9.1-i

Table of Contents

Section 9 ..................................................................................................................................................

Inspection and 

Evaluation of Bridge 

Bearings 

 9.1 Bridge Bearings...................................................................................... 9.1.1 

 

 9.1.1 Introduction.............................................................................. 9.1.1 

 Fixed and Expansion Bearings ........................................... 9.1.2 

 

 9.1.2 Four Basic Elements of a Bearing............................................. 9.1.2 

 Sole Plate............................................................................ 9.1.2 

 Bearing or Bearing Surface ................................................ 9.1.2 

 Masonry Plate..................................................................... 9.1.2 

 Anchorage .......................................................................... 9.1.2 

 9.1.3 Bearing Types and Functionality .............................................. 9.1.3 

 Sliding Plate Bearings ........................................................ 9.1.3 

 Lubricated Steel Plates................................................. 9.1.3 

 Lead Sheets Between Steel Plates................................ 9.1.4 

 Bronze Bearing Plates.................................................. 9.1.5 

 Asbestos Sheet Packing Between Metal Plates............ 9.1.5 

 Self-Lubricating Bronze Bearings ............................... 9.1.5 

 Roofing Felt / Tar Paper .............................................. 9.1.6 

 PTFE on Stainless Steel Plates .................................... 9.1.6 

 Roller Bearings................................................................... 9.1.6 

 Single Roller Bearings ................................................. 9.1.6 

 Roller Nest Bearings.................................................... 9.1.7 

 Rocker Bearings ................................................................. 9.1.8 

 Segmental Rocker Bearings......................................... 9.1.9 

 Rocker Nest Bearings ................................................ 9.1.10 

 Pinned Rocker Bearings............................................. 9.1.11 

 Elastomeric Bearings........................................................ 9.1.12 

 Plain Neoprene Pads .................................................. 9.1.12 

 Laminated Neoprene Pads ......................................... 9.1.13 

 Seismic Bearings .............................................................. 9.1.14 

 Isolation Bearings ...................................................... 9.1.14 
SECTION 9: Inspection and Evaluation of Bridge Bearings 

TOPIC 9.1: Bridge Bearings 

9.1-ii

 Friction-Pendulum Bearings ...................................... 9.1.15 

 High-dampening Rubber Bearings............................. 9.1.15 

 Pot Bearings ..................................................................... 9.1.16 

 Neoprene Pot Bearings .............................................. 9.1.16 

 Spherical Pot Bearings............................................... 9.1.16 

 Restraining Bearings ........................................................ 9.1.17 

 Pin and Link Bearings................................................ 9.1.18 

 9.1.4 Inspection Procedures ............................................................. 9.1.19 

 Inspection of Steel Bearings............................................. 9.1.20 

 Visual Procedures ...................................................... 9.1.20 

 Physical Procedures ................................................... 9.1.20 

 Advanced Procedures................................................. 9.1.20 

 General Procedures .................................................... 9.1.22 

 Sliding Plate Bearings................................................ 9.1.25 

 Roller Bearings .......................................................... 9.1.27 

 Rocker Bearings......................................................... 9.1.28 

 Pin and Link Bearings................................................ 9.1.29 

 Pot Bearings............................................................... 9.1.30 

 Restraining Bearings.................................................. 9.1.31 

 Inspection of Elastomeric Bearings.................................. 9.1.31 

 Neoprene Bearings..................................................... 9.1.31 

 Isolation Bearings ...................................................... 9.1.33 

 9.1.5 Evaluation ............................................................................... 9.1.34 

 NBI Rating Guidelines ..................................................... 9.1.34 

 Element Level Condition State Assessment..................... 9.1.34 

 Serious Bearing Conditions.............................................. 9.1.35 
9.1.1 

Section 9 

Inspection and Evaluation of Bridge 

Bearings 

Topic 9.1 Bridge Bearings 

9.1.1 

Introduction A bridge bearing is a superstructure element that provides an interface between the 

superstructure and the substructure. The three primary functions of a bridge 

bearing are: 

3⁄4 To transmit loads from the superstructure to the substructure 

3⁄4 To allow rotation caused by dead load and live load deflection. 

3⁄4 To permit horizontal movement of the superstructure due to thermal 

expansion and contraction (expansion bearings only) 

1. Transmit Superstructure Loads

3. Horizontal Movement

2. Rotation

Bearing

V

H

Figure 9.1.1 Three Functions of a Bearing 
SECTION 9: Inspection and Evaluation of Bridge Bearings 

TOPIC 9.1: Bridge Bearings 

9.1.2 

Fixed and Expansion 

Bearings 

Bearings that do not allow for horizontal translation or movement of the 

superstructure are referred to as fixed bearings. Bearings that do allow for 

horizontal translation or movement of the superstructure are known as expansion 

bearings. Both fixed and expansion bearings permit rotation that occurs as loads 

are applied or removed from the bridge. 

Figure 9.1.2 Fixed and Expansion Bearings 

9.1.2 

Four Basic 

Elements of a 

Bearing 

A bridge bearing consists of four basic elements; sole plate, bearing or bearing 

surface, masonry plate and anchorage. 

Sole Plate The sole plate is a steel plate that is attached to the bottom of girders or beams or 

truss chords. A sole plate may also be embedded into the bottom flange of a 

prestressed concrete girder. With concrete beams, girders, or slabs, the lower 

flange or bottom of the section may function as a sole plate. 

Bearing or Bearing 

Surface 

The bearing or bearing surface is secured to the sole plate and masonry plate and 

provides the function of transmitting the forces from the sole plate to the masonry 

plate. 

