVETED TO

CORRUGATED ROOFING, LAPPED

UNDER PURLIN AND NAILED

TO PURLIN.

44
20 -GAGE GALVANIZED

SHEET METAL

1/4"

20"

FIGURE 65 MULTI-PURPOSE STRAP; LENGTH

AND WIDTH CAN BE VARIED FOR

SPECIFIC APPLICATIONS.

FIGURE 66 GALVANIZED SHEET METAL

STRAP WITH RIVET AND

WASHER FOR TYING DOWN

CORRUGATED ROOFING.

Length Conversion

1 in = 2S.4 mm

1 in = ().()254m

BEND LINES

1/2

11/2'

TI 1/2*

11/2 4 5/8'

4 5/8*

FIGURE 67 MULTI-PURPOSE BRACKET FABRICATED FROM

20-GAGE GALVANIZED STEEL; BEND EITHER

DIRECTION AT BEND LINES TO FORM DESIRED

BRACKET.

45
SPLIT-RING CONNECTOR FOR INDIGENOUS FABRICATION (LEFT), AND

COMMERCIALLY PRODUCED SPLIT-RING CONNECTOR (RIGHT).

FIGURE 69 PLATE CONNECTOR WITH BARBS.

46
REFERENCES

(1) Raufaste, N.J., and Marshall, R. D., FY 74 Progress Report

on Design Criteria and Methodology for Construction of Low-Rise Buildings to Resist Typhoons and Hurricanes, NBSIR 74-567 (Washington, D.C.: National Bureau of Standards, July 1, 1974).

(2) Reps W.F., and Simiu, E., editors. Design, Siting, and

Construction of Low-Cost Housing and Community Buildings

to Better Withstand Earthquakes and Windstorms. BSS-48 (Washington, D.C.: National Bureau of Standards,

January 1974).

(3) Sweet's Industrial Construction Catalog File (New York:

Sweet's Division, McGraw-Hill Information Systems

Company, n.d.). (4) Standard for Mobile Homes, ANSI Al 19.1-1974, and Appendix D, ANSI Al 19. 1-1975 (New York; American

National Standards Institute, 1974).

(5) Protecting Mobile Homes from High Winds, TR-75

(Baltimore: Defense Civil Preparedness Agency,

Department of Defense, 1972).

(6) Nara janamurty, D., and Mohan, D., The Use of Bamboo

and Reeds in Building Construction, no. E.72, IV. 3(New

York: United Nations, n.d.).

(7) Pole House Construction {McLean: American Wood

Preservers Institute, 1971).

(8) Concrete Masonry Design ManualiLos Angeles: Concrete

Association, 1955).

(9) ASTM Standards iPh'\lade\ph'\a: American Society for Testing and Materials, n.d.). (10) Raufaste, N.J., and Marshall, R.D., FY 1973 Progress Report on Design Criteria and Methodology for Construction

of Low-Rise Buildings to Better Resist Typhoons and

Hurricanes, NBSIR 74-582 (Washington, D.C.: National Bureau of Standards, 1973).

(11) Raufaste, N.J., and Marshall, R.D., editors. Development

of Improved Design Criteria for Low-R isc Buildings in Developing Countries to Better Resist the Effects of Extreme

Winds, BSS 56 (Washington, D.C.: National Bureau of Standards, 1974).

(12) Housing and Urban Development in the Philippines {ManWa:

USAID Mission, 1968).

(13) "Amendment No. 1 to Specification for Portland Cement," Philippine Trade Standard 661-01.02: 1972

(Manila: Bureau of Standards, 1972).

(14) "Specification for Portland Cement," Philippine Trade

Standard 661 -01.02 {Mam\a: Bureau of Standards, 1968). (15) "Standard Specification for Glazed Ceramic Tiles and

Tile Fittings,"PH/LSA /- 7 0-72 (Quezon City: Philippine Standards Association, 1972).

(16) "Standard Specification for Philippine Cold Drawn Steel Wire for Concrete Reinforcement," PHILSA 1-5-71 (Quezon City: Philippine Standards Association, 1972). (17) "Standard Specifications for Steel Reinforcement Bar," PHUSA 1-7-71, (Quezon City: Philippine Standards

Association, 1975).

(18) "Standard Specifications for Construction Lime," PHILSA /-7-68(Manila: Philippine Standards

Association, 1968).

(19) "Masonry", PACE CP 206 (Manila: Philippine

Association of Civil Engineers, 1965).

(20) "Private Practice of Structural Engineering," Manual of Engineering Practice No. 7 (Quezon City: Association of

Structural Engineers of the Philippines, 1973).

(21) "Private Practice of Civil Engineering," PACE Mfl^iua/ o/ Engineering Practice No. 7 (Manila: Philippine

Association of Civil Engineers, 1960).

(22) "Code of Practice for the Design, Fabrication and

Erection of Structural Steel Members with Minimum

Thickness of 1/8" for Buildings," PACE CP205(Manila:

Philippine Association of Civil Engineers, 1968).

