12.1-i 

Table of Contents

Section 12 ..................................................................................................................................................

Special Bridges 

 12.1 Cable Supported Bridges ..................................................................... 12.1.1 

 

 12.1.1 Introduction............................................................................. 12.1.1 

 

 12.1.2 Design Characteristics............................................................. 12.1.2 

 Suspension Bridges .......................................................... 12.1.2 

 Cable-Stayed Bridges ...................................................... 12.1.2 

 Types of Cables ............................................................... 12.1.3 

 Corrosion Protection of Cables ....................................... 12.1.7 

 Types of Towers .............................................................. 12.1.8 

 12.1.3 Suspension Bridges................................................................. 12.1.9 

 Main Suspension Cables and Suspender Cables .............. 12.1.9 

 Cable Anchorages........................................................... 12.1.10 

 Cable Saddles ................................................................. 12.1.10 

 Suspender Cable Connections ........................................ 12.1.11 

 Vibrations ....................................................................... 12.1.12 

 

 12.1.4 Cable-Stayed Bridges............................................................ 12.1.14 

 Cable Arrangements and Systems .................................. 12.1.14 

 Cable Planes ................................................................... 12.1.16 

 Anchorages and Connections ......................................... 12.1.19 

 Vibrations ....................................................................... 12.1.21 

 

 12.1.5 Overview of Common Defects ............................................. 12.1.22 

 12.1.6 Inspection Locations and Procedures for Suspension Bridge Cable 

 System Elements................................................................ 12.1.22 

 Main Cable Anchorage Elements................................... 12.1.23 

 Main Suspension Cables................................................. 12.1.24 

 Saddles............................................................................ 12.1.25 

 Suspender Cables and Connections................................ 12.1.25 

 Sockets............................................................................ 12.1.25 

 Cable Bands.................................................................... 12.1.25 

 Recordkeeping and Documentation................................ 12.1.26 
SECTION 12: Special Bridges 

TOPIC 12.1: Cable Supported Bridges 

12.1-ii

 

 

 12.1.7 Inspection Locations and Procedures for Cable-Stayed Bridge 

 Cable System Elements ..................................................... 12.1.26 

 Inspection Elements........................................................ 12.1.28 

 Cable Wrapping.............................................................. 12.1.28 

 Cable Sheathing Assembly............................................. 12.1.29 

 Dampers.......................................................................... 12.1.31 

 Anchorages..................................................................... 12.1.35 

 Other Inspection Items ................................................... 12.1.36 

 Recordkeeping and Documentation................................ 12.1.37 

 

 12.1.8 Advanced Inspection Techniques ......................................... 12.1.37 

 12.1.9 Evaluation ............................................................................. 12.1.38 

 NBI Rating Guidelines ................................................... 12.1.38 

 Element Level Condition State Assessment................... 12.1.38 

 
12.1.1 

Section 12 

Special Bridges 

Topic 12.1 Cable Supported Bridges 

12.1.1 

Introduction There are several bridge types which feature elements which require special 

inspection procedures. The most notable bridge types are: 

3⁄4 Suspension bridges (see Figure 12.1.1) 

3⁄4 Cable-stayed bridges (see Figure 12.1.2) 

Figure 12.1.1 Golden Gate Bridge 
SECTION 12: Special Bridges 

TOPIC 12.1: Cable Supported Bridges 

12.1.2 

Figure 12.1.2 Maysville Cable-Stay Bridge, Built in 2000

This topic is limited to the cable and its elements. All other members of a cablesupported bridge have been described in earlier topics and should be referred to for 

the appropriate information. For each of the above bridge types, this topic 

provides: 

3⁄4 A general description 

3⁄4 Identification of special elements 

3⁄4 An inspection procedure for special elements 

3⁄4 Methods of recordkeeping and documentation

12.1.2 

Design 

Characteristics 

A cable-supported bridge is a bridge that is supported by or “suspended from”

cables. 

Suspension Bridge A suspension bridge has a deck, which is supported by vertical suspender cables 

that are in turn supported by main suspension cables. The suspension cables are 

supported by saddles atop towers and are anchored at their ends. Suspension 

bridges are normally constructed when intermediate piers are not feasible because 

of long span requirements (see Figure 12.1.3). Modern suspension bridge spans 

are generally longer than 427 m (1400 feet). 

Cable-Stayed Bridge A cable-stayed bridge is another long span cable supported bridge where the 

superstructure is supported by cables, or stays, passing over or anchored to towers 

located at the main piers. Cable-stayed bridges are the more modern version of 

cable-supported brides. Spans generally range from 213 to 427 m (700 to 1400 

feet) (see Figure 12.1.4). Evolving for approximately 400 years, the first vehicular 

cable-stayed bridge in the United States was constructed in Alaska in 1972 (John 

O'Connell Memorial Bridge at Sitka, Alaska). 

In suspension bridges, vertical suspender cables attach the deck to the loosely hung 
SECTION 12: Special Bridges 

TOPIC 12.1: Cable Supported Bridges 

12.1.3 

main cables. Cable-stayed bridges are much stiffer than suspension bridges. In 

cable-stayed bridges, the deck is supported directly from the tower with fairly taut 

stay cables. 

Figure 12.1.3 Roebling Bridge 

Figure 12.1.4 Sunshine Skyway Cable-Stayed Bridge in Tampa Bay, Florida 

Types of Cables A cable may be composed of one or more structural wire ropes, structural wire 

strands, locked coil strands, parallel wire strands, or parallel wires. 

Parallel Wire Cable 

Parallel wire cable consists of a number of parallel wires. Size varies (see Figure 
SECTION 12: Special Bridges 

TOPIC 12.1: Cable Supported Bridges 

12.1.4 

12.1.5). Parallel wire cables used in cable-stayed bridges conforms to ASTM 

A421, Type BA, low relaxation. It is basically stress-relieved wire used for 

prestressed concrete. Corrosion protection consists of polyethylene sheathing 

filled with cement grout. The tubing is usually wrapped with polyvinyl film tape 

(see Figure 12.1.5). 

Structural Wire Strand 

Structural wire strand is an assembly of wires formed helically around a center 

wire in one or more symmetrical layers. Sizes normally range from 50 to 100 mm 

(2 to 4 inches) (see Figure 12.1.6). 

Structural Wire Rope 

Structural wire rope is an assembly of strands formed helically around a center 

strand (see Figure 12.1.7). 

Parallel Strand Cable 

Parallel strand cable is a parallel group of strands (see Figure 12.1.8). Seven-wire 

strand commonly used for cable-stayed bridges conforms to ASTM A416, weld 

less and low relaxation (see Figure 12.1.11). It is basically seven-wire stressrelieved strand for prestressed concrete. The corrosion protection system used for 

the seven-wire strand cables is similar to the system used for the parallel wire 

cables. 

Locked Coil Strand 

Locked coil strand is a helical type strand composed of a number of round wires, 

and then several layers of wedge or keystone shaped wires and finally several 

layers of Z- or S-shaped wires (see Figure 12.1.9). Locked coil strand has not been 

used for cable-stayed bridges in this country, but it is commonly used for cablestayed bridges in Europe. 

