P.1-i

Table of Contents

Basic Concepts 

Primer ..................................................................................................................................................

 

 P.1 Bridge Components and Elements.........................................................P.1.1 

 P.1.1 Introduction...............................................................................P.1.1 

 P.1.2 NBIS Structure Length..............................................................P.1.1 

 P.1.3 Major Bridge Components........................................................P.1.1 

 P.1.4 Basic Member Shapes...............................................................P.1.2 

 Timber Shapes....................................................................P.1.2 

 Planks...........................................................................P.1.3 

 Beams...........................................................................P.1.3 

 Piles..............................................................................P.1.4 

 Concrete Shapes .................................................................P.1.4 

 Cast-in-Place Flexural Shapes .....................................P.1.5 

 Precast Flexural Shapes ...............................................P.1.6 

 Axially-Loaded Compression Members ......................P.1.8 

 Iron Shapes ........................................................................P.1.8 

 Cast Iron.......................................................................P.1.9 

 Wrought Iron................................................................P.1.9 

 Steel Shapes......................................................................P.1.10 

 Rolled Shapes.............................................................P.1.10 

 Built-up Shapes..........................................................P.1.13 

 Cables.........................................................................P.1.15 

 P.1.5 Connections.............................................................................P.1.16 

 Pin Connections................................................................P.1.17 

 Riveted Connections.........................................................P.1.18 

 Bolted Connections ..........................................................P.1.20 

 Welded Connections.........................................................P.1.21 

 Pin and Hanger Connections ............................................P.1.21 

 Splice Connections ...........................................................P.1.22 

 P.1.6 Decks.......................................................................................P.1.23 

 Deck Purpose....................................................................P.1.23 
Basic Concepts Primer 

TOPIC P.1: Bridge Components and Elements 

P.1-ii

 Deck Function ..................................................................P.1.24 

 Deck Materials .................................................................P.1.25 

 Timber Decks.............................................................P.1.25 

 Concrete Decks ..........................................................P.1.26 

 Steel Decks.................................................................P.1.27 

 Fiber Reinforced Polymer (FRP) Decks ....................P.1.28 

 Wearing Surfaces.......................................................P.1.28 

 Deck Joints, Drainage, Appurtenances, Signing, 

 and Lighting ....................................................................P.1.29 

 Deck Joints.................................................................P.1.29 

 Drainage Systems.......................................................P.1.32 

 Deck Appurtenances ..................................................P.1.32 

 Signing.......................................................................P.1.33 

 Lighting......................................................................P.1.34 

 P.1.7 Superstructure .........................................................................P.1.35 

 Superstructure Purpose.....................................................P.1.35 

 Superstructure Function....................................................P.1.35 

 Primary Elements .............................................................P.1.35 

 Secondary Elements .........................................................P.1.36 

 Superstructure Types........................................................P.1.37 

 Beams Bridges ..........................................................P.1.38 

 Arch Bridges ..............................................................P.1.43 

 Cable-Supported Bridges...........................................P.1.44 

 Movable Bridges........................................................P.1.45 

 Floating Bridges.........................................................P.1.47 

 Culverts......................................................................P.1.47 

 P.1.8 Bearings ..................................................................................P.1.48 

 Definition..........................................................................P.1.48 

 Primary Function..............................................................P.1.48 

 Basic Elements .................................................................P.1.48 

 Bearing Types...................................................................P.1.49 

 P.1.9 Substructure ............................................................................P.1.49 

 Substructure Purposes ......................................................P.1.49 

 Substructure Function.......................................................P.1.50 

 Abutments..................................................................P.1.51 

 Piers and Bents...........................................................P.1.52 
P.1.1 

Topic P.1 Bridge Components and Elements 

P.1.1 

Introduction The bridge inspector should be familiar with the terminology and elementary 

theory of bridge mechanics and materials. This topic presents the terminology 

needed by inspectors to properly identify and describe the individual elements that 

comprise a bridge. First the major components of a bridge are introduced. Then 

the basic member shapes and connections of the bridge are presented. Finally, the 

purpose and function of the major bridge components are described in detail. 

P.1.2 

NBIS Structure 

Length 

According to the Recording and Coding Guide for the Structure Inventory and 

Appraisal of the Nation’s Bridges the minimum length for a structure carrying 

traffic loads is 6.1meters (20 feet). The structure length is measured as shown on 

Figure P.1.1 

> 6.1 m (20')

> 6.1 m (20')

> 6.1 m (20')

> 6.1 m (20')

< 1⁄2 d(min)

d(min)

Figure P.1.1 NBIS Structure Length 

23 CFR Part 650.305 Definitions gives the definition of a bridge as it applies to the 

NBIS regulations. From the NBIS regulations, a bridge is defined as follows: a

structure including supports erected over a depression or an obstruction, such as 

water, highway, or railway, and having a track or passageway for carrying traffic 

or other moving loads, and having an opening measured along the center of the 

roadway of more than 20 feet between undercopings of abutments or spring lines 

of arches, or extreme ends of openings for multiple boxes; it may also include 

multiple pipes, where the clear distance between openings is less than half of the 

smaller contiguous opening 

P.1.3 

Major Bridge 

Components 

A thorough and complete bridge inspection is dependent upon the bridge 

inspector's ability to identify and understand the function of the major bridge 

components and their elements. Most bridges can be divided into three basic parts 

or components (see Figure P.1.1A): 

3⁄4 Deck 

3⁄4 Superstructure 

3⁄4 Substructure 
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.2

Deck

Superstructure

Abutment (part of

the substructure)

Pier (part of the

substructure)

 

Figure P.1.1A Major Bridge Components 

P.1.4 

Basic Member 

Shapes 

The ability to recognize and identify basic member shapes requires an 

understanding of the timber, concrete, and steel shapes used in the construction of 

bridges. 

Every bridge member is designed to carry a unique combination of tension, 

compression, and shear. These are considered the three basic kinds of member 

stresses. Bending loads cause a combination of tension and compression in a 

member. Shear stresses are caused by transverse forces exerted on a member. As 

such, certain shapes and materials have distinct characteristics in resisting the 

applied loads. For a review of bridge loadings and member responses, see 

Topic P.2. 

Timber Shapes Basic shapes, properties, gradings, deteriorations, protective systems, and 

examination of timber are covered in detail in Topic 2.1. 