Masonry Plate The masonry plate is a steel plate that is attached to the bearing seat of an 

abutment or pier. The masonry plate serves to distribute vertical forces from the 

bearing to the substructure unit. 

Anchorage The anchor bolts connect the bearing to the substructure unit. Anchor bolts are 

designed to restrain the masonry plate from horizontal translation. The anchor 

bolts can, however, pass through or alongside the expansion bearing element to 

provide restraint against transverse movement. The local or governing agency 

requirements should be checked to determine the minimum bolt diameter and the 
SECTION 9: Inspection and Evaluation of Bridge Bearings 

TOPIC 9.1: Bridge Bearings 

9.1.3 

minimum embedded length. 

Figure 9.1.3 Elements of a Typical Bridge Bearing 

Not all bearings have all four of these distinct elements. All bearings do, however, 

have at least the bearing or bearing surface. 

9.1.3 

Bearing Types and 

Functionality 

Various expansion bearing types have evolved out of the need to accommodate 

superstructure movement. These expansion bearings include: 

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 Seismic Bearings 

3⁄4 Pot bearings 

3⁄4 Restraining bearings 

Sliding Plate Bearings Several types of sliding plate bearings have been used in bridges over the years. 

They are primarily used on structures with a span length of less than 12 m (40 

feet). Longitudinal movement is provided by one plate sliding upon another. The 

basic difference in the various types is the method of lubrication. Among the 

various types of plates are those presented below. 

Lubricated Steel Plates

The first generation of lubricated steel plates consisted of two steel plates with the 

bearing surfaces planed smooth. Lubrication between the plates consisted of 

grease, graphite, and tallow. Unfortunately, the lubricant tended to hold dirt which 

Sole Plate 

Masonry Plate 

Bearing Device 

Anchorage 
SECTION 9: Inspection and Evaluation of Bridge Bearings 

TOPIC 9.1: Bridge Bearings 

9.1.4 

absorbed moisture, eventually corroding and freezing the bearing. “Freezing”, as 

used in describing bearings, indicates that the bearing movement or rotation is 

restricted due to corrosion, mechanical binding, dirt buildup, or other interference. 

The bearing can not move or rotate as intended. 

The next generation of sliding steel plates consisted of a small plate sliding on a 

considerably larger one. The theory behind this was that if the contact area were 

smaller, the forces transmitted would overcome the freezing forces. However, the 

smaller plate actually wore a groove in the larger one, eventually freezing the 

bearing anyway. 

Figure 9.1.4 Lubricated Steel Plate Bearing

 Lead Sheets Between Steel Plates

By placing a thin lead sheet between the steel plates, it is possible to keep the 

plates from freezing together when they corrode. Lead sheets are used to reduce 

corrosion between the plates, thereby providing more freedom of movement. 

However, in this type of bearing, the lead has a tendency to work its way out from 

between the plates. 
SECTION 9: Inspection and Evaluation of Bridge Bearings 

TOPIC 9.1: Bridge Bearings 

9.1.5 

 Bronze Bearing Plates

A bronze bearing plate was introduced to avoid the corrosion problems of steel 

plates in contact with one another. Since bronze does not corrode, it was used to 

maintain the freedom of movement. Although corrosion is reduced, the bronze, 

which is soft material, becomes worn due to trapped dirt and the action of 

expansion and contraction. Eventually, a freezing of the plates may take place. 

Figure 9.1.5 Bronze Sliding Plate Bearing

 Asbestos Sheet Packing Between Metal Plates

A graphite-impregnated asbestos sheet has been used between steel bearing plates 

to provide some movement in spans of less than 12 m (40 feet). 

Self-Lubricating Bronze Bearings

The self-lubricating bronze bearing was developed to ensure a graphite lubricant 

between bearing plates, regardless of their wear. Portions of the face of the 

bearing were removed and replaced with a graphite compound, which 

continuously lubricated the bearing surfaces. Some manufacturers claim that these 

bearings are corrosion resistant and never require any maintenance. The bearings 

may be maintenance free if they are kept free from dirt and abrasive dusts. 

These bearings are widely available in many different forms, including plates, 

plates with one side cut to a radius, and half cylinders. The (top) flat side provides 

translation movement, and rotational movement is provided by the (bottom) radius 

side. (See Figure 9.1.6). 
SECTION 9: Inspection and Evaluation of Bridge Bearings 

TOPIC 9.1: Bridge Bearings 

9.1.6 

Figure 9.1.6 Self-lubricating Bronze Sliding Plate Bearing

 Roofing Felt / Tar Paper 

Another type of bearing consists of oil-soaked felt or tar paper that has been dusted 

with graphite. Several layers are placed on the bridge seat with the superstructure 

placed directly on it. This is a simple but effective bearing that is commonly used 

on short span concrete slabs and girders that sit on concrete abutments. These 

bearing types provide limited horizontal movement. 

PTFE on Stainless Steel Plates

A compound known as “polytetrafluoroethylene” (PTFE or TFE) has the lowest 

coefficient of friction of any of the commonly available materials, making it quite 

desirable for use in bridge bearings. 

Various types of bearings have been offered to take advantage of PTFE's 

characteristics. Today, bearings using PTFE have a sheet of stainless steel 

underneath the sole plate to slide across the PTFE. Pure PTFE has a low 

compressive strength and a high coefficient of thermal expansion. To make it 

suitable for use in bridge bearings, PTFE must be combined with suitable fillers. 