Several types of cables have been used for cable-stayed bridges. The three most 

common are locked-coil strand, parallel wire, and parallel seven-wire strand. The 

majority of existing cable-stayed bridges in the world, other than the United States, 

use preformed prestretched galvanized locked-coil strand. The cable-stayed 

bridges in the United States incorporate parallel wire or seven-wire prestressing 

strand in the cables, which are protected in a polyethylene tube filled with cement 

grout. The tube is commonly wrapped with a polyvinyl film. 
SECTION 12: Special Bridges 

TOPIC 12.1: Cable Supported Bridges 

12.1.5 

Figure 12.1.5 Parallel Wire 

Figure 12.1.6 Structural Wire Strand 

Figure 12.1.7 Structural Wire Rope 

Figure 12.1.8 Parallel Strand Cable 
SECTION 12: Special Bridges 

TOPIC 12.1: Cable Supported Bridges 

12.1.6 

Figure 12.1.9 Locked Coil Strand Cross-Section 

Figure 12.1.10 Parallel Wire 
SECTION 12: Special Bridges 

TOPIC 12.1: Cable Supported Bridges 

12.1.7 

Figure 12.1.11 Parallel Strand 

Corrosion Protection of 

Cables 

Methods used for corrosion protection include: 

 

3⁄4 galvanizing the individual wires 

3⁄4 painting the finished cable 

3⁄4 wrapping the finished cable with spirally wound soft galvanized wire, 

neoprene, or plastic wrap type tape 

3⁄4 any combination of the above systems (see Figure 12.1.12). 

Figure 12.1.12 Cable Wrapping on the Wheeling Suspension Bridge 
SECTION 12: Special Bridges 

TOPIC 12.1: Cable Supported Bridges 

12.1.8 

Types of Towers 3⁄4 Portal tower 

3⁄4 A-frame tower 

3⁄4 Single tower 

Towers are constructed of reinforced concrete or steel or a combination of the two 

(see Figures 12.1.13 and 12.1.14). 

Figure 12.1.13 Tower Types: Concrete “Portal Tower” and “A-Frame Tower” 

Figure 12.1.14 Tower Types: Steel “Portal Tower” and Concrete “A-Frame 

Tower” 

The deck structures are also constructed of concrete or steel. 
SECTION 12: Special Bridges 

TOPIC 12.1: Cable Supported Bridges 

12.1.9 

12.1.3 

Suspension Bridges In this subtopic, only those bridge elements that are unique to suspension bridges 

are described. Refer to the appropriate topic for other bridge elements that are 

common to most bridges. 

Main Suspension Cables 

and Suspender Cables 

Main suspension cables are generally supported on saddles at the towers and are 

anchored at each end. Suspender cables are vertical cables that connect the deck 

system to the main cables (see Figure 12.1.15). The main cables are commonly 

composed of a number of parallel wires banded together and wrapped with a soft 

wire wrapping. Composition of the suspender cables varies. 

Figure 12.1.15 Three-Span Suspension Bridge Schematic 

If a suspension bridge has only two main suspension cables, the cables are 

considered as fracture critical members. This is due to the non-redundancy (only 

two load paths) of the main suspension cables. Refer to Topic 8.1 for a detailed 

description of fracture criticality and redundancy. 
SECTION 12: Special Bridges 

TOPIC 12.1: Cable Supported Bridges 

12.1.10 

Cable Anchorages In bridges with common earth anchored cable systems, either above or below 

ground, the total force of the main cable has to be transferred into the anchor block 

(see Figure 12.1.16). The void area inside the anchor block is referred to as the 

Chain Gallery. The force from the main cable is distributed through the splay 

saddle, bridge wires, strand shoes and anchor bars. The anchor bars are embedded 

and secured in the concrete of the anchor block. The anchor bars may consist of 

steel bars, rods, pipes, or prestressed bars / strands. 

Splay Saddle

Bridge Wires

Strand Shoes

Anchor Bars

in Concrete

Chain Gallery Soft Wire Wrapping

Gravity Anchor

(Spun-in-place Strands)

Figure 12.1.16 Anchor Block Schematic 

Cable Saddles The connection between main cable and tower is usually made through saddles. 

The saddle supports the main cable as it crosses over the tower. Saddles are 

commonly made from fabricated steel or castings (see Figure 12.1.17). 

Figure 12.1.17 Cable Saddles for the Manhattan Bridge, NYC (Main Span 451.1 

m (1,480 ft)) 
SECTION 12: Special Bridges 

TOPIC 12.1: Cable Supported Bridges 

12.1.11 

Suspender Cable 

Connections 

The connection between the main and suspender cable is made by means of a 

cable band. The cable band consists of two semi-cylindrical halves connected by 

high-tensile steel bolts to develop the necessary friction. 

Grooved cable bands have been used in the majority of suspension bridges (see 

Figure 12.1.18). The top surfaces of the bands are grooved to receive the 

suspender cables, which are looped over the band. 

Instead of looping the hanger cables around the band, the hanger might also be 

socketed at the upper end and pin connected to the cable band. This connection is 

called an open socket (see Figure 12.1.19). Connection to the deck and floor 

system can also be a similar open socket arrangement or it can be connected 

directly to a girder - similar to the tied arch bridge.

Figure 12.1.18 Grooved Cable Bands 

Figure 12.1.19 Open Socket Suspender Cable Connection 
SECTION 12: Special Bridges 

TOPIC 12.1: Cable Supported Bridges 

12.1.12 

Vibrations The flexibility of cable supported structures, associated with high stress levels in 

the main load carrying members, makes these structures especially sensitive to 

dynamic forces caused by earthquake, wind, or vehicular loads. The inspector 

should always note and describe vibrations whether local or global, while 

performing inspections of cable-supported structures. The term local vibration is 

used when dealing with the vibration in an individual member (see Figure 

12.1.20). When the vibration of the entire structure as a whole is analyzed, it is 

known as global vibration (see Figure 12.1.21). Due to the amount of vibration in 

cable supported structures, it may be common to see various types of damping 

systems attached to cables. Damping systems may be a tie between two cables, 

neoprene cushions, shock absorbers mounted directly to the cables, or other 

systems that act to dampen the cable vibrations (see figures 12.1.22 and 12.1.23). 

Figure 12.1.20 Cable Vibrations Local System Schematic 

Figure 12.1.21 Cable Vibrations Global System Schematic 

Vibrations can affect suspension cables in several ways. Vibration opens cable 

wires allowing entry of corrosive chemicals and accelerates corrosion. Vibrations 

create fretting, cracks grout, and accelerate fatigue. 
SECTION 12: Special Bridges 

TOPIC 12.1: Cable Supported Bridges 

12.1.13 

Figure 12.1.22 Wheeling Suspension Bridge – Cable Damping System (Photo 

Courtesy of Geoffrey H. Goldberg, 1999) 

Figure 12.1.23 Cable Tie Damper System 
SECTION 12: Special Bridges 

TOPIC 12.1: Cable Supported Bridges 

12.1.14 

12.1.4 

Cable-Stayed 

Bridges 

Only the cable and its elements are described in this subtopic. Refer to the 

appropriate topic for detailed descriptions of other bridge members that are 

common to most structures. 

Due to the complexity of the various cable arrangements and systems, fracture 

criticality for individual cable-stayed structures can only be determined through a 

detailed structural analysis. 