Timber members are found in a variety of shapes (see Figure P.1.2). The sizes of 

timber members are generally given in nominal dimensions (such as in Figures 

P.1.2 and P.1.3). However, timber members are generally seasoned and surfaced 

from the rough sawn condition, making the actual dimension about 13 to 20 mm 

(1/2 to 3/4 inches) less than the nominal dimension. 

The physical properties of timber enable it to resist both tensile and compressive 

stresses. Therefore, it can function as an axially-loaded or bending member. 

Timber bridge members are made into three basic shapes: 

3⁄4 Planks 

3⁄4 Beams 

3⁄4 Piles 
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.3

 

Plank

(12" dia.)

300 mm (6" - 10")

150 mm – 250 mm

(10" - 14")

250 mm - 350 mm

Pile Beam

(12")

300 mm

(2")

50 mm

 

Figure P.1.2 Timber Shapes 

 Planks

Planks are characterized by elongated, rectangular dimensions determined by the 

intended bridge use. Plank thickness is dependent upon the distance between the 

supporting points and the magnitude of the vehicle load. A common dimension 

for timber planks is a 50 mm x 300 mm (2" x 12"), nominal or rough sawn. 

Dressed lumber dimensions would be 38 mm x 285 mm (1 1⁄2" x 11 1⁄4") (see 

Figure P.1.2). 

Planks are most often used for bridge decks on bridges carrying light or infrequent 

truck traffic. While some shapes and materials are relatively new, the use of 

timber plank decks has existed for centuries. Timber planks are advantageous in 

that they are economical, lightweight, readily available, and easy to erect. 

Beams

Timber beams have more equal rectangular dimensions than do planks, and they 

are sometimes square. Common dimensions include 250 mm by 250 mm (10 

inches by 10 inches) square timbers, and 150 mm by 350 mm (6 inches by 14 

inches) rectangular timbers. 

As the differences in the common dimensions of planks and timber beams 

indicate, beams are larger and heavier than planks and can support heavier loads, 

as well as span greater distances. As such, timber beams are used in bridge 

superstructures and substructures to carry bending and axial loads. 

 

Timbers can either be solid sawn or glued-laminated (see Figure P.1.3). Gluedlaminated timbers are advantageous in that they can be fabricated from smaller, 

more readily available pieces. Glued lamination also allows larger rectangular 

members to be formed without the presence of natural defects such as knots. 

Glued-laminated timbers are normally manufactured from well-seasoned 

laminations and display very little shrinkage after they are fabricated.
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.4

 

Figure P.1.3 Timber Beams 

 Piles 

Timber can also be used for piles. Piles are normally round, slender columns that 

support the substructure footing or partially form the substructure. Piles may be 

partially above ground or completely buried. 

Concrete Shapes Basic ingredients, properties, reinforcement, deterioration, protective systems, and 

examination of concrete are covered in detail in Topic 2.2. 

 

Figure P.1.4 Unusual Concrete Shapes 
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.5

Concrete is a unique material for bridge members because it can be formed into an 

infinite variety of shapes (see Figure P.1.4). Concrete members are used to carry 

axial and bending loads. Since bending results in a combination of compressive 

and tensile stresses, concrete bending members are typically reinforced with either 

reinforcing steel (producing reinforced concrete) or with prestressing steel 

(producing prestressed concrete) in order to carry the tensile stresses in the 

member. 

Cast-in-Place Flexural Shapes

The most common shapes of reinforced concrete members are (see Figure P.1.5): 

3⁄4 Slabs/Decks 

3⁄4 Rectangular beams 

3⁄4 Tee beams 

3⁄4 Channel beams 

Bridges utilizing these shapes and mild steel reinforcement have been constructed 

and were typically cast-in-place (CIP). Many of the designs are obsolete, but the 

structures remain in service. Concrete members of this type are used for short and 

medium span bridges. 

Slab/Deck

Channel

Tee

Rectangular

Figure P.1.5 Reinforced Concrete Shapes 

Concrete slabs are used for concrete decks and slab bridges. On concrete decks, 

the concrete spans the distance between superstructure members and is generally 

180 to 230 mm (7 to 9 inches) thick. On slab bridges, the slab spans the distance 

between piers or abutments, forming an integral deck and superstructure. Slab 

bridge elements are usually 300 to 600 mm (12 to 24 inches) thick. 

Rectangular beams are used for both superstructure and substructure bridge 

elements. Concrete pier caps are commonly rectangular beams which support the 

superstructure. 
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.6

Bridge use for tee beams is generally limited to superstructure elements. 

Distinguished by a "T" shape, tee beams combine the functions of a rectangular 

beam and slab to form an integral deck and superstructure. 

Bridge use for channel beams is limited to superstructure elements. This 

particular shape is precast rather than cast-in-place. Channel beams are formed in 

the shape of a "C" and placed legs down when erected. They function as both 

superstructure and deck and are typically used for shorter span bridges. 

Precast Flexural Shapes 

The most common shapes of prestressed concrete members are (see Figure P.1.6):

3⁄4 I-beams 

3⁄4 Bulb-tees 

3⁄4 Box beams 

3⁄4 Box girders 

3⁄4 Voided slabs 

These shapes are used for superstructure members. 

 I-Beam Bulb-tee

Voided Slab Box Beam

Box Girder

Figure P.1.6 Prestressed Concrete Shapes 

Prestressed concrete beams can be precast at a fabricator’s plant using high 
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.7

compressive strength concrete. Increased material strengths, more efficient 

shapes, the prestress forces and closely controlled fabrication allow these 

members to carry greater loads. Therefore, they are capable of spanning greater 

distances and supporting heavier live loads. Bridges using members of this type 

and material have been widely used in the United States since World War II. 

Prestressed concrete is generally more economical than conventionally reinforced 

concrete because the prestressing force lowers the neutral axis, putting more of 

the concrete section into compression. Also, the prestress steel is very high 

strength, so fewer pounds of steel are needed (see Figure P.1.7). 

 

Reinforced Prestressed

Figure P.1.7 Mild Steel Reinforced Concrete vs. Precast Prestressed Concrete 

I-beams, distinguished by their "I" shape, function as superstructure members and 

support the deck. This type of beam can be used for spans as long as 46 m (150 

feet). 

Bulb-tee beams are distinguished by their "T" shapes, with a bulb-shaped section 

(similar to the bottom flange of an I-beam) at the bottom of the vertical leg of the 

tee. This type of beam can be used for spans as long as 55 m (180 feet). 