These fillers are typically glass fiber and bronze and, while giving strength to the 

PTFE, they do not increase its low coefficient of friction. 

Roller Bearings A roller bearing consists of a cylinder, which “rolls” between the sole plate and 

masonry plate as the superstructure expands, and contracts. Roller bearings are 

used in a wide variety of forms, including single rollers and roller nests. 

Single Roller Bearings

The single roller is one of the most widely used expansion bearings. Rollers can 

vary in size, with specified diameters ranging from 150 to 380 mm (6 to 15 

inches). While the larger rollers are less susceptible to corrosion problems, dirt 

may get trapped in the contact areas along the top and bottom of the bearing. This 
SECTION 9: Inspection and Evaluation of Bridge Bearings 

TOPIC 9.1: Bridge Bearings 

9.1.7 

enables moisture absorption, eventually deteriorating the bearing surface. 

However, because only a small portion of the roller actually becomes corroded, the 

corroded roller can be rotated and another portion of the roller surface can be used. 

Many single roller bearings are made of corrosion resistant steel. 

An unrestrained roller may gradually work itself out from underneath the bridge

superstructure. For this reason, pintle pins are used to keep the roller in place. 

These pins fit tightly into the roller but loosely into the upper and lower plates. 

The loose fit allows for the necessary structure movement. 

Figure 9.1.7 Single Roller Bearing 

 Roller Nest Bearings

First used in steel bridges in the early 1900's, roller nests consist of a group of 

rollers, each about 38 to 50 mm (11⁄2 to 2 inches) in diameter. When clean, roller 

nests work well. However, the small rollers offer many places for dirt and 

moisture to collect. This results in wear and corrosion of the rollers, and 

ultimately results in bearing failure. Attempts to seal this bearing require careful 

maintenance of protective covers and skirts and are typically unsucessful. (See 

Figure 9.1.8). 
SECTION 9: Inspection and Evaluation of Bridge Bearings 

TOPIC 9.1: Bridge Bearings 

9.1.8 

Figure 9.1.8 Roller Nest Bearing

Rocker Bearings The rocker bearing functions in a similar manner to the roller bearing and is 

generally used where a substantial amount of longitudinal movement is required

(see Figure 9.1.9). As with roller bearings, rocker bearings come in different 

forms, such as segmental rockers, rocker nests, and pinned rockers. 

Figure 9.1.9 Rocker Bearing 
SECTION 9: Inspection and Evaluation of Bridge Bearings 

TOPIC 9.1: Bridge Bearings 

9.1.9 

 Segmental Rocker Bearings

These rockers evolved out of the use of large rollers. When the rollers get up to 

510 mm (20 inches) in diameter, they become very heavy and difficult to handle. 

Since only a small portion of the roller bearing is actually in contact between the 

sole plate and masonry plate, the unused portion can be cut away and a substantial 

weight savings can be realized. 

Larger segmental rockers have also been fabricated from rectangular blocks, 

rounded at both ends, which allow the bearing to roll and the horizontal movement 

to take place. 

Figure 9.1.10 Segmental Rocker Bearing
SECTION 9: Inspection and Evaluation of Bridge Bearings 

TOPIC 9.1: Bridge Bearings 

9.1.10

 Rocker Nest Bearings

A group of several rockers forms a rocker nest. Rocker nests provide many small 

areas for dirt and moisture to collect, similar to roller nest bearings. Moisture can 

lead to corrosion which can result in a bearing failure. 

Figure 9.1.11 Segmental Rocker Nest Bearing
SECTION 9: Inspection and Evaluation of Bridge Bearings 

TOPIC 9.1: Bridge Bearings 

9.1.11

 Pinned Rocker Bearings 

The pinned rocker is the most popular rocker bearing in use today. The top is 

basically a large pin and tends to keep the bearing aligned correctly. Longitudinal 

movement is provided by the rotation afforded by the pin and the rolling provided 

by the rocker. When exposed to adverse environmental conditions, however, the 

pin can corrode and freeze. Pinned rocker bearings can be quite large and are 

commonly used for relatively long spans and heavy loads. Holes in the radius 

portion of the bearing may be slotted to accommodate longitudinal movement. 

Figure 9.1.12 Pinned Rocker Bearing
SECTION 9: Inspection and Evaluation of Bridge Bearings 

TOPIC 9.1: Bridge Bearings 

9.1.12

Elastomeric Bearings Elastomeric bearings include both plain and laminated neoprene pads. Neoprene 

is a heavy rubber like material that deforms slightly under compression or shear. 

Plain Neoprene Pads

A plain neoprene bearing consists of a rectangular pad of pure neoprene and is 

used primarily on short span, prestressed concrete structures. Neoprene bearings 

are popular for steel beam bridges as well. Expansion and contraction are 

achieved through a shearing deformation of the neoprene. 

Typically these bearings are of uniform thickness and are rectangular with parallel 

sides, but round, disc-shaped pads have also been used. 

Various means are used to prevent the neoprene bearing from “walking” out of 

position from under a beam. An epoxy compound has been used to bond the pad 

to the beam and the bridge seat, but it has not always been successful. 

Figure 9.1.13 Plain Neoprene Bearing Pad 
SECTION 9: Inspection and Evaluation of Bridge Bearings 

TOPIC 9.1: Bridge Bearings 

9.1.13

 Laminated Neoprene Pads 

A laminated neoprene bearing is simply a stack of neoprene pads with steel or 

fiberglass plates separating them. The plates are not visible if the entire bearing is 

encased in neoprene. Laminated bearing pads are used on longer structures where 

the expansion and contraction requirements and the vertical superstructure loads 

are greater. 