Cable Arrangements and 

Systems 

Cable-stayed bridges may be categorized according to the various longitudinal 

cable arrangements. These cable arrangements can be divided into the following 

four basic systems: 

3⁄4 Radial or Converging Cable System 

3⁄4 Harp Cable System 

3⁄4 Fan Cable System 

3⁄4 Star Cable System 

Radial or Converging Cable System 

In this system, all cables are leading to the top of the tower at a common point. 

Structurally, this arrangement is the most effective. By anchoring all the cables to 

the tower top, the maximum inclination to the horizontal is achieved (see Figure 

12.1.24). 

Figure 12.1.24 Radial or Converging Cable System Schematic 
SECTION 12: Special Bridges 

TOPIC 12.1: Cable Supported Bridges 

12.1.15 

Harp Cable System 

The harp system, as the name implies, resembles harp strings. In this system, the 

cables are parallel and equidistant from each other. The cables are also spaced 

uniformly along the tower height and connect to the deck superstructure at the 

same spacing (see Figure 12.1.25). 

Figure 12.1.25 Harp or Parallel Cable System Schematic 

Fan Cable System 

The fan system is a combination of the radial and the harp systems. The cables 

emanate from the top of the tower at equal spaces and connect to the 

superstructure at larger equal spaces (see Figure 12.1.26). 

Figure 12.1.26 Fan or Intermediate Cable System Schematic 
SECTION 12: Special Bridges 

TOPIC 12.1: Cable Supported Bridges 

12.1.16 

Star Cable System 

In the star system, the cables intersect the tower at different heights and then 

converge on each side of the tower to intersect the deck structure at a common 

point. The common intersection in the anchor span is usually located over the 

abutment or end pier. The star system is rather uncommon. The star system 

requires a much stiffer deck structure since the cables are not distributed along the 

deck (see Figure 12.1.27). 

Figure 12.1.27 Star Cable System Schematic 

Cable Planes The cables may lie in either a single or a double plane, may be symmetrical or 

asymmetrical, and may lie in oblique or vertical planes. 

Single Plane 

The single-plane cable arrangement is used with a divided deck structure with the 

cables passing through the median area and anchored below the roadway. A 

single-plane cable system generally utilizes single towers (see Figure 12.1.28). 

Figure 12.1.28 Single Vertical Plane Cable System 
SECTION 12: Special Bridges 

TOPIC 12.1: Cable Supported Bridges 

12.1.17 

Double Vertical Plane 

The double vertical plane system incorporates two vertical cable planes connecting 

the tower to the edge girders along the deck structure. The structure may utilize 

twin towers or a portal frame tower (see Figure 12.1.29). The portal frame tower 

is a twin tower with a connecting strut at the top. Wider bridges may utilize a 

triple plane system that is basically a combination of the single and double plane 

systems. 

Figure 12.1.29 Double Vertical Plane Cable System 
SECTION 12: Special Bridges 

TOPIC 12.1: Cable Supported Bridges 

12.1.18 

Double Inclined Plane 

In this two plane system the cable planes are oblique, sloping toward each other 

from the edges of the roadway and intersecting at the tower along the longitudinal 

centerline of the deck (see Figure 12.1.30). Generally the tower is an A-frame 

type, receiving the sloping cables that intersect close to the roadway centerline on 

the tower. 

Figure 12.1.30 Double Inclined Plane Cable System 
SECTION 12: Special Bridges 

TOPIC 12.1: Cable Supported Bridges 

12.1.19 

Anchorages and 

Connections 

The cables may be continuous and pass through or over the tower or be terminated 

at the tower. If continuous across the tower, a saddle is incorporated. 

Saddles 

The cable saddles may be constructed from fabricated plates or steel castings with 

grooves through which the cables pass (see Figure 12.1.31). Between the end and 

center spans differential forces will occur at the cable saddles unless they are 

supported by rollers or rocker bearings. When the saddles are fixed, the rigidity of 

the system is at a maximum. 

Figure 12.1.31 Cable Saddle 
SECTION 12: Special Bridges 

TOPIC 12.1: Cable Supported Bridges 

12.1.20 

End Fittings 

If terminated at the tower, an end fitting or anchorage is incorporated. A similar 

end fitting is utilized at the deck (see Figure 12.1.32). 

Figure 12.1.32 Cable Deck Anchorage 

Socket 

A socket widely used for the anchoring of parallel-wire strands is a poured zinc 

socket. The wires are led through holes in a locking plate at the end of the socket 

and have the bottom heads providing the resistance against slippage of wires. The 

cavity inside the socket is filled with hot zinc alloys. To improve the fatigue 

resistance of the anchor, a cold casing material is used. 

Figure 12.1.33 Anchor Inspection on Veterans Bridge 
SECTION 12: Special Bridges 

TOPIC 12.1: Cable Supported Bridges 

12.1.21 

The problems encountered with low fatigue strength of zinc-poured sockets lead to 

the development of HiAm sockets in 1968 for use with parallel wire stays. 

This anchorage incorporates a flat plate with countersunk radial holes to 

accommodate the geometry of flared wires that transition from the compact wire 

bundle into the anchorage. The anchorage socket is filled with zinc dust and with 

an epoxy binder. This method of anchoring the stays increases the magnitude of 

fatigue resistance to almost twice that for the zinc-poured sockets. 

A common anchorage type for strands is the Freyssinet type anchor. 

In the Freyssinet socket the seven wire strand is anchored to an anchor plate using 

wedges similar to prestressing wedges. This wedge anchor is used during 

erection. After application of dead load the anchor tube is filled with an epoxy 

resin, zinc dust, and steel ball composition. Under live load, the additional cable 

force will be transformed by shear from the cable strand to the tube. 

Vibrations Cable stay bridges experience vibrations similar to suspension bridges. Several of 

the primary causes of vibration in stay cables consist of rain-wind induced 

vibrations, sympathetic vibration of cables with other bridges elements excited by 

wind, inclined cable galloping, and vortex excitation of single cable or groups of 

cables. The inspector should always note and describe vibrations whether local or 

global, while performing inspections of cable-supported structures. Due to the 

amount of vibration in cable supported structures, it may be common to see 

various types of damping systems attached to cables. Damping systems may be a 

tie between two cables, neoprene cushions, shock absorbers mounted directly to 

the cables, or other systems that act to dampen the cable vibrations (see Figure 

12.1.34). 

Vibrations can affect stay cables in several ways. Vibration opens cable wires 

allowing entry of corrosive chemicals and accelerates corrosion. Vibrations create 

fretting, cracks grout, and accelerate fatigue. 

Figure 12.1.34 Damper on Cable Stayed Bridge 
SECTION 12: Special Bridges 

TOPIC 12.1: Cable Supported Bridges 

12.1.22 

12.1.5 

Overview of 

Common Defects 

Common defects that can occur on the cable members of a cable-supported bridge 

include: 

3⁄4 Failure of the Paint System 

3⁄4 Pitting 

3⁄4 Surface Rust 

3⁄4 Section Loss 

3⁄4 Fatigue Cracking 

3⁄4 Collision Damage 

3⁄4 Overload Damage 

3⁄4 Heat Damage 

Refer to Topic 2.3 for a more detailed presentation of the properties of steel, types 

and causes of steel deterioration, and the examination of steel. 

12.1.6 

Inspection 

Locations and 

Procedures for 

Suspension Bridge 

Cable System 

Elements 

The inspection and maintenance procedures presented in this Topic are not 

exhaustive, but are unique to the particular bridge type. Therefore, the inspection 

of special bridges should include both those procedures presented in this Topic and 

the general procedures presented previously in this manual. 