(23) "Engineering Standards," PACE CP 200(Manila:

Philippine Association of Civil Engineers, 1965). (24) "Excavations and Foundations," PACE CP207 (Manila:

Philippine Association of Civil Engineers, 1965).

(25) National Structural Code of Buildings(Man\\a. Philippine

Association of Civil Engineers, 1972).

(26) Thomas Register of American Manufacturers and Catalog

File(New York: Thomas Publishing Company, n.d.). (27) Proceedings of Conference on Unified Building Code

(Kingston: Caribbean Council of Engineering

Organizations, n.d.). (28) Specification for the Design and Construction of Load- BearingConcrete Masonry( Arlington: National Concrete Masonry Association (NCMA), n.d.). (29) Research Data with Commentary in Support of Specification

for the Design and Construction of Load-Bearing Concrete Mflso«ry(Arlington: National Concrete Masonry

Association, n.d.). (30) Report on Concrete Masonry Structures-Design and

Construction, ACl Committee 531( American Concrete

Institute Journal, 1970).

(31) American Standard Building Code Requirements for Masonry, ANSI A41, Miscellaneous Publication 211 (Washington, D.C.: National Bureau of Standards, 1954).

(32) Uniform Building Code (Whittier: International Conference

of Building Officials, 1973).

(33) Toennies, El., and Merteu, John, E., Concrete Masonry

Vocationa I Tra in ing S tuden ts'Mfl«Mfl/(Arlington: National Concrete Masonry Association, n.d.). (34) NCMA TEK Series (Arlington: National Concrete Masonry

Association, n.d.). (35) Yokel, F.Y., Mathey, R.G., and Dikkers, R.D., Compressive Strength of Slender Concrete Masonry Walls, BS 33 (Washington, D.C.: National Bureau of ^^a idards,

1970). (36) . Yokel, F.Y., Mathey, R.G., and Dikkers, R.D., Strength of Masonry Walls Under Compression and Transverse Loads, BSS 34 (Washington, D.C.: National Bureau of Standards, 1971).

(37) Yokel, F.Y., and Dikkers, R.D., "Strength of LoadBearing Masonry Walls," Journal of the Structural Division (New York: American Society of Civil Engineers, May

1971) . (38) Yokel, F.Y., "Stability and Load Capacity of Members

with No Tensile Strength," Journal of the Structural Division(New York: American Society of Civil Engineers, July 1971).

(39) Fishburn, C, E//ecf of Mortar Properties on Strength of Masonry, NBS Monograph 36 (Washington, D.C.: National Bureau of Standards, 1961).

(40) Dikkers, R.D., and Saxer, E.L., Flexural Strength of Plain and Reinforced Concrete Masonry Wfl//s( Arlington: National Concrete Masonry Association, 1957).

(41) Livingston, A.R., Mangotich, E., and Dikkers, R.D., Flexural Strength of Hollow Unit Concrete Masonry Walls,

in the Horizontal Spfln( Arlington: National Concrete Masonry Association, 1958).

(42) Moss, P. J., and Scrivener, J.C., "Concrete Masonry Wall

Panel Tests, New Zealand Concrete Construction,"

Journal of the New Zealand Portland Cement Association (New Zealand Portland Cement Association, 1968).

(43) Scrivener, J.C., "Static Racking Tests on Concrete Masonry Walls" (International Conference on Masonry

Structural Systems) (Austin: n.p., 1967).

(44) Amrhein, J.E., Reinforced Masonry Engineering Handbook

(Los Angeles: Masonry Institute of America, 1972).

(45) Amrhein, J.E., Masonry Design Manual (Masonry

Industry Advancement Committee, 1972).

(46) Schneider, R.R., Shear in Concrete Masonry Piers(Los Angeles: Masonry Research of Los Ageles, 1969).

47
(47) National Design Specifications for Stress-Grade Lumber and

Its Fastenings (Washington, DC: National Forest Products Association, 1973).

(48) Design Specifications for Light Metal Plate Connected Wood

Trusses (College Park: Truss Plate Institute, n.dj.

(49) Products m Action (Washington, D.C.: Timber

Engineering Company, n.ci.).

ACKNOWLEDGMENTS

The contributions of the following persons are acknowledged:

Noel Raufaste, jr.. Center for Building Technology, for supplying field survey documentation and for cri- tically reviewing the report.

Deborah Borkman, Cathy Warfield, and julie Reinhold, Center for Building Technology, for typing the manuscript.

Thomas Ruschell and Loins Cattaneo, Center for Build- ing Technology, for organizing and proofreading the

report.

Ricardo Florez, Guest Worker, Center for Building

Technology, for his assistance in preparing figures

and for his constructive suggestions.

Stephen Kliment, AIA, New York City, for supplying

those figures and references relating to pole type construction.

Charles Yancey, Center for Building Technology, for critically reviewing the report.

Charles Raley, Office of International Relations, for critically reviewing the report.

48
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