Although a single, thicker pad could conceivably do the job of the laminated 

bearing, excess bulging and wearing of the pad would dramatically decrease its 

useful life. The laminated bearing eliminates this excess bulging and allows the 

expansion and contraction without excessive wear. 

Figure 9.1.14 Laminated Neoprene Bearing Pad
SECTION 9: Inspection and Evaluation of Bridge Bearings 

TOPIC 9.1: Bridge Bearings 

9.1.14

Seismic Bearings Isolation Bearings 

The isolation bearing was developed to protect structures against earthquake 

damage. It is similar to the laminated neoprene bearing in that it is a sandwich of 

neoprene and steel plates. It also contains a lead core that is used primarily for 

horizontal seismic loads. A cover of neoprene protects the steel plates but the top 

of the lead core remains exposed. 

The isolation bearing behaves like a laminated bearing when exposed to normal 

bridge loading. The lead core stiffens the bearing and helps it to resist these loads. 

However, under seismic loads, the lead core is designed to yield, thereby making 

the bearing more flexible and allowing it to isolate the bridge from the effects of 

earthquake motion. 

Figure 9.1.15 Lead Core Isolation Bearing

Figure 9.1.16 Lead Core Isolation Bearing 
SECTION 9: Inspection and Evaluation of Bridge Bearings 

TOPIC 9.1: Bridge Bearings 

9.1.15

 Friction Pendulum Bearings 

Another bearing type designed to protect against earthquake damage is friction 

pendulum bearings. The bearings are designed to reduce lateral loads and shaking 

movements transmitted to the structure. They can protect structures and their 

contents during strong, high magnitude earthquakes and can accommodate near 

fault pulses and deep soil sites. 

Friction pendulum bearings incorporate the characteristics of a pendulum to 

lengthen the natural period of the isolated structure so as to avoid the strongest 

earthquake forces. The period of the bearing is selected by choosing the radius of 

curvature of the concave surface. It is independent of the loads of the 

superstructure. Torsion motions of the substructure are minimized because the 

center of stiffness of the bearings automatically coincides with the center of mass 

of the superstructure. 

Figure 9.1.17 Friction Pendulum Bearing

 High Dampening Rubber Bearings 

High dampening rubber bearings were also developed to protect structures from 

the damage of earthquakes. Under service load conditions, the bearing provides 

support in a similar fashion to elastomeric bearings. Its rigidity is provided by a 

high rubber modulus at small shear strains. During an earthquake, a special 

hysteretic rubber compound in the bearing dissipates the energy of the earthquake. 

As a result, the structure is isolated from the shaking forces of the earthquake and 

is less likely to collapse. 
SECTION 9: Inspection and Evaluation of Bridge Bearings 

TOPIC 9.1: Bridge Bearings 

9.1.16

Pot Bearings Pot bearings allow for the multi-dimensional rotations of a structure. There are 

two different pot bearing configurations: neoprene and spherical. 

Neoprene Pot Bearings 

A neoprene pot bearing has a stainless steel plate that is attached to the sole plate. 

This stainless steel plate slides on a polytetrafluoroethylene (PTFE) disc. The 

PTFE disc is attached to a steel piston, which rests on a neoprene pad, allowing for 

the rotation of the structure. The pad rests in a shallow steel cylinder that is 

attached to the masonry plate. This cylinder is referred to as the pot. Guide bars 

in the expansion pot bearing restrict transverse movement. 

A fixed bearing version of this configuration does not possess the stainless steel 

plate or the PTFE disc. 

Figure 9.1.18 Pot Bearing 

 Spherical Pot Bearings

A spherical pot bearing has a stainless steel plate that is attached to the sole plate. 

This stainless steel plate slides on a disc of PTFE that is bonded to an aluminum 

alloy casting. The casting has a flat top and a spherical bottom. The bottom of the 

casting fits into another PTFE-coated aluminum alloy casting. The spherical 

shaped castings allow for the rotation of the structure. 

A fixed bearing version of this configuration has the upper aluminum casting 

attached to the sole plate. There is no stainless steel plate sliding on the PTFE 

disc. 
SECTION 9: Inspection and Evaluation of Bridge Bearings 

TOPIC 9.1: Bridge Bearings 

9.1.17

Restraining Bearings Restraining bearings serve to hold a bridge down in the case of uplift. Uplift 

usually occurs on cantilever anchor spans. The devices used to resist uplift can be 

as simple as long bolts running through the bearings on short span bridges or as 

complex as chains of eyebars on larger structures. Lock nuts are used with bolted 

restraining devices to resist uplift. Pin and link members are also used as 

restraining devices. The type of restraining device used depends on the magnitude 

of the uplift force. 

Figure 9.1.19 Restraining Bearing 
SECTION 9: Inspection and Evaluation of Bridge Bearings 

TOPIC 9.1: Bridge Bearings 

9.1.18

 Pin and Link Bearings

The pin and link bearing is typically used on continuous cantilever structures to 

support the ends of a suspended span. It can also be used as a type of restraining 

device, which is discussed later in this topic. This bearing type consists of two 

vertically oriented steel plates pinned at the top and bottom to allow longitudinal 

movement. A disadvantage of this type of bearing is that, as the superstructure 

expands and contracts, the deck rises and falls (but only slightly). Another 

disadvantage is that pins can fracture when frozen by corrosion. 