These bridges are considered to be complex according to the NBIS regulations. 

The NBIS requires identification of specialized inspection procedures, and 

additional inspector training and experience required to inspect these complex 

bridges. The bridges are then to be inspected according to these procedures. 

Due to the specialized nature of these bridges and because no two cable supported 

bridges are identical, the inspection should be led by someone very familiar with 

the particular bridge. Many major bridges, such as cable supported bridges, will 

have individual maintenance manuals developed specifically for that bridge, like 

an "owner's" manual. If available, the inspector should use this valuable tool 

throughout the inspection process and should verify that specified routine 

maintenance has been performed. Customized, preprinted inspection forms should 

be used wherever possible to enable the inspector to report the findings in a 

rigorous and systematic manner. 
SECTION 12: Special Bridges 

TOPIC 12.1: Cable Supported Bridges 

12.1.23 

Main Cable Anchorage 

Elements 

The anchorage system, at the ends of the main cables, consists of a number of 

elements that require inspection (see Figure 12.1.35). 

3⁄4 Splay saddle 

3⁄4 Bridge Wires 

3⁄4 Strand shoes or sockets 

3⁄4 Anchor bars 

3⁄4 Chain Gallery 

Splay Saddle

Bridge Wires

Strand Shoes

Anchor Bars

in Concrete

Chain Gallery Soft Wire Wrapping

Gravity Anchor

(Spun-in-place Strands)

Figure 12.1.35 Anchor Block Schematic 

Splay Saddle 

Inspect the splay saddles for missing or loose bolts and the presence of cracks in 

the casting itself. Movement up the cable away from the splay; signs of this 

movement may be the appearance of unpainted strands on the lower side or 

“bunched up” wrapping on the upper side 

Wires in Anchorage 

In parallel wire type suspension bridges, inspect the unwrapped wires between the 

strand shoes and the splay saddle. Carefully insert a large screwdriver between the 

wires and apply leverage. This will help reveal broken wires. Inspect the wires for

abrasion damage, corrosion, and movement. 

Strand Shoes or Sockets 

At the anchorages of parallel wire type suspension bridges, inspect the strand shoes 

for signs of displaced shims, along with movement, corrosion, misalignment, and 

cracks in the shoes. 

At the anchorages of prefabricated strand type suspension bridges, inspect the 
SECTION 12: Special Bridges 

TOPIC 12.1: Cable Supported Bridges 

12.1.24 

strand sockets for signs of movement, slack or sag, corrosion, and broken sockets. 

Unpainted or rusty threads at the face of the sockets may indicate possible 

“backing off” of nuts. 

Anchor Bars 

Inspect the anchor bars or rods for corrosion (section loss), deterioration, or 

movement at the face of their concrete embedment. Check for corrosion or other 

signs of distress over the entire visible (unencased) portion. 

Anchorage Interior 

Inspect the interior of the anchorage for corrosion and deterioration of any steel 

hardware, and cracks and spalls in the concrete anchor. Note if there is protection 

against water entering or collecting where it may cause corrosion, and also if there 

is proper ventilation (see Figure 12.1.36). 

Figure 12.1.36 Anchorage Interior of Ben Franklin Bridge 

Main Suspension Cables The main suspension cables should be inspected as follows: 

Locations 

Inspect the main suspension cables for indications of corroded wires. Inspect the 

condition of the protective covering or coating, especially at low points of cables, 

areas adjacent to the cable bands, saddles over towers, and at anchorages. 

Cable Wrapping 

Inspect the wrapping wire for cracks, staining, and dark spots. Check for loose 
SECTION 12: Special Bridges 

TOPIC 12.1: Cable Supported Bridges 

12.1.25 

wrapping wires. If there are cracks in the caulking where water can enter, this can 

cause corrosion of the main suspension cable. Check for evidence of water 

seepage at the cable bands, saddles, and splay castings (see Figure 12.1.37). 

Figure 12.1.37 Tape and Rubber Seal Torn Around Cable Allowing Water 

Penetration into Top of Sheath 

Hand Ropes 

Inspect the hand ropes and connections along the main cables for loose 

connections of stanchion to cable bands or loose connections at anchorages or 

towers. Check also for corroded or deteriorated ropes or stanchions, bent or 

twisted stanchions (hand rope supports), and too much slack in rope. 

Vibration 

Note and record all excessive vibrations.

Saddles Inspect the saddles for missing or loose bolts, and corrosion or cracks in the 

casting. Check for proper connection to top of tower or supporting member and 

possible slippage of the main cable. 

Suspender Cables and 

Connections 

Inspect the suspender cables for corrosion or deterioration, broken wires, and kinks 

or slack. Check for abrasion or wear at sockets, saddles, clamps, and spreaders. 

Be sure to note excessive vibrations. 

Sockets Inspect the suspender rope sockets for corrosion, cracks, or deterioration 

3⁄4 Abrasion at connection to bridge superstructure 

3⁄4 Possible movement 

Cable Bands Inspect the cable bands for missing or loose bolts, or broken suspender saddles. 

Signs of possible slippage are caulking that has pulled away from the casting or 
SECTION 12: Special Bridges 

TOPIC 12.1: Cable Supported Bridges 

12.1.26 

“bunching up” of the soft wire wrapping adjacent to the band. Check for the 

presence of cracks in the band itself, corrosion or deterioration of the band, and 

loose wrapping wires at the band. 

Recordkeeping and 

Documentation 

A set of customized, preprinted forms should be prepared for documenting all 

defects encountered in the cable system of a suspension bridge. A suggested 

sample form is presented in Figure 12.1.38. A separate form should be used for 

each main suspension cable. Designations used to identify the suspender ropes and 

the panels provide a methodology for locating the defects in the structure. 

 1

4

8

14

17

ANCHORAGE NO.1 ANCHORAGE NO.2 

TOWER NO.1 TOWER NO.2

SUSPENDER CABLE CONDITION

1. 7. 13.

2. 8. 14.

3. 9. 15.

4. 10. 16.

5. 11. 17.

6. 12.

SUSPENSION BRIDGE

Figure 12.1.38 Form for Recording Defects in the Cable System of a Suspension 

Bridge 

12.1.7 

Inspection 

Locations and 

Procedures for 

Cable-Stayed 

Bridge Cable 

System Elements 

A cable-stayed bridge is a bridge in which the superstructure is supported by 

cables, or stays, passing over or attached directly to towers located at the main 

piers (see Figure 12.1.39 and 12.1.40). There are several special elements that are 

unique to cable-stayed bridges, and the bridge inspector should be familiar with 

them. 

See the National Cooperative Highway Research Program (NCHRP) Synthesis 353 

“Inspection and Maintenance of Bridge Cable Systems”, 2005 for a detailed 

description of inspection locations and procedures for cable-stayed bridge cable 

element systems. 

These bridges are considered to be complex according to the NBIS regulations. 