Box beams, distinguished by a square or rectangular shape, usually have a beam 

depth greater than 430 mm (17 inches). Box beams can be adjacent or spread, 

and they are typically used for short and medium span bridges. 

Box girders, distinguished by their trapezoidal or rectangular box shapes, function 

as both deck and superstructure. Box girders are used for long span or curved 

bridges and can be precast and erected in segments or cast in place. 

Voided slabs, distinguished by their rectangular shape and their interior voids, are 

generally precast units supported by the substructure. The interior voids are used 

to reduce the dead load. Voided slabs can be used for spans of 9 to 24 m (30 to 

80 feet). 
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.8

Axially-Loaded Compression Members

Concrete axially-loaded compression members are used in bridges in the form of: 

3⁄4 Columns 

3⁄4 Arches 

3⁄4 Piles 

Because these members also carry varying bending forces, they contain steel 

reinforcement. 

Columns are straight members which can carry axial load, horizontal load, and 

bending and are used as substructure elements. Columns are commonly square, 

rectangular, or round. 

An arch can be thought of as a curved column and is commonly used as a 

superstructure element. Concrete superstructure arches are generally square or 

rectangular in cross section. 

Piles are slender columns that support the substructure footing or partially form 

the substructure. Piles may be partially above ground but are usually completely 

buried (see Figure P.1.8). 

Figure P.1.8 Concrete Pile Bent 

Iron Shapes Iron was used predominately as a bridge material between 1850 and 1900. 

Stronger and more fire resistant than wood, iron was widely used to carry the 

expanding railroad system during this period. 

There are two types of iron members: cast iron and wrought iron. Cast iron is 

formed by casting, whereas wrought iron is formed by forging or rolling the iron 

into the desired form. 
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.9

Cast Iron 

Historically, cast iron preceded wrought iron as a bridge material. The method of 

casting molten iron to form a desired shape was more direct than that of wrought 

iron. 

Casting allowed iron to be formed into almost any shape. However, because of 

cast iron's brittleness and low tensile strength, bridge members of cast iron were 

best used to carry axial compression loads. Therefore, cast iron members were 

usually cylindrical or box-shaped to efficiently resist axial loads. 

Wrought Iron

In the late 1800's, wrought iron virtually replaced the use of cast iron. The two 

primary reasons for this were that wrought iron was better suited to carry tensile 

loads and advances in rolling technology made wrought iron shapes easier to 

obtain and more economical to use. Advances in technology made it possible to 

form a variety of shapes by rolling, including: 

3⁄4 Rods and wire 

3⁄4 Bars 

3⁄4 Plates 

3⁄4 Angles 

3⁄4 Channels 

3⁄4 Beams 
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.10

Steel Shapes Steel bridge members began to be used in the United States in the late 1800’s and, 

by 1900, had virtually replaced iron as a bridge material. The replacement of iron 

by steel was the result of advances in steel making (see Figure P.1.9). These 

advances yielded a steel material that surpassed iron in both strength and 

elasticity. Steel could carry heavier loads and better withstand the shock and 

vibration of ever-increasing live loads. Since the early 1900’s, the quality of steel 

has continued to improve. Stronger and more ductile A36, A572, and A588 steels 

have replaced early grades of steel, such as A7.

 

Figure P.1.9 Steel Making Operation 

Due to their strength, steel bridge members are used to carry axial forces as well as 

bending forces. Steel shapes are generally either rolled or built-up. 

Rolled Shapes

Rolled steel shapes commonly used on bridges include (see Figure P.1.10): 

3⁄4 Bars and plates 

3⁄4 Angles 

3⁄4 Channels 

3⁄4 S Beams 

3⁄4 W Beams
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.11

Rods, Bars and Plates

Angles and Tees

I-beams and

Channels

 

Figure P.1.10 Common Rolled Steel Shapes 

The standard weights and dimensions of these shapes can be found in the 

American Institute of Steel Construction (AISC) Manual of Steel Construction. 

Bars and plates are formed into flat pieces of steel. Bars are normally considered 

to be up to 200 mm (8 inches) in width. Common examples of bars include lacing 

bars on a truss and steel eyebars. Plates are designated as flat plates if they are 

over 200 mm (8 inches) in width. A common example of a plate is the gusset plate 

on a truss. Bars and plates are dimensioned as follows: width x thickness x length. 

Examples of bar and plate dimensions include: 

3⁄4 Lacing bar: 50 mm x 10 mm x 0.4 m (2" x 3/8" x 1'-3") 

3⁄4 Gusset plate: 530 mm x 12 mm x 1.3 m (21" x 1/2" x 4'-4”) 

Angles are “L”-shaped members, the sides of which are called “legs”. Each angle 

has two legs, and the width of the legs can either be equal or unequal. When 

dimensioning angles, the two leg widths are given first, followed by the thickness 

and the length. Examples of angle dimensions include: 

3⁄4 L 102 mm x 102 mm x 6.4 mm x 965 mm (L 4" x 4" x 1⁄4" x 3'-2") 

3⁄4 2L’s 127 mm x 76 mm x 9.5 mm x 330 mm (2L’s 5" x 3" x 3/8" x 1'-1") 

Angles range in size from 25 mm x 25 mm x 6 mm to 200 mm x 200 mm x 28 mm 

(1"x1"x1/4" to 8"x8"x1-1/8"). Angles range in weight from less than 14.6 N/m (1 

pound per foot) to almost 880 N/m (60 pounds per foot). 

Angles, bars, and plates are commonly connected to form bracing members (see 

Figure P.1.11). 
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.12

Figure P.1.11 Bracing Members Made from Angles, Bars, and Plates 

Channels are squared-off "C"-shaped members and are used as diaphragms, struts, 

or other built-up members. The top and bottom parts of a channel are called the 

flanges. Channels are dimensioned by the depth (the distance between outside 

edges of the flanges) in mm or inches, the weight in kg per m or pounds per foot, 

and the length in mm or inches. Examples of channel dimensions include: 

3⁄4 C 230 x 22 x 2895 mm (C 9 x 15 x 9'-6") 

3⁄4 C 310 x 31 x 3416 mm (C 12 x 20.7 x 11'-2-1/2") 

When measuring a channel, it is not possible for the inspector to know how much 

the channel section weighs. In order to determine the weight, the inspector must 

record the flange width and the web depth. From this information, the inspector 

can then determine the true channel designation through the use of reference 

books. 