Figure 9.1.20 Pin and Link Bearing
SECTION 9: Inspection and Evaluation of Bridge Bearings 

TOPIC 9.1: Bridge Bearings 

9.1.19

9.1.4 

Inspection 

Procedures 

When inspecting a bearing, the inspector must first determine if the bearing was 

initially intended to be fixed or expansion. If the bearing was designed to allow 

for translation or movement of the superstructure, then it is an expansion bearing; 

if not, then it is a fixed bearing. The inspector should refer to the design plans if 

available. It is critical that the inspector assess whether expansion bearings still 

allow for translation or horizontal movement. 

All bearings must have a suitable support. A distance of several inches should 

exist between the edge of the masonry plate and the edge of the supporting 

member, abutment, or pier. Note any loss to the supporting member near the 

bearing (e.g., spalling of a concrete bridge seat). 

Small maintenance problems with bearings can grow progressively worse if 

ignored, eventually causing major problems for the bridge. Inoperable bearings 

can transfer significant overstresses to the superstructure or substructure. 

Although there are many different types of bearings, bearing inspection can be 

broken down into two major categories based upon the basic materials from which 

they are made: 

3⁄4 Metal bearings 

3⁄4 Elastomeric bearings 

Various metallic materials have been used in bearings, including steel, bronze, 

aluminum, lead, and cast iron. However, steel is by far the most prominent and

also the most susceptible to deterioration, while the others mentioned are either 

non-corrosive or corrosion-resistant. Consequently, the following discussions will 

concentrate on the most common materials: steel bearings and elastomeric 

bearings. 
SECTION 9: Inspection and Evaluation of Bridge Bearings 

TOPIC 9.1: Bridge Bearings 

9.1.20

Inspection of Steel 

Bearings Inspection procedures to determine other causes of steel deterioration are 

discussed in detail in Topic 2.3.8. 

Visual Procedures 

The inspection of steel bridge members for defects is primarily a visual activity. 

Most defects in steel bridges are first detected by visual inspection. In order for 

this to occur, a hands-on inspection, or inspection where the inspector is close 

enough to touch the area being inspected, is required. More exact visual 

observations can also be employed using a magnifying unit after cleaning the paint 

from the suspect area. 

Physical Procedures 

Removal of paint can be done using a wire brush, grinding, or sand blasting, 

depending on the size of the suspected defect. The use of degreasing spray before 

and after removal of the paint may help in revealing the defect. 

When section loss occurs, use a wire brush, grinder or hammer to remove loose or 

flaked steel. After the flaked steel is removed, measure the remaining section and 

compare it to a similar section with no section loss. 

The usual and most reliable sign of fatigue cracks is the oxide or rust stains that 

develop after the paint film has cracked. Experience has shown that cracks have 

generally propagated to a depth between one-fourth and one-half the plate 

thickness before the paint film is broken, permitting the oxide to form. This 

occurs because the paint is more flexible than the underlying steel. 

Smaller cracks are not likely to be detected visually unless the paint, mill scale, 

and dirt are removed by carefully cleaning the suspect area. If the confirmation of 

a possible crack is to be conducted by another person, it is advisable not to disturb 

the suspected crack area so that re-examination of the actual conditions can be 

made. 

Once the presence of a fatigue crack has been verified, the inspector should 

examine all other similar locations and details. 

Advanced Inspection Techniques 

Several advanced techniques are available for steel inspection. 

Nondestructive methods, described in Topic 13.3.2, include: 

3⁄4 Acoustic emissions testing 

3⁄4 Computer tomography 

3⁄4 Corrosion sensors 

3⁄4 Smart paint 1 
SECTION 9: Inspection and Evaluation of Bridge Bearings 

TOPIC 9.1: Bridge Bearings 

9.1.21

3⁄4 Smart paint 2 

3⁄4 Dye penetrant 

3⁄4 Magnetic particle 

3⁄4 Radiographic testing 

3⁄4 Robotic inspection 

3⁄4 Ultrasonic testing (see Figure 9.1.21) 

3⁄4 Eddy current 

Other methods, described in Topic 13.3.3, include: 

3⁄4 Brinell hardness test 

3⁄4 Charpy impact test 

3⁄4 Chemical analysis 

3⁄4 Tensile strength test 

 Figure 9.1.21 UT Inspection of a Pin in a Bearing
SECTION 9: Inspection and Evaluation of Bridge Bearings 

TOPIC 9.1: Bridge Bearings 

9.1.22

Some inspection items are common to all steel bearings. For example, steel 

bearings are subject to the same corrosive forces as steel superstructures. 

Therefore, check all bearing elements for any significant section loss. 

Frozen bearings can occur when deterioration and debris buildup cause the bearing 

to bind up, thereby preventing free movement. Evidence of a frozen bearing 

includes bending, buckling, improper alignment of members, or cracks in the 

bearing or bearing seat. 

Bearings should be properly aligned horizontally and vertically, and the bearing 

surfaces should be clean and in full contact with each other. If only partial contact 

is made, damage can occur to the bearing device, superstructure, or substructure.

This damage can occur when a girder has moved horizontally so that the bearing

rests on only a portion of the masonry plate. The full load of the superstructure is 

therefore being applied to a smaller area on the masonry plate. This results in a 

higher stress that could crush the bridge seat. Also, such redistribution of the load 

may cause buckling to occur in the girder web of the superstructure above the 

bearing. 