The NBIS requires identification of specialized inspection procedures, and 

additional inspector training and experience required to inspect these complex 

bridges. The bridges are then to be inspected according to these procedures. 
SECTION 12: Special Bridges 

TOPIC 12.1: Cable Supported Bridges 

12.1.27 

Figure 12.1.39 Cable-Stayed Bridge 

Figure 12.1.40 Cable-Stayed Bridge Cables 
SECTION 12: Special Bridges 

TOPIC 12.1: Cable Supported Bridges 

12.1.28 

Inspection Elements The inspection of the cable elements should include: 

 

3⁄4 Cable wrappings and wrap ends near the tower and deck 

3⁄4 Cable sheathing assembly 

3⁄4 Dampers 

3⁄4 Anchorages

Cable Wrapping Common wrapping methods for corrosion protection of finished cables include 

spirally wound soft galvanized wire, neoprene, or plastic wrap type tape (see 

Figure 12.1.41). The wrappings should be inspected for corrosion and cracking of 

soft galvanized wire, staining and dark spots indicating possible corrosion of the 

cables, and loose wrapping wires or tape. Bulging or deforming of wrapping 

material may indicate possible broken wire (see Figure 12.1.42). Check for 

evidence of water seepage at the cable bands, saddles, and splay castings. 

Figure 12.1.41 Cable Wrapping Placement 
SECTION 12: Special Bridges 

TOPIC 12.1: Cable Supported Bridges 

12.1.29 

Figure 12.1.42 Investigation of Deformed Cable Wrapping 

Cable Sheathing 

Assembly 

The most common types of cable sheathing assemblies are steel sheathing and 

polyethylene sheathing. 

Steel Sheathing 

If steel sheathing is used, inspect the system for corrosion (see Figure 12.1.43), 

condition of protective coatings, and weld fusion. Bulging may indicate broken 

wires (see Figure 12.1.44). Splitting may be caused by water infiltration and 

corrosive action. Cracking is sometimes caused by fatigue (see Figure 12.1.45). 

Polyethylene Sheathing 

If polyethylene sheathing is used, inspect the system for nicks, cuts, and abrasions. 

Check for cracks and separations in caulking and in fusion welds. Bulging may 

indicate broken wires (see Figure 12.1.44). Splitting is sometimes caused by 

temperature fluctuations (see Figure 12.1.46). Coefficient of the thermal 

expansion for polyethylene is three times higher than the value for steel or 

concrete. Cracking is sometimes caused by fatigue.
SECTION 12: Special Bridges 

TOPIC 12.1: Cable Supported Bridges 

12.1.30 

Figure 12.1.43 Corrosion of Steel Sheathing 

Figure 12.1.44 Bulging of Cable Sheathing 
SECTION 12: Special Bridges 

TOPIC 12.1: Cable Supported Bridges 

12.1.31 

Figure 12.1.45 Cracking of Cable Sheathing 

Figure 12.1.46 Splitting of Cable Sheathing 

Dampers Shock Absorber Type 

A variety of damper types may have been installed (see Figure 12.1.47 and 

12.1.48). If shock absorber type dampers are used, inspect the system for

corrosion, oil leakage in the shock absorbers, and deformations in the bushings. 

Check for tightness in the connection to the cable pipe, and torque in the bolts. 
SECTION 12: Special Bridges 

TOPIC 12.1: Cable Supported Bridges 

12.1.32 

Figure 12.1.47 Shock Absorber Damper System 

Figure 12.1.48 Shock Absorber Damper System 
SECTION 12: Special Bridges 

TOPIC 12.1: Cable Supported Bridges 

12.1.33 

Tie Type 

Inspect the tie type dampers (see Figure 12.1.49) for corrosion, and deformations 

in the bushings. Check for tightness in the connection to the cable pipe, and torque 

in the bolts.

Figure 12.1.49 Cable Tie Type Damper System 
SECTION 12: Special Bridges 

TOPIC 12.1: Cable Supported Bridges 

12.1.34 

Tuned Mass Type 

Inspect the tuned mass dampers (see Figure 12.1.50) for corrosion, and

deformations in the bushings. Check for tightness in the connection to the cable 

pipe, and torque in the bolts.

Figure 12.1.50 Tuned Mass Damper System 
SECTION 12: Special Bridges 

TOPIC 12.1: Cable Supported Bridges 

12.1.35 

Anchorages End Anchorage 

Inspect the transition area between the steel anchor pipe and cable for water 

tightness of neoprene boots at the upper ends of the steel guide pipes (see Figure 

12.1.51). Check for drainage between the guide pipe and transition pipe, and 

defects, such as splits and tears, in the neoprene boots (see Figure 12.1.52). Check 

for sufficient clearance between the anchor pipe and cable, noting rub marks and 

kinks.

Figure 12.1.51 Neoprene Boot at Steel Anchor Pipe Near Anchor 

Figure 12.1.52 Split Neoprene Boot 
SECTION 12: Special Bridges 

TOPIC 12.1: Cable Supported Bridges 

12.1.36 

Tower Anchorage 

Inspect the cable anchorages for corrosion of the anchor system (see Figure 

12.1.53). Check for cracks and nut rotation at the socket and bearing plate, and 

seepage of grease from the protective hood. 

Figure 12.1.53 Corrosion of the Anchor System 

Other Inspection Items The inspection of the cable system should also include anchor pipe clearances, 

flange joints, and polyethylene expansion joints. Read the load cells and record 

the forces in the cables. Note and record all excessive vibrations including 

amplitude and type of vibration along with wind speed and direction, or other 

forces including vibrations such as traffic. Cable lighting should also be evaluated. 
SECTION 12: Special Bridges 

TOPIC 12.1: Cable Supported Bridges 

12.1.37 

Recordkeeping and 

Documentation 

A set of customized, preprinted forms should be prepared for documenting all 

defects encountered in the cable system of a cable-stayed bridge. A suggested 

sample form is presented in Figure 12.1.54. A separate form should be used for 

each plane or set of cables. Designations used to identify the cables and the panels 

provide a methodology for locating the defects in the structure. 

 1

ABUTMENT 

NO.1

ABUTMENT 

NO.2

PIERS

CABLE CONDITION

1. 5.

2. 6.

3. 7.

4. 8.

CABLE-STAYED BRIDGE

2 8 3 4 5 6 7

Figure 12.1.54 Form for Recording Defects in Cable System of a Cable-Stayed 

Bridge 

12.1.8 

Advanced 

Inspection 

Techniques 

In bridge cables, whether a suspension bridge or cable-stayed bridge, the greatest 

problems generally occur due to corrosion and fracture of individual wires. Visual 

inspection of unwrapped cables is limited to the outer wires, while visual 

inspection of wrapped cables is limited to the protective sheathing. Therefore, 

advanced inspection techniques should be used to achieve a more rigorous and 

thorough inspection of the cables, including: 

3⁄4 Magnetic induction 

3⁄4 Electrical resistivity 

3⁄4 Dye penetrant 

3⁄4 Ultrasonic testing 

3⁄4 Radiographic testing 

3⁄4 Acoustic emission 

3⁄4 Accelerometers 

3⁄4 Strain measurements 

3⁄4 Vibration measurements 

3⁄4 Magnetic flux leakage 

3⁄4 Impulse radar 

3⁄4 Laser vibrometer 
SECTION 12: Special Bridges 

TOPIC 12.1: Cable Supported Bridges 

12.1.38 

3⁄4 Infrared thermography 

3⁄4 Measurement of loads 

3⁄4 Measurement of stress ranges 

See Topic 13.3 for Advanced Inspection Techniques for steel. 