Standard channels range in depth from 75 mm to 380 mm (3 inches to 15 inches), 

and weights range from less than 73 N/m (5 pounds per foot) to 730 N/m (50 

pounds per foot). Nonstandard sections (called miscellaneous channels or MC) are 

rolled to depths of up to 600 mm (24 inches), weighing up to 845 N/m (60 pounds 

per foot). 

Beams are “I”-shaped sections used as main load-carrying members. The loadcarrying capacity generally increases as the member size increases. The early days 

of the iron and steel industry saw the various manufacturers rolling beams to their 

own standards. It was not until 1896 that beam weights and dimensions were 

standardized when the Association of American Steel Manufacturers adopted the 

American Standard beam. Because of this, I-beams are referred to by many 

designations, depending on their dimensions and the time period in which the 

particular shape was rolled. Today all I-beams are dimensioned according to their 

depth, weight, and length. 
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.13

Examples of beam dimensions include: 

3⁄4 S380x74 (S15x50) - an American Standard (hence the “S”) beam with a 

depth of 380 mm (15 inches) and a weight of 74 N/m (50 pounds per foot) 

3⁄4 W460x113 (W18x76) - a wide (W) flange beam with a depth of 460 mm 

(18 inches) and a weight of 113 N/m (76 pounds per foot) 

Some of the more common designations for rolled I-beams are: 

3⁄4 S = American Standard beam 

3⁄4 W = Wide flange beam 

3⁄4 WF = Wide flange beam 

3⁄4 CB = Carnegie beam 

3⁄4 M = Miscellaneous beam 

3⁄4 HP = H-pile 

When measuring an I-beam, the inspector needs to measure the depth, the flange 

width and thickness, and the web thickness (if possible). With this information, 

the inspector can then determine the beam designation from reference books. 

These beams normally range in depth from 75 to 900 mm (3 to 36 inches) and 

range in weight from 90 to over 4380 N/m (6 to over 300 pounds per foot). There 

are some steel mills that can roll beams up to 1120 mm (44 inches) deep. 

Built-up Shapes 

Built-up shapes offer a great deal of flexibility in designing member shapes. As 

such, they allow the bridge engineer to customize the members to their use. Builtup shapes are fabricated by either riveting or welding techniques. 

The practice of riveting steel shapes began in the 1800’s and continued through the 

1950’s. Typical riveted shapes include girders and boxes. 

Riveted girders are large I-beam members fabricated from plates and angles. 

These girders were fabricated when the largest rolled beams were still not large 

enough as required by design (see Figure P.1.12). 

Riveted boxes are large rectangular shapes fabricated from plates, angles, or 

channels. These boxes are used for cross-girders, truss chord members, and 

substructure members (see Figure P.1.13). 

As technology improved, the need for riveting was replaced by high strength bolts 

and welding. Popular since the early 1960's, welded steel shapes also include 

girders and boxes. 

Welded girders are large I-beam members fabricated from plates. They are 

referred to as welded plate girders and have replaced the riveted girder (see Figure 

P.1.14). 

Welded boxes are large, rectangular-shaped members fabricated from plates. 
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.14

Welded boxes are commonly used for superstructure girders, truss members, and 

cross girders. Welded box shapes have replaced riveted box shapes (see Figure 

P.1.15). 

top flange

cover plate

web plate

bottom flange

cover plate

flange

angle

Figure P.1.12 Riveted Plate Girder 

Channel (Typ.)

Angle (Typ.)

Plate (Typ.)

Lacing (Typ.)

Figure P.1.13 Riveted Box Shapes
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.15

top flange

web plate

bottom flange

 

Figure P.1.14 Welded I-Beam 

Figure P.1.15 Welded Box Shapes 

 Cables

Steel cables are tension members and are used in suspension, tied-arch, and cablestayed bridges. They are used as main cables and hangers of these bridge types 

(see Figure P.1.16). Refer to Topic 12.1 for a more detailed description of cablesupported bridges. 

 
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.16

Figure P.1.16 Cable-Supported Bridges 

P.1.5 

Connections Rolled and built-up steel shapes are used to make stringers, floor beams, girders, 

and truss members. These members require structural joints, or connections, to 

transfer loads between members. There are several different types of bridge 

member connections: 

3⁄4 Pin connections 

3⁄4 Riveted connections 

3⁄4 Bolted connections 

3⁄4 Welded connections 
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.17

SMALL PIN

MEDIUM PIN

LARGE PIN

BOLT

COTTER

3⁄4 Pin and hanger connections 

3⁄4 Splice connections 

Pin Connections Pins are cylindrical beams produced by forging, casting, or cold-rolling. The pin 

sizes and configurations are as follows (see Figure P.1.17): 

3⁄4 A small pin, 32 to 100 mm (1-1/4 to 4 inches) in diameter, is usually 

made with a cotter pin hole at one or both ends 

3⁄4 A medium pin, up to 250 mm (10 inches) in diameter, usually has 

threaded end projections for recessed retainer nuts 

3⁄4 A large pin, over 250 mm (10 inches) in diameter, is held in place by a 

recessed cap at each end and is secured by a bolt passing completely 

through the caps and pin 

Pins are often surrounded by a protective sleeve, which may also act as a spacer 

to separate members. Pin connections are commonly used in eyebar trusses, 

hinged arches, pin and hanger assemblies, and bearing supports (see Figure 

P.1.18). 

 

Figure P.1.17 Sizes of Bridge Pins 
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.18

Figure P.1.18 Pin-Connected Truss Members 

The major advantages of using pin connection details are the design simplicity 

and the ability for free end rotation. The design simplicity afforded by pin 

connections reduces the amount and complexity of design calculations. By 

allowing for free end rotation, pin connections reduce the level of stress in the 

member. 

The major disadvantages of pin connection details are the result of vibration, pin 

wear, unequal eyebar tension, unseen corrosion, and poor inspectability. 

Vibrations increase with pin connections because they allow more movement than 

more rigid types of connections. As a result of increased vibration, moving parts 

are subject to wear. 

Pin connections are used both in trusses and at expansion joints. Both truss and 

girder suspended spans or cantilever joints that permit expansion are susceptible 

to freezing or fixity of the pinned joints. This results in changes in the structure 

and undesirable stresses when axially-loaded members become bending members.