 General Procedures 

Steel bearings should not be loose. Looseness can be identified by noise at the 

bearing or by visually detectable movement in the bearing when the bridge is 

subjected to live loads. Loosening can be caused by any of the following: 

3⁄4 Settlement or movement of the bearing support away from the portion of 

the bridge being supported 

3⁄4 Excessive rust or corrosion which results in a loss of material in the 

bearing itself 

3⁄4 Excessive deflection or vibration in the bridge 

3⁄4 Loose or missing fasteners that are used to attach the bearing to either the 

superstructure or the substructure 

3⁄4 Worn bearing elements 

3⁄4 Uplift in curved bridge superstructures 

3⁄4 Pavement pressure which drives the backwall into the beams 

Examine steel bearings for broken or cracked welds and missing or sheared 

fasteners. 

Bearings and the concrete substructure lateral shear keys on skewed bridges should 

be inspected for binding and damage due to the creep effect of the bridge (i.e., the 

tendency of the bridge to move laterally along the skew). 

Record the temperature during the inspection. Special thermometers with magnets 

are available to measure the actual temperature of the superstructure and bearing. 

Measure the movement of the bearings and compare it to the recorded temperature. 

The bearings should be in the expanded position when the temperature is greater 

then 68° F and in the contracted position when the temperature is less than 68° F. 

The following figures show examples of some common deficiencies in steel 

bearings. 
SECTION 9: Inspection and Evaluation of Bridge Bearings 

TOPIC 9.1: Bridge Bearings 

9.1.23

Figure 9.1.22 Heavy Corrosion and Excessive Movement on Steel Rocker 

Bearing 

Figure 9.1.23 Rocker Bearing with Excessive Horizontal Movement 
SECTION 9: Inspection and Evaluation of Bridge Bearings 

TOPIC 9.1: Bridge Bearings 

9.1.24

Figure 9.1.24 Spalling of Concrete Bridge Seat Due to High Edge Stress

Figure 9.1.25 Bent Anchor Bolt due to Excessive Horizontal Movement 
SECTION 9: Inspection and Evaluation of Bridge Bearings 

TOPIC 9.1: Bridge Bearings 

9.1.25

Figure 9.1.26 Uplift at Bridge Bearing

Specific inspection items for the various types of steel bearings are detailed in the 

following paragraphs. 

Sliding Plate Bearings

When a bridge is constructed, the upper and lower plates of the sliding plate 

bearing are placed such that they are centered with respect to each other at a 

certain temperature, usually 68°F. Any movement of the bearing can be measured 

based on this initial alignment. 

For plates of equal size, the amount of expansion or longitudinal movement that 

has occurred is the distance from the front or back of the top plate to the front or 

back of the bottom plate or, alternatively, the distance between the centers of the 

top and bottom plates. (See Figure 9.1.28). For plates of unequal size, the amount 

of expansion is one half of the difference between the front and back distances 

between the top and bottom plates. Alternatively, and perhaps easier to measure, 

the expansion is the distance between the centers of the top and bottom plates. 

These dimensions should be measured to the nearest 3 mm (1/8 inch), and the 

temperature at the time of inspection should be recorded. 

Bearings employing bronze sliding plates with steel masonry plates on bridges 
SECTION 9: Inspection and Evaluation of Bridge Bearings 

TOPIC 9.1: Bridge Bearings 

9.1.26

exposed to a salt air environment should be examined for signs of electrolytic 

corrosion between the bronze and steel plates. Electrolytic corrosion can also 

occur between aluminum and steel plates. 

See Figure 9.1.27 for a checklist of sliding plate bearing inspection items. 

Masonry

Pl.

Sole Pl.

C.L. Anchor

Bolt/Masonry Pl.

Check sliding surface

for corrosion and

freedom of movement.

Also, check for

complete contact.

C.L. Slotted Hole

Longitudinal

Movement

Check for bent or

loose anchor bolts.

Figure 9.1.27 Sliding Plate Bearing Inspection Checklist Items 

Figure 9.1.28 Longitudinal Misalignment in Bronze Sliding Plate Bearing
SECTION 9: Inspection and Evaluation of Bridge Bearings 

TOPIC 9.1: Bridge Bearings 

9.1.27

 Roller Bearings

Roller bearings are similar to sliding plate bearings in that the roller unit should be 

centered on the masonry plate at its design erection temperature. Therefore, the 

expansion (or contraction) is one half of the difference between the front of plateto-roller distance and the back of plate-to-roller distance (see Figure 9.1.29). 

Alternatively, and perhaps easier to measure, the expansion (or contraction) is also 

the distance between the center of the roller (where it contacts the masonry plate) 

and the center of the masonry plate. Again, the temperature at the time of 

inspection should be recorded. 

Rollers and masonry plates should be clean and free of corrosion in order to 

remain operable. They should be inspected for signs of wear. 

The position of the roller should also be examined to see if the pintles are exposed 

or missing. Such conditions may indicate excessive superstructure expansion or 

contraction movement or undesirable substructure movement. 

Figure 9.1.29 Damaged Roller Nest Bearing
SECTION 9: Inspection and Evaluation of Bridge Bearings 

TOPIC 9.1: Bridge Bearings 

9.1.28

 Rocker Bearings

See Figure 9.1.30 for a checklist of rocker bearing inspection items. 

Some rocker bearings have markings on the rocker and masonry plates. With no 

expansion or contraction, these marks should line up perfectly vertically. The 

amount of longitudinal movement can be determined by measuring the distance 

along the masonry plate between the two marks. 

If the bearing has no markings, the expansion can be determined by measuring the 

distance between the current point of contact between the rocker and the masonry 

plate and the original point of contact, which is assumed to be the midpoint along 

the rocker’s curved surface (see Figure 9.1.31). 