12.1.9 

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

inspection of steel superstructures. 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 the NBIS rating guidelines, a 1-digit code on the Federal Structure Inventory 

and Appraisal (SI&A) sheet indicates the condition of the superstructure. Rating 

codes range from 9 to 0 where 9 is the best rating possible. See Topic 4.2 (Item 

59) for additional details about NBIS Rating Guidelines. 

The previous inspection data should be considered along with current inspection 

findings to determine the correct rating. 

Element Level Condition 

State Assessment 

In an element level condition state assessment of a cable-supported bridge, the 

AASHTO CoRe element is: 

Element No. Description

146 Unpainted Steel Cable (not embedded in concrete) 

147 Painted Steel Cable (not embedded in concrete) 

The unit quantity for cables is each and the total number of cables must be placed 

in one of the four available condition states for unpainted and five available 

condition states for painted. In both cases, Condition State 1 is the best possible 

rating. See the AASHTO Guide for Commonly Recognized (CoRe) Structural 

Elements for condition state descriptions. 

A Smart Flag is used when a specific condition exists, which is not described in 

the CoRe element condition state. The severity of the damage is captured by 

coding the appropriate Smart Flag condition state. The Smart Flag quantities are 

measured as each, with only one each of any given Smart Flag per bridge. 

For damage due to fatigue, the “Steel Fatigue” Smart Flag, Element No. 356, can 

be used and one of the three condition states assigned. For rust, the “Pack Rust” 

Smart Flag, Element No. 357, can be used and one of the four condition states 

assigned. For damage due to traffic impact, the “Traffic Impact” Smart Flag, 

Element No. 362, can be used and one of the three condition states assigned. For 

cables with section loss, the “Section Loss” Smart Flag, Element No. 363, can be 

used and one of the four condition states assigned. 

See Topics 7.3, 7.11 and 8.3 for the evaluation of girders, floorbeams and 

stringers. 

See Topics 10.1 – 10.2 for the evaluation of abutments, piers and bents. 
12.2-i

Table of Contents

Section 12 ..................................................................................................................................................

Special Bridges 

 12.2 Movable Bridges ................................................................................ 12.2.1 

 

 12.2.1 Introduction.......................................................................... 12.2.1 

 

 12.2.2 Swing Bridges Design Characteristics................................. 12.2.3 

 Center-bearing............................................................... 12.2.4 

 Rim-bearing................................................................... 12.2.5 

 

 12.2.3 Bascule Bridges Design Characteristics .............................. 12.2.6 

 Rolling Lift (Scherzer) Bridge ...................................... 12.2.7 

 Simple Trunnion (Chicago) Bridge............................... 12.2.8 

 Multi-Trunnion (Strauss Bridge)................................. 12.2.10 

 

 12.2.4 Vertical Lift Bridges Design Characteristics .................... 12.2.12 

 Power and Drive System on Lift Span........................ 12.2.12 

 Power and Drive System on Towers........................... 12.2.13 

 

 12.2.5 Special Elements Common to All Movable Bridges ......... 12.2.14 

 Open Gearing .............................................................. 12.2.14 

 Speed Reducers Including Differentials...................... 12.2.15 

 Shafts and Couplings................................................... 12.2.15 

 Bearings....................................................................... 12.2.16 

 Brakes.......................................................................... 12.2.16 

 Drives .......................................................................... 12.2.18 

 Air Buffers and Shock Absorbers ............................... 12.2.19 

 Span Locks.................................................................. 12.2.21 

 Counterweights ........................................................... 12.2.21 

 Live Load Shoes and Strike Plates.............................. 12.2.22 

 Traffic Barriers............................................................ 12.2.23 

 

 12.2.6 Swing Bridge Special Elements......................................... 12.2.24 

 Pivot Bearings ............................................................. 12.2.24 

 Balance Wheels........................................................... 12.2.25 

 Rim-Bearing Rollers ................................................... 12.2.25 

 Wedges........................................................................ 12.2.26 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2-ii

 End Latches................................................................. 12.2.27 

 12.2.7 Bascule Bridge Special Elements ...................................... 12.2.28 

 Rolling Lift Tread and Track Castings........................ 12.2.28 

 Racks and Pinions ....................................................... 12.2.29 

 Trunnions and Trunnion Bearings............................... 12.2.31 

 Hopkins Frame............................................................ 12.2.32 

 Tail (Rear) Locks ........................................................ 12.2.32 

 Center Locks ............................................................... 12.2.33 

 Transverse Locks ........................................................ 12.2.34 

 12.2.8 Vertical Lift Bridge Special Elements............................... 12.2.35 

 Wire Ropes and Sockets.............................................. 12.2.35 

 Drums, Pulleys, and Sheaves ...................................... 12.2.36 

 Span and Counterweight Guides................................. 12.2.36 

 Balance Chains............................................................ 12.2.36 

 Span Leveling Devices................................................ 12.2.36 

 12.2.9 Overview of Common Defects .......................................... 12.2.37 

 Steel............................................................................. 12.2.37 

 Concrete ...................................................................... 12.2.37 

 12.2.10 Inspection Locations and Procedures – Safety .................. 12.2.37 

 Movable Bridge Inspector Safety................................ 12.2.37 

 Inspection Considerations ........................................... 12.2.38 

 Public Safety ............................................................... 12.2.38 

 Navigational Safety..................................................... 12.2.39 

 Structure Safety........................................................... 12.2.41 

 Dependable Operation................................................. 12.2.41 

 12.2.11 Inspection Locations and Procedures of Movable Bridge 

Opening and Closing Sequences........................................... 12.2.41 

 Interlocking for Normal Operation ............................. 12.2.41 

 Opening Sequence....................................................... 12.2.41 

 Closing Sequence........................................................ 12.2.41 

 12.2.12 Inspection Locations and Procedures for Control House .. 12.2.43 

 12.2.13 Inspection Locations and Procedures for Structural 

Members ............................................................................ 12.2.44 

 Defects, Damage and Deterioration ............................ 12.2.44 

 Fatigue......................................................................... 12.2.44 

 Counterweights and Attachments................................ 12.2.44 

 Piers............................................................................. 12.2.46 

 Steel Grid Decks ......................................................... 12.2.47 

 Concrete Decks ........................................................... 12.2.47 

 Other Structural Considerations.................................. 12.2.47 

 12.2.14 Inspection Locations and Procedures for Machinery 

Members ............................................................................ 12.2.48 

 Trial Openings............................................................. 12.2.48 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2-iii

 Machinery Inspection Considerations......................... 12.2.48 

 Operation and General System Condition................... 12.2.48 

 Maintenance Procedures ............................................. 12.2.48 

 Open Gearing .............................................................. 12.2.48 

 Speed Reducers Including Differentials...................... 12.2.49 

 Shafts and Couplings................................................... 12.2.50 

 Bearings....................................................................... 12.2.51 

 Brakes.......................................................................... 12.2.51 

 Drives - Electrical Motors........................................... 12.2.52 

 Drives - Hydraulic Equipment .................................... 12.2.52 

 Auxiliary Drives.......................................................... 12.2.52 

 Drives - Internal Combustion Engines........................ 12.2.52 

 Locks........................................................................... 12.2.52 

 Live Load Shoes and Strike Plates.............................. 12.2.53 

 Air Buffer Cylinders and Shock Absorbers ................ 12.2.53 

 Machinery Frames, Supports, and Foundations.......... 12.2.53 

 Fasteners...................................................................... 12.2.53 