Some pins connect multiple eyebars. Since the eyebars may have different 

lengths, they may experience different levels of tension. In addition, because 

parts of the pin surface are hidden from view by the eyebars, links, or connected 

parts, an alternate method of completely inspecting the pin must be used (e.g., 

ultrasonic or pin removal). 

Riveted Connections The rivet was the primary fastener used in the early days of iron and steel bridges. 

The use of high strength bolts replaced rivets by the early 1960’s. 

The standard head is called a high-button or acorn-head rivet. Flat-head and 

countersunk-head rivets were also used in areas of limited clearance, such as an 

eyebar pin connection (see Figure P.1.19). 
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.19

High Button

Counter Sunk

Flat Head

Figure P.1.19 Types of Rivet Heads 

There are two grades of rivets typically found on bridges: 

3⁄4 ASTM A502 Grade 1 (formerly ASTM A141) low carbon steel 

3⁄4 ASTM A502 Grade 2 (formerly ASTM A195) high strength steel 

The rivet sizes most often used on bridges were 19, 23, or 25 mm (3/4, 7/8, or 1-

inch) shank diameters. Rivet holes were generally 2 mm (1/16-inch) larger than 

the rivet shank. While the hot rivet was being driven, the shank would increase 

slightly, filling the hole. As the rivet cooled, it would shrink in length, clamping 

together the connected elements. 

When the inspector can feel vibration on one head of the rivet while hitting the 

other rivet head with a hammer, this generally indicates that the rivet is loose. 

This method may not work with sheared rivets clamped between several plates. 
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.20

Bolted Connections Research into the use of high strength bolts began in 1947. The first 

specifications for the use of bolts were subsequently published in 1951. The 

economic and structural advantages of bolts over rivets led to their rapid use by 

bridge engineers. Bridges constructed in the late 1950’s may have a combination 

of riveted (shop) and bolted (field) connections (see Figure P.1.20). 

Structural bolts consist of three basic material designations: 

3⁄4 ASTM A307 low carbon steel 

3⁄4 ASTM A325M (ASTM A325 (AASHTO M 164)) high strength steel 

3⁄4 ASTM A490M (ASTM A490 (AASHTO M 253)) high strength alloy 

steel 

For further information on the bolts listed above or any other material properties 

visit the American Society for Testing and Materials International website at: 

www.astm.org . 

Figure P.1.20 Shop Rivets and Field Bolts 

The most commonly used bolts on bridges are 19, 23, and 25 mm (3/4, 7/8, and 1-

inch) in diameter. Larger bolts are often used to anchor the bearings. Bolt holes 

are typically 1/16-inch larger than the bolt. However, oversized and slotted holes 

are also permissible. 

The strength of high strength bolts is measured in tension. However, the 

inspection of high strength bolts on bridges involves many variables. Although 

the installation inspection of new high strength bolts often requires the use of a 

torque wrench, this method does not have any merit when inspecting high 

strength bolts on in-service bridges. The torque is dependent on factors such as 

bolt diameter, bolt length, connection design (bearing or friction), use of washers, 

paint and coatings, parallelism of connected parts, dirt, rust, and corrosion. 

The inspector must be cautioned that standard tables and formulas relating tension 

to torque are no longer considered valid. 
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.21

Simple techniques, such as looking and feeling for loose bolts, are the most 

common methods used by inspectors when inspecting bolts. 

Welded Connections Pins, rivets, and bolts are examples of mechanical fasteners forming non-rigid 

joints. A welded connection is not mechanical but rather is rigid one-piece 

construction. A properly welded joint, in which two pieces are fused together, is 

as strong as the joined materials. 

Similar to mechanical fasteners, welds are used to make structural connections 

between members and also to connect elements of a built-up member. Welds 

have also been used in the fabrication and erection of bridges as a way to 

temporarily hold pieces together prior to field riveting, bolting, or welding. Small 

temporary erection welds, known as tack welds, can cause serious fatigue 

problems to certain bridge members (see Figure P.1.21). Fatigue and fracture of 

steel bridge members are discussed in detail in Topic 8.1 (refer to 8.1.3 for factors 

affecting fatigue crack initiation). Welding is also used as a means of sealing 

joints and seams from moisture. 

Figure P.1.21 Close-up of Tack Weld on a Riveted Built-up Truss Member 

The first specification for using welds on bridges appeared in 1936. Welding 

eventually replaced rivets for fabricating built-up members. Welded plate girders, 

hollow box-like truss members, and shear connectors for composite decks are just 

a few of the advances attributed to welding technology. 

Welds need to be carefully inspected for cracks or signs of cracks (e.g., broken 

paint or rust stains) in both the welds and the adjoining base metal elements. 

Pin and Hanger 

Connections 

A pin and hanger connection is a type of hinge consisting of two pins and a 

hanger. Pin and hanger connections are used in an articulated (continuous bridge 

with hinges) or a suspended span configuration. The location of the connection 

varies depending on the type of bridge. In I-beam bridges, a hanger is located on 
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.22

either side of the webs (see Figure P.1.22). In suspended span truss bridges, each 

connection has a hanger which is similar in shape to the other truss members 

(with the exception of the pinned ends). 

Figure P.1.22 Pin and Hanger Connection 

Pin and hanger connections must be carefully inspected for signs of wear and 

corrosion. A potential problem can occur if corrosion of the pin and hanger 

causes the connection to "freeze," inhibiting free rotation. This condition does 

not allow the pin to rotate and results in additional stresses in the pin and hanger 

and adjacent girder. The failure of a pin and hanger connection can cause a 

partial or complete failure of the bridge. 

Splice Connections A splice connection is the joining of two sections of the same member, either in 

the fabrication shop or in the field. This type of connection can be made using 

rivets, bolts, or welds. Bolted splices are common in multi-beam superstructures 

due to the limited allowable shipping lengths (see Figure P.1.23). Welded flange 

splices are common in large welded plate girders as a means of fabricating the 

most economical section. 
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.23

Figure P.1.23 Bolted Field Splice 

P.1.6 

Decks The deck is that component of a bridge to which the live load is directly applied. 

Refer to Section 5 for a detailed explanation on the inspection and evaluation of 

decks. 

Deck Purpose The purpose of the deck is to provide a smooth and safe riding surface for the 

traffic utilizing the bridge (see Figure P.1.24). 