Measurements should be to the nearest 3 mm (1/8 inch), and the inspection 

temperature should be recorded. 

Rockers should be inspected for proper tilt. In warmer temperatures (above 68oF), 

the rockers should be tilted towards the backwall in the expanded direction; in 

colder temperatures, the rockers should be tilted backward in the contracted 

position away from the backwall (see Figure 9.1.30). Also check for the condition

of the pintles if they are visible. 

Rocker bearings and pins (if present) should be examined for corrosion, wear and 

freedom of movement (see Figure 9.1.32). 

Check the condition of the anchor bolts and nuts for corrosion and freedom of 

movement on expansion bearings. 

Figure 9.1.30 Rocker Bearing Inspection Checklist Items
SECTION 9: Inspection and Evaluation of Bridge Bearings 

TOPIC 9.1: Bridge Bearings 

9.1.29

Figure 9.1.31 Excessive Tilt in a Segmental Rocker 

Figure 9.1.32 Frozen Rocker Nest

 Pin and Link Bearings

Inspection of pin and link bearings is essentially the same as that described for 

pins and hangers in Topic 8.4. The amount of corrosion and ability of the 

connection to move freely is of critical concern, especially for suspended span 

bridges. 

The amount of corrosion on the pin and the interior portion of the link adjacent to 

it are impossible to detect visually. Ultrasonic testing or disassembly of the 

connection is required to determine the actual extent of deterioration. For a 
SECTION 9: Inspection and Evaluation of Bridge Bearings 

TOPIC 9.1: Bridge Bearings 

9.1.30

discussion of ultrasonic testing, refer to Topic 13.3. Since disassembly is 

impractical during normal periodic bridge inspections, the inspector must closely 

examine all exposed portions of the pin and link for signs of corrosion, wear, 

stress, cracks, bending, and misalignment. If warranted, the inspector should

recommend further action (i.e., special testing or disassembly of the pin and link). 

Also examine the hanger/link for proper amount of tilt using a plumb line or level, 

record the opening between the ends of the girders, and record the inspection 

temperature. 

Pot Bearings

Pot bearing longitudinal movement can be measured in the same way as for a 

sliding plate bearing. The movement is one half of the difference between the 

front and back distances of the top and bottom plates. If the pot bearing allows 

movement in two directions, the inspector should investigate transverse movement 

as well. The inspection temperature at which the measurements are taken should 

also be recorded. 

Although not normally required, pot bearing rotation should also be measured if it 

appears to be excessive. The top and bottom plates of a pot bearing are usually 

designed to be parallel if no rotation has taken place. Rotation can therefore be 

determined by measuring the length of the bottom plate and the distance between 

the two plates at the front and back of the bearing. The angle of rotation, 

measured from the horizontal, can be calculated using the following equation: 

Rotation (Degrees) = tan-1 [(Height1-Height2)/Plate Length] 

Figure 9.1.33 Angle of Rotation for Pot Bearing

Since the pot bearing allows multidirectional rotation, the inspector should check 

rotation along both sides of the bearing. 
SECTION 9: Inspection and Evaluation of Bridge Bearings 

TOPIC 9.1: Bridge Bearings 

9.1.31

Examine pot bearings for proper seating of the various elements with respect to 

one another. That is, check to see that the neoprene pad is properly seated within 

the pot and that the top plate is located properly over the elements below. 

Determine if the neoprene element is being extruded from the pot. Inspect guide 

bars for wear, binding, cracking and deterioration. 

Investigate welds for cracks, and examine for any separation between the PTFE 

and the steel surface to which it is bonded. Although they are usually hidden from 

view, check any exposed portions of the neoprene elements for splitting or tearing. 

Look for any buildup of dirt and debris in and around the bearing that would affect 

the smooth operation of the bearing. 

Restraining Bearings

Inspection of restraining bearings is very similar to that for pin and link bearings in 

that the condition of the main tension elements (i.e., hanger plates, eyebars, and 

anchor rods/bolts) and pins is the main concern. Where these elements encompass 

a normal bridge bearing, the inspection of the bearing assembly itself follows the 

procedures normally used for that particular type of bearing. 

The elements that make up the restraining portion of the bearing should be 

investigated for deterioration, misalignment, or other defects that could affect the 

normal operation of the bearing. Anchor bolts may need nondestructive testing to 

determine their condition. 

Inspection of Elastomeric 

Bearings 

Inspection of elastomeric bearings is somewhat simpler than the steel bearings 

since there are usually fewer elements to inspect. However, certain defects in 

elastomeric bearings are rather difficult to detect. Elements that are common to 

both steel bearings and elastomeric bearings are sole plates, masonry plates, and 

anchor bolts. Only the elastomeric elements or elements specific to elastomeric 

bearings will be discussed here. See Figure 9.1.34 for a checklist of elastomeric 

bearing inspection items. 

Neoprene Bearings

Neoprene bearing pads should be inspected for excessive bulging (approximately 

greater than 15% of thickness) (see Figure 9.1.35). This indicates that the bearing 

might be too tall for the application and therefore improperly designed. Slight 

bulging in the sides of the pad can be expected. Whether or not it is excessive may 

be difficult to determine, but if it appears excessive for the height/thickness of the 

pad, then it should be noted. As expansion and contraction of the structure takes 

place, the bulge will tend to roll on the beam or bridge seat. 

The bearing pad should be inspected for any splitting or tearing. Close attention 

should be paid to laminated neoprene bearings. Improper manufacturing can 

sometimes cause a failure in the area where the neoprene and interior steel shims 

are bonded together. 