 Wedges........................................................................ 12.2.53 

 Special Machinery for Swing Bridges ........................ 12.2.53 

 Special Machinery for Bascule Bridges...................... 12.2.54 

 Special Machinery for Vertical Lift Bridges............... 12.2.54 

 12.2.15 Electrical Inspection Considerations ................................. 12.2.54 

 Power Supplies............................................................ 12.2.54 

 Motors ......................................................................... 12.2.55 

 Transformers ............................................................... 12.2.55 

 Circuit Breakers .......................................................... 12.2.55 

 Wires and Cables......................................................... 12.2.55 

 Cabinets....................................................................... 12.2.56 

 Conduit........................................................................ 12.2.56 

 Junction Boxes ............................................................ 12.2.57 

 Meters.......................................................................... 12.2.57 

 Control Starters and Contactors/Relays ...................... 12.2.57 

 Limit Switches ............................................................ 12.2.57 

 Selsyn Transmitters and Receivers ............................. 12.2.57 

 Service Light and Outlet ............................................. 12.2.57 

 12.2.16 Hydraulic Inspection Considerations................................. 12.2.58 

 

 12.2.17 Recordkeeping and Documentation................................... 12.2.59 

 General ........................................................................ 12.2.59 

 Inspection and Maintenance Data ............................... 12.2.60 

 12.2.18 Evaluation.......................................................................... 12.2.67 

 NBI Rating Guidelines................................................ 12.2.67 

 Element Level Condition State Assessment................ 12.2.67 

 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2-iv

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12.2.1 

Topic 12.2 Movable Bridges 

12.2.1 

Introduction This topic serves as an introduction to the highly specialized area of movable 

bridge inspection (see Figure 12.2.1). It focuses on the types of movable bridges 

and special elements associated with the various bridge types. 

Figure 12.2.1 Movable Bridge 

Movable bridges are normally constructed only when fixed bridges are either too 

expensive or impractical. Movable bridges are constructed across designated 

“Navigable Waters of the United States”, in accordance with “Permit Drawings”

approved by the U.S. Coast Guard. When a movable bridge is fully open, it must 

provide the channel width and the underclearance shown on the Permit Drawings 

(see Figure 12.2.2). If the bridge cannot be opened to provide these clearances, the 

U.S. Coast Guard should be notified immediately and action taken to restore the 

clearances. If that is impossible, application must be made to revise the Permit 

Drawings. 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.2 

Figure 12.2.2 Typical “Permit Drawing” Showing Channel Width and 

Underclearance in Closed and Open Position 

If any work is to be done in the channel or on the movable span to reduce the 

clearances from those shown on the Permit Drawing, an additional permit, 

covering the scheduled time for the work, must be obtained from the U.S. Coast 

Guard District. 

The U.S. Coast Guard publishes Local Notices to Mariners to keep waterway users 

informed of work in progress that may affect navigation. The permittee must keep 

the U.S. Coast Guard informed of all stages of construction. 

An inspection of the bridge should verify that the bridge conforms to the Permit 

Drawing and that the operator is instructed to open the bridge to the fully open 

position every time the bridge is operated. Failure to do this would establish a 

precedent that a vessel is expected to proceed before the green navigation lights 

have turned “on”. Any accident caused as a result of this practice could be ruled 

the fault of the bridge owner. 

Early America's engineering literature did not establish where the first iron 

drawbridge was built. The first all-iron movable bridge in the Midwest was 

completed in 1859 carrying Rush Street over the Chicago River (see Figure 

12.2.3). The bridge was a rim bearing swing span and was probably operated by 

steam. It was destroyed November 3, 1863 when it was opened while a drove of 

cattle was on one end. It was rebuilt but destroyed by the great Chicago fire of 

1871. 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.3 

Figure 12.2.3 The First All-Iron Movable Bridge in the Midwest was Completed 

in 1859 (Photo on File at the Chicago Historical Society) 

All categories of movable bridges are powered by electric-mechanical or 

hydraulic-mechanical drives with power driven pinions operating against racks, or 

by hydraulic cylinders. A small number are hand powered for normal operation. A 

few bridges use hand power for standby operation. Three categories of movable 

bridges comprise over 95 percent of the total number of movable bridges within 

the United States. These categories are: 

3⁄4 Swing bridges 

3⁄4 Bascule bridges 

3⁄4 Vertical lift bridges 

12.2.2 

Swing Bridges 

Design 

Characteristics 

Swing bridges consist of two-span trusses or continuous girders, which rotate 

horizontally about the center (pivot) pier (see Figure 12.2.4). The spans are 

usually, but not necessarily, equal. When open, the swing spans are cantilevered 

from the pivot (center) pier and must be balanced longitudinally and transversely 

about the center. When closed, the spans are supported at the pivot pier and at two 

rest (outer) piers or abutments. In the closed condition, wedges are usually driven 

under the outer ends of the bridge to lift them, thereby providing a positive 

reaction sufficient to offset any possible negative reaction from live load and 

impact in the other span. This design feature prevents uplift and hammering of the 

bridge ends under live load conditions. 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.4 

Figure 12.2.4 Center-Bearing Swing Bridge 

Swing spans are subdivided into two types: 

3⁄4 Center-bearing 

3⁄4 Rim-bearing

Center-Bearing Center-bearing swing spans carry the entire load of the bridge on a central pivot 

(usually metal discs). Balance wheels are placed on a circular track around the 

outer edges of the pivot pier to prevent tipping (see Figures 12.2.5 and 12.2.6). 

When the span is closed, wedges similar to those at the rest piers are driven under 

each truss or girder at the center pier. This relieves the center bearing from 

carrying any live load. However, these wedges should not raise the span at the 

pivot pier, but should merely be driven tight. 

The latest swing spans built are nearly all of the center-bearing design. Centerbearing swing spans are less complex and less expensive to build than rim-bearing 

swing spans. 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.5 

Figure 12.2.5 Center-Bearing Swing Span in Closed Position 

Figure 12.2.6 Layout of Center-Bearing Type Swing Span with Machinery on 

the Span 

Rim-Bearing Rim-bearing swing spans transmit all loads, both dead and live, to the pivot pier 

through a circular girder or drum to beveled rollers. The rollers move on a circular 

track situated inside the periphery of the pier. The rollers are aligned and spaced 

on the track by concentric spacer rings. This type of swing span bridge also has a 

central pivot bearing which carries part of the load. This pivot bearing is 

connected to the rollers by radial roller shafts and keeps the span centered on the 

circular track. 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.6 

On both types of swing bridges, the motive power is usually supplied by electric 

motor(s), hydraulic motor(s), or hydraulic cylinder(s), although gasoline engines 

or manual power may also be used. The bridge is rotated horizontally by a circular 

rack and pinion arrangement, or cylinders. 

12.2.3 

Bascule Bridges 

Design 

Characteristics 

Bascule bridges open by rotating a leaf or leaves (movable portion of the span) 

from the normal horizontal position to a point that is nearly vertical, providing an 

open channel of unlimited height for marine traffic (see Figure 12.2.7).

Figure 12.2.7 Bascule Bridge in the Open Position 

If the channel is narrow, a single span may be sufficient. This is called a singleleaf bascule bridge. For wider channels, two leaves are used, one on each side of 

the channel. When the leaves are in the lowered position, they meet at the center 

of the channel. This is known as a double-leaf bascule bridge. 