Figure P.1.24 Bridge Deck with a Smooth Riding Surface 
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Topic P.1: Bridge Components and Elements 

P.1.24

Deck Function The function of the deck is to transfer the live load and dead load of the deck to 

other bridge components. In most bridges, the deck distributes the live load to the 

superstructure (see Figure P.1.25). However, on some bridges (e.g., a concrete 

slab bridge), the deck and superstructure are one unit which distributes the live 

load directly to the bridge supports. 

Figure P.1.25 Underside View of a Bridge Deck 

Decks function in one of two ways: 

3⁄4 Composite decks - act together with their supporting members and 

increase superstructure capacity (see Figures P.1.26 and P.1.27)

3⁄4 Non-composite decks - are not integral with their supporting members 

and do not contribute to structural capacity of the superstructure

Wearing Surface

Figure P.1.26 Composite Deck and Steel Superstructure 
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.25

Figure P.1.27 Shear Studs on Top Flange of Girder (before Concrete Deck is 

Placed)

 

Deck Materials There are three common materials used in the construction of bridge decks: 

3⁄4 Timber 

3⁄4 Concrete 

3⁄4 Steel 

Timber Decks

Timber decks are normally referred to as decking or timber flooring, and the term 

is limited to the roadway portion which receives vehicular loads. Refer to Topic 

5.1 for a detailed explanation on the inspection and evaluation of timber decks. 

Five basic types of timber decks are: 

3⁄4 Plank deck (see Figure P.1.28) 

3⁄4 Nailed laminated deck 

3⁄4 Glued-laminated deck planks 

3⁄4 Stressed-laminated decks 

3⁄4 Structural composite lumber decks 
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.26

 

Figure P.1.28 Plank Deck 

 Concrete Decks 

Concrete permits casting in various shapes and sizes and has provided the bridge 

designer and the bridge builder with a variety of construction methods. Because 

concrete is weak in tension, it is used together with reinforcement to resist the 

tensile stresses (see Figure P.1.29). Refer to Topic 5.2 for a detailed explanation 

on the inspection and evaluation of concrete decks. 

There are several common types of concrete decks: 

3⁄4 Reinforced cast-in-place (CIP) - removable or stay-in-place forms 

3⁄4 Precast 

3⁄4 Precast, prestressed deck panels 

3⁄4 Precast prestressed deck panels with cast-in-place topping
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.27

 

Figure P.1.29 Concrete Deck 

 Steel Decks 

Steel decks are decks composed of either solid steel plate or steel grids (see Figure 

P.1.30). Refer to Topic 5.3 for a detailed explanation on the inspection and 

evaluation of steel decks. 

 

Figure P.1.30 Steel Grid Deck 
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.28

There are four common types of steel decks: 

3⁄4 Corrugated steel flooring 

3⁄4 Orthotropic deck 

3⁄4 Grid Deck - open, filled, or partially filled 

3⁄4 Buckle plate deck (still exist on some older bridges but are no longer 

used) 

Fiber Reinforced Polymer (FRP) Decks 

With the rise of technological development, innovative material such as carbonfiber-reinforced polymer (FRP) bridge decking has begun replacing existing 

highway bridge decks. Though FRP material is more expensive than conventional 

bridge materials such as concrete, it has several other advantages. These include 

lighter weight for efficient transport, better resistance to earthquakes, and easier 

installation. FRP bridge decking is also not affected by water or de-icing salts, 

which corrode steel and deteriorate concrete (see Figure P.1.31). 

 

Figure P.1.31 Fiber Reinforced Polymer (FRP) Deck 

 Wearing Surfaces 

Constant exposure to the elements makes weathering a significant cause of deck 

deterioration. In addition, vehicular traffic produces damaging effects on the deck 

surface. For these reasons, a wearing surface is often applied to the surface of the 

deck. The wearing surface is the topmost layer of material applied upon the deck 

to provide a smooth riding surface and to protect the deck from the effects of 

traffic and weathering. 
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.29

A timber deck may have one of the following wearing surfaces: 

3⁄4 Timber planks 

3⁄4 Asphalt/Bituminous 

Concrete decks may have wearing surfaces of: 

3⁄4 Concrete 

3⁄4 Latex modified concrete (LMC) 

3⁄4 Low slump dense concrete (LSDC) 

3⁄4 Asphalt or bituminous (see Figure P.1.32) 

3⁄4 Epoxy overlay with broadcast aggregate 

 

Figure P.1.32 Asphalt Wearing Surface on a Concrete Deck 

Deck Joints, Drainage, 

Appurtenances, Signing 

and Lighting 

Steel decks may have wearing or riding surfaces of: 

3⁄4 Serrated steel 

3⁄4 Concrete 

3⁄4 Asphalt 

Deck Joints 

The primary function of a deck joint is to accommodate the expansion, 

contraction, and rotation of the superstructure. The joint must also provide a 

smooth transition from an approach roadway to a bridge deck, or between 

adjoining segments of bridge deck. 
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.30

There are two major categories of deck joints: 

3⁄4 Open joints 

3⁄4 Closed joints 

Open Joints 

Open joints allow water and debris to pass through them. There are two types of 

unsealed joints: 

3⁄4 Formed joints 

3⁄4 Finger plate joints (see Figure P.1.33)

Figure P.1.33 Top View of a Finger Plate Joint

Closed Joints 

Closed joints are designed so water and debris do not pass through them. There 

are seven types of closed joints: 

3⁄4 Poured joint seal 

3⁄4 Compression seal (see Figure P.1.34) 
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.31

3⁄4 Cellular seal (closed cell foam) 

3⁄4 Sliding plate joint 

3⁄4 Prefabricated elastomeric seal – plank, sheet, or strip seal (see Figure 

P.1.35) 

3⁄4 Modular elastomeric seal

3⁄4 Asphaltic expansion joint

 

Figure P.1.34 Top View of an Armored Compression Seal in Place 

Figure P.1.35 Strip Seal

Extrusion

Strip

Seal
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.32

 Drainage Systems

The primary function of a drainage system is to remove water from the bridge 

deck, from under unsealed deck joints and from behind abutments and wingwalls. 

Deck Drainage System 

A deck drainage system has the following components: 

3⁄4 Deck drains 

3⁄4 Outlet pipes - to lead water away from drain 

3⁄4 Downspouts pipes - to transport runoff to storm sewers 

3⁄4 Cleanout plugs - for maintenance 

Joint Drainage System 

A joint drainage system is typically a separate gutter or trough used to collect 

water passing through a finger plate or sliding plate joint. 