The pad should also be inspected for variable thickness other than that attributable 

to normal rotation of the bearing. 

A plain (unlaminated) pad should be examined for any apparent growth in the 
SECTION 9: Inspection and Evaluation of Bridge Bearings 

TOPIC 9.1: Bridge Bearings 

9.1.32

length of the pad at the masonry plate. This growth indicates excessive strain in 

the pad. This is not a normal condition and usually indicates a problem with the 

design or manufacturing of the bearing. If this condition persists, the pad will 

eventually experience a shearing failure. Pad growth is not usually a problem with 

laminated bearings. 

Close attention should be given to the area where the pad is bonded to the sole and 

masonry plates. This is where a neoprene bearing frequently fails. Therefore, 

some agencies prohibit bonding of the bearing. Sometimes the pad tends to 

"walk" out from under the beam or girder. Some agencies prohibit painting of the 

contact surface between the neoprene and the sole plate for this reason. 

The longitudinal movement of a neoprene bearing pad is measured in nearly the 

same manner as for a sliding plate bearing. The longitudinal movement is the 

horizontal offset (in the longitudinal direction) between the top edge of the pad and 

the bottom edge of the pad. Record the temperature at the time of inspection. 

The rotation on a neoprene bearing is measured the same way as for a pot bearing. 

The top and bottom of the pad are normally parallel if no rotation has taken place. 

The inspector should measure the length of the pad and the height of the pad at the 

front and rear of the bearing. The equation presented in the pot bearing section 

can then be used to calculate the rotation. If a beveled pad is used to accommodate 

a bridge on grade, then the original dimensions of the pad must be known in order 

to determine the bearing rotation. 

Check for 

uniform 

thickness

Longitudinal 

Movement

Bearing Seat Check for excessive 

bulging, splitting or tearing

Figure 9.1.34 Elastomeric Bearing Inspection Checklist Items 
SECTION 9: Inspection and Evaluation of Bridge Bearings 

TOPIC 9.1: Bridge Bearings 

9.1.33

Figure 9.1.35 Neoprene Bearing Pad Excessive Bulging 

 Isolation Bearings

Isolation bearings are similar to neoprene bearing pads. They are composed of 

alternating layers of rubber and thin steel plates bonded together to form the 

bearing. A lead core is tightly fitted into a preformed hole to provide rigidity 

(under low lateral loads such as wind and braking forces) and energy dissipation 

(under seismic loads). These bearings also use steel dowels to transfer shear 

forces. 

The inspection items for isolation bearings are essentially the same as those for 

plain or laminated neoprene bearings. The only elements unique to isolation 

bearings are the lead core and steel dowels, both of which are hidden from view 

and can not be inspected. The lead core may yield during an earthquake. After a 

seismic event, the bearing shape and horizontal alignment in both the longitudinal 

and transverse direction must be closely inspected. It may be necessary to replace 

these bearings after an earthquake. 
SECTION 9: Inspection and Evaluation of Bridge Bearings 

TOPIC 9.1: Bridge Bearings 

9.1.34

Figure 9.1.36 Lead Core Isolation Bearing

9.1.5 

Evaluation State and federal rating guideline systems have been developed to aid in the 

inspection of bearings. The two major rating guideline systems currently in use 

are the FHWA's Recording and Coding Guide for the Structural Inventory and 

Appraisal of the Nation's Bridges used for the National Bridge Inventory (NBI) 

component rating method and the AASHTO element level condition state 

assessment method. 

NBI Rating Guidelines Using NBI rating guidelines, bearings fall under the superstructure on the Federal 

Structure Inventory and Appraisal (SI&A). The bearing type and the condition of 

the bearing are noted on the inspection form, but no rating is given. Some bridge 

owners do ask inspectors to provide a condition rating for bearings. The bearing 

condition does not influence the superstructure component rating, unless it is a 

serious condition. 

Element Level Condition 

State Assessment 

In an element level condition state assessment of a bridge bearing, the AASHTO 

CoRe element is one of the following, depending on the type: 

Element No. Description

310 Elastomeric Bearing 

311 Movable Bearing (roller, sliding, etc.) 

312 Enclosed / Concealed Bearing 

313 Fixed Bearing 

314 Pot Bearing 

315 Disk Bearing 

The unit quantity for the bearing elements is “each”, and each bearing element 

must be placed in one of the three available condition states based on the overall 

bearing condition. The inspector must note the condition of all the bearings 

individually and fit them into a given condition state description. Condition state 1 

is the best possible rating for the bearings. See the AASHTO Guide for Commonly 

Recognized (CoRe) Structural Elements for condition state descriptions. 
SECTION 9: Inspection and Evaluation of Bridge Bearings 

TOPIC 9.1: Bridge Bearings 

9.1.35

No Element Level Smart Flags are currently available for bearings. 

Serious Bearing 

Conditions 

Serious situations could be created for a bridge superstructure if horizontal failure 

of several bearings allows the superstructure to pull off the substructure. Failure 

of a tiedown (restraining) device which could allow a span to collapse and would 

also be considered a serious condition. 

If such a serious condition exists with the bearings, then the bearings have an 

impact on the superstructure condition rating. Otherwise, the bearings affect the 

superstructure rating very little. 

Figure 9.1.37 Serious Bearing Condition
SECTION 9: Inspection and Evaluation of Bridge Bearings 

TOPIC 9.1: Bridge Bearings 

9.1.36

Figure 9.1.38 Broken Pintle on a Bearing