A counterweight is necessary to hold the raised leaf in position. In older bridges, 

the counterweight is usually overhead, while in more modern bascule bridges, the 

counterweight is placed below the deck and lowers into a pit as the bridge is 

opened. 

The leaf lifts up by rotating vertically about a horizontal axis. The weight of the 

counterweight is adjusted by removing or adding balance blocks in pockets to 

position the center of gravity of the moving leaf at the center of rotation. When 

the bridge is closed, a forward bearing support located in front of the axis is 

engaged and takes the live load reaction. On double-leaf bascule bridges, a taillock behind the axis and a shear lock at the junction of the two leaves are also 

engaged to stiffen the deck. 

There are many types of bascule bridges, but the most common are the following 

three types: 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.7 

3⁄4 Rolling lift (Scherzer) bridge 

3⁄4 Simple trunnion (Chicago) bridge 

3⁄4 Multi-trunnion (Strauss) bridge 

Rolling Lift (Scherzer) 

Bridge 

The first rolling lift bridge was completed in 1895 in Chicago, and was designed 

by William Scherzer. The entire moving leaf, including the front arm with the 

roadway over the channel and the rear arm with the counterweight, rolls away 

from the channel while the moving leaf rotates open (see Figures 12.2.8 and 

12.2.9). On this type of bridge, curved tracks are attached to each side of the tail 

end of the leaf. The curved tracks roll on flat, horizontal tracks mounted on the 

pier. Square or oblong holes are machined into the curved tracks. The horizontal 

tracks have lugs (or teeth) to mesh with the holes preventing slippage as the leaf 

rolls back on circular castings whose centerline of roll is also the center of gravity 

of the moving leaf. 

Figure 12.2.8 Rolling Lift Bascule Bridge Schematic 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.8 

Figure 12.2.9 Double-Leaf Rolling Lift Bascule 

The simple principal of this type of bridge can be seen easiest with a railroad 

bridge. The dead load of the bridge is balanced about the centerline of the drive 

pinion (center of roll). The pinion teeth are engaged with the teeth on the rack 

casting. When the pinion turns it moves along on the fixed rack and causes the 

span to rotate on the circular tread casting as it rolls back on the track casting. 

The weight of the leaf, including the superstructure and counterweight, is 

supported by the curved tracks resting on the horizontal tracks. The counterweight 

is positioned to balance the weight of the leaf. 

On one variation of this type, the trusses on the two leaves acted as three-hinged

arches when closed. There is a 94.5 m (310 feet) span between the centerline of 

bearings. This bridge was built across the Tennessee River at Chattanooga in 1915, 

and it is believed to be the third longest double-leaf bascule in the world. It 

provides an 89.9 m (295-foot) channel, which is the widest channel spanned by a 

bascule bridge. 

Simple Trunnion 

(Chicago) Bridge 

The Chicago Bridge Department staff of Engineers built the first Chicago type 

simple trunnion bascule bridge in 1902. This type of bascule bridge consists of a 

forward cantilever arm out over the channel and a rear counterweight arm (see 

Figure 12.2.10). The leaf rotates about the trunnions. Each trunnion is supported 

on two bearings, which in turn, are supported on the fixed portion of the bridge 

such as trunnion cross-girder, steel columns, or on the pier itself (see Figures 

12.2.11, 12.2.12 and 12.2.13). Forward bearing supports located in front of the 

trunnions are engaged when the leaf reaches the fully closed position. They are 

intended to support only live load reaction. Uplift supports are located behind the 

trunnions to take uplift until the forward supports are in contact (if misadjusted) 

and to take the live load uplift that exceeds the dead load reaction at the trunnions. 

If no forward live load supports are provided or if they are grossly misadjusted, the 

live load and the reaction at the uplift supports are added to the load on the 

trunnions. A double-leaf bascule bridge of this type in Lorain, Ohio has 101.5 m 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.9 

(333 feet) between trunnions. It was built on a skewed crossing of a river, and it is 

believed to be the second longest double-leaf bascule in the world. Of the three 

types of movable bridges, the simple trunnion is by far the most popular. 

Figure 12.2.10 Trunnion Bascule Bridge Schematic 

Figure 12.2.11 Double-Leaf Trunnion Bascule Bridge 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.10 

Figure 12.2.12 Each Trunnion is Supported on Two Bearings 

Figure 12.2.13 Trunnion Bascule Bridge Machinery (One Quarter Shown) is 

Located Outside of the Bascule Trusses on the Pier 

Multi-Trunnion (Strauss 

Bridge) 

The first multi-trunnion (Strauss) bascule bridge was designed by J.B. Strauss and 

completed during 1905 in Cleveland, Ohio. There are many variations of multitrunnion bascule bridges, but basically one trunnion supports the moving span, one 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.11 

trunnion supports the counterweight, and two link pins are used to form the four 

corners of a parallelogram-shaped frame that changes angles as the bridge is 

operated. The counterweight link keeps the counterweight hanging vertically from 

the counterweight trunnions while the moving leaf rotates about the main 

trunnions (see Figure 12.2.14). One variation of this parallelogram layout is the 

heel trunnion. A double-leaf bascule bridge of this type in Sault St. Marie, 

Michigan has 102.4 m (336 feet) between the span trunnions. It was built across 

the approach to a lock in 1914, and it is believed to be the longest double-leaf 

bascule in the world. 

Figure 12.2.14 Multi-Trunnion, Strauss Type Bascule Bridge 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.12 

12.2.4 

Vertical Lift 

Bridges Design 

Characteristics 

Vertical lift movable bridges have a movable span with a fixed tower at each end. 

The span is supported by steel wire ropes at its four corners. The ropes pass over 

sheaves (pulleys) atop the towers and connect to counterweights on the other side. 

The counterweights descend as the span ascends (see Figure 12.2.15). 

Figure 12.2.15 Vertical Lift Bridge Schematic 

There are two basic types of vertical lift bridges: 

3⁄4 Power and drive system on lift span 

3⁄4 Power and drive system on towers 

Power and Drive System 

on Lift Span 

The first vertical lift bridge completed during 1894 in Chicago was designed by 

J.A.L. Waddell. This bridge type locates the power on top of the lift truss span. 

The actual lifting is accomplished using “up-haul and down-haul ropes” where 

turning drums wind the up-haul (lifting) ropes as they simultaneously unwind the 

down-haul ropes. Vertical lift bridge machinery is located on top of the lift truss 

span, and the operating drums rotate to wind the up-haul (lifting) ropes as they 

simultaneously unwind the down-haul ropes (see Figure 12.2.16). A variation of 

this type provides drive pinions at both ends of the lift span which engage racks on 

the towers. 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.13 

Figure 12.2.16 Vertical Lift Bridge Machinery is Located on Top of the Lift 

Truss Span, and the Operating Drums Rotate to Wind the Up-Haul 

(Lifting) Ropes as They Simultaneously Unwind the Down-Haul 

Ropes 

Power and Drive System 

on Towers 

The other basic type of vertical lift bridge locates the power on top of both towers, 

where drive pinions operate against circular racks on the sheaves. The lifting 

speed at both towers must be synchronized to keep the span horizontal as it is 

lifted (see Figures 12.2.17 and 12.2.18). 

Figure 12.2.17 Vertical Lift Bridge Machinery is Located on the Towers, and the 

Rim Gears (and