Combining all these drainage components forms a complete deck drainage system.

Substructure Drainage Systems 

Substructure drainage allows the fill material behind an abutment or wingwall to 

drain any accumulated water. 

Substructure drainage is accomplished with weep holes or substructure drain pipes.

Deck Appurtenances

The proper and effective use of deck appurtenances minimizes hazards for traffic 

on the highways as well as waterways beneath the bridge. 

Bridge Barriers 

Bridge barriers can be broken down into two categories: 

3⁄4 Bridge railing - to guide, contain, and redirect errant vehicles 

3⁄4 Pedestrian railing - to protect pedestrians 

Examples of railing include: 

3⁄4 Timber plank rail 

3⁄4 Steel angles and bars 

3⁄4 Concrete pigeon hole parapet 

3⁄4 Combination bridge-pedestrian aluminum or steel railing 

3⁄4 New Jersey barrier - a very common concrete barrier (see Figure P.1.36)
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.33

 

Figure P.1.36 New Jersey Barrier 

Sidewalks and Curbs 

The function of sidewalks and curbs is to provide access to and maintain safety for 

pedestrians. Curbs serve to lessen the chance of vehicles crossing onto the 

sidewalk and endangering pedestrians. 

Signing

Signing serves to inform the motorist about bridge or roadway conditions that may 

be hazardous. 

Several signs likely to be encountered are: 

3⁄4 Weight limit (see Figure P.1.37) 

3⁄4 Speed traffic marker

3⁄4 Vertical clearance 

3⁄4 Lateral clearance 

3⁄4 Narrow underpass
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.34

Figure P.1.37 Weight Limit Sign 

 Lighting 

Types of lighting that may be encountered on a bridge include the following (see 

Figure P.1.38): 

3⁄4 Highway lighting 

3⁄4 Traffic control lights 

3⁄4 Aerial obstruction lights 

3⁄4 Navigation lights 

3⁄4 Signing lights 

Figure P.1.38 Bridge Lighting
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.35

Refer to Topic 5.4 for a more detailed explanation on joints, drainage, signing, and 

lighting of bridge decks. Refer to Topic 5.5 for a more detailed explanation on 

safety features and barriers of bridge decks. 

P.1.7 

Superstructure 

Superstructure Purpose The basic purpose of the superstructure is to carry loads from the deck across the 

span and to the bridge supports. The superstructure is that component of the bridge 

which supports the deck or riding surface of the bridge, as well as the loads 

applied to the deck. 

Superstructure Function The function of the superstructure is to transmit loads. Bridges are named for their 

type of superstructure. Superstructures may be characterized with regard to their 

function (i.e., how they transmit loads to the substructure). Loads may be 

transmitted through tension, compression, bending, or a combination of these 

three. 

There are three common materials used in the construction of bridge 

superstructures: 

3⁄4 Timber 

3⁄4 Concrete 

3⁄4 Steel 

Primary Elements Most superstructures are made up of two basic elements: 

3⁄4 Floor system - Receives traffic loads from the deck and distributes them to 

the main supporting elements (see Figure P.1.39) 

 

Figure P.1.39 Floor System 
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.36

3⁄4 Main supporting elements - Transfer all loads to the substructure units (see 

Figure P.1.40) 

Figure P.1.40 Main Supporting Elements of Deck Arch 

Secondary Elements Secondary elements are elements which do not normally carry traffic loads 

directly. Typical secondary elements are: 

3⁄4 Diaphragms (see Figure P.1.41) 

3⁄4 Cross or X-bracing (see Figure P.1.42) 

3⁄4 Lateral bracing (see Figure P.1.43) 

3⁄4 Sway-portal bracing (see Figure P.1.43)

Figure P.1.41 Diaphragms 
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.37

Figure P.1.42 Cross or X-Bracing

Figure P.1.43 Top Lateral Bracing and Sway Bracing

Superstructure Types There are three basic types of bridges (see Figure P.1.44): 

3⁄4 Beam 

3⁄4 Arch 

3⁄4 Cable-supported
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.38

Beam

Cable Supported

Arch

Figure P.1.44 Three Basic Bridge Types

 Beam Bridges 

In the case of beam bridges, loads from the superstructure are transmitted 

vertically to the substructure. Examples of beam bridges include: 

3⁄4 Slabs (concrete) (see Figure P.1.45) 

3⁄4 Beams (timber, concrete, or steel) (see Figures P.1.46, P.1.50, P.1.51) 

3⁄4 Girders (concrete or steel) (see Figures P.1.47, P.1.48, P.1.49, P.1.52) 

3⁄4 Trusses (timber or steel) (see Figures P.1.53 and P.1.54)

Figure P.1.45 Slab Bridge 
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Topic P.1: Bridge Components and Elements 

P.1.39

Figure P.1.46 Timber Beam Bridge

Figure P.1.47 Prestressed Concrete Multi-Girder Bridge
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.40

Figure P.1.48 Girder Floorbeam Stringer Bridge

Figure P.1.49 Curved Girder Bridge
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Topic P.1: Bridge Components and Elements 

P.1.41

Figure P.1.50 Tee Beam Bridge

Figure P.1.51 Adjacent Box Beam Bridge
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.42

Figure P.1.52 Steel Box Girder Bridge

Figure P.1.53 Deck Truss Bridge
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.43

Figure P.1.54 Through Truss Bridge

 Arch Bridges 

In the case of arch bridges, the loads from the superstructure are transmitted 

diagonally to the substructure. True arches are in pure compression. Arch bridges 

can be constructed from timber, concrete, or steel (see Figures P.1.55 and P.1.56).

Figure P.1.55 Concrete Deck Arch Bridge 
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.44

Figure P.1.56 Through Arch Bridge

 Cable-Supported Bridges 

In the case of cable-supported bridges, the superstructure loads are resisted by 

cables which act in tension. The cable forces are then resisted by the substructure 

anchorages and towers. Cable-supported bridges can be either suspension or 

cable-stayed (see Figures P.1.57 and P.1.58). Refer to Topic 12.1 for a more 

detailed explanation on cable-supported bridges. 

Figure P.1.57 Steel Suspension Bridge 
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.45

Figure P.1.58 Cable-stayed Bridge

 

Movable Bridge 

Movable bridges are constructed across designated "Navigable Waters of the 

United States," in accordance with "Permit Drawings" approved by the U.S. Coast 

Guard. The purpose of a movable bridge is to provide the appropriate channel 

width and underclearance for passing water vessels when fully opened. Refer to 

Topic 12.2 for a more detailed explanation on movable bridges. 

Movable bridges can be classified into three general groups: 

3⁄4 Bascule (see Figure P.1.59) 

3⁄4 Swing (see Figure P.1.60) 

3⁄4 Lift (see Figure P.1.61)
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.46

Figure P.1.59 Bascule Bridge 

Figure P.1.60 Swing Bridge
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.47

Figure P.1.61 Lift Bridge

 

Floating Bridges

Although uncommon, some states have bridges that are not supported by a 

substructure. Instead, they are supported by water. The elevation of the bridge will 

change as the water level fluctuates. 

Figure P.1.62 Floating Bridge

 

Culverts

A culvert is primarily a hydraulic structure, and its main purpose is to transport 

water flow efficiently. 
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.48

Culverts are often viewed as small bridges, being constructed entirely below and 

independent of the roadway surface. However, culverts do not have a deck, 

superstructure, or substructure (see Figure P.1.63). Refer to Topics P.3, 12.3 and 

12.4 for a more detailed explanation on culverts. 

Figure P.1.63 Culvert

P.1.8 

Bearings 

Definition A bridge bearing is a superstructure element which provides an interface between 

the superstructure and the substructure. 

Primary Function There are three primary functions of a bridge bearing: 

3⁄4 Transmit all loads from the superstructure to the substructure 

3⁄4 Permit longitudinal movement of the superstructure due to thermal 

expansion and contraction 

3⁄4 Allow rotation caused by dead and live load deflection 

Bearings that do not allow for translation or movement of the superstructure are 

referred to as fixed bearings. Bearings that allow for the displacement of the 

structure are known as expansion bearings. Both fixed and expansion bearings 

permit rotation. 

Basic Elements A bridge bearing can be broken down into four basic elements (see Figure P.1.64): 

3⁄4 Sole plate 

3⁄4 Masonry plate 
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.49

3⁄4 Bearing or bearing surfaces 

3⁄4 Anchorage 

Figure P.1.64 Typical Bearing Showing Four Basic Elements 

Bearing Types Various bearing types have evolved out of the need to accommodate superstructure 

movement and rotation: 

3⁄4 Sliding plate bearings 

3⁄4 Roller bearings 

3⁄4 Rocker bearings 

3⁄4 Pin and link bearings 

3⁄4 Elastomeric bearings 

3⁄4 Pot bearings 

3⁄4 Restraining bearings 

3⁄4 Isolation bearings 

Refer to Topic 9.1 for a more detailed explanation on bridge bearings. 

P.1.9 

Substructure The substructure is the component of a bridge which includes all the elements 

which support the superstructure. 

Substructure Purposes The purpose of the substructure is to transfer the loads from the superstructure to 

the foundation soil or rock. Typically the substructure includes all elements below 

the bearings. The loads are then distributed to the earth through the footing. 

Sole Plate 

Anchorage 

Masonry 

Plate 

Bearing 

Device 
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.50

Substructure Function Substructure units function as both axially-loaded and bending members. These 

units resist both vertical and horizontal loads applied from the superstructure and 

roadway embankment. Substructures are divided into two basic categories: 

3⁄4 Abutments 

3⁄4 Piers and bents 

Abutments provide support for the ends of the superstructure and retain the 

roadway approach embankment (see Figure P.1.65). Piers and bents provide 

support for the superstructure at intermediate points along the bridge spans with a 

minimum obstruction to the flow of traffic or water (see Figure P.1.66). 

Figure P.1.65 Concrete Abutment 
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.51

footing

abutment stem

backwall

wing

bridge seat

footing

abut.

stem

backwall

Figure P.1.66 Concrete Pier 

 Abutments 

Basic types of abutments include: 

3⁄4 Cantilever or full height abutment - extends from the grade line of the 

roadway or waterway below, to that of the road overhead (see Figure 

P.1.67). 

3⁄4 Stub, semi-stub, or shelf abutment - located within the topmost portion of 

the end of an embankment or slope. In the case of a stub, less of the 

abutment stem is visible than in the case of the full height abutment. 

Most new construction uses this type of abutment. These abutments may 

be required to be supported on deep foundations (see Figure P.1.68). 

3⁄4 Spill-through or open abutment - consists of columns and has no solid 

wall, but rather is open to the embankment material. The approach 

embankment material is usually rock (see Figure P.1.69).

Figure P.1.67 Cantilever Abutment (or Full Height Abutment)
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.52

footing

abutment stem

backwall

wing

bridge seat

footing

abut.

stem

backwall

footing

cap beam

backwall

floating

wingwall

bridge seat

footing

cap

beam

backwall

column column

Figure P.1.68 Stub Abutment 

Figure P.1.69 Open Abutment

Refer to Topic 10.1 for a more detailed explanation on bridge abutments. 

Piers and Bents 

A pier has only one footing at each substructure unit (the footing may serve as a 

pile cap). A bent has several footings or no footing, as is the case with a pile bent. 

Refer to Topic 10.2 for a more detailed explanation on bridge piers and bents. 

There are four basic types of piers: 

3⁄4 Solid shaft pier (see Figures P.1.70 and P.1.71) 

3⁄4 Column pier (see Figure P.1.72) 

3⁄4 Column pier with web wall (see Figure P.1.73) 

3⁄4 Cantilever or hammerhead pier (see Figure P.1.74)
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Topic P.1: Bridge Components and Elements 

P.1.53

Figure P.1.70 Solid Shaft Pier 

Figure P.1.71 Solid Shaft Pier
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Topic P.1: Bridge Components and Elements 

P.1.54

Figure P.1.72 Column Pier

Figure P.1.73 Column Pier with Web Wall 
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Topic P.1: Bridge Components and Elements 

P.1.55

Figure P.1.74 Cantilever or Hammerhead Pier

There are two basic types of bents: 

3⁄4 Column bent (see Figure P.1.75) 

3⁄4 Pile bent (see Figure P.1.76)

Figure P.1.75 Column Bent 
SECTION P: Basics Concepts Primer 

Topic P.1: Bridge Components and Elements 

P.1.56

Figure P.1.76 Pile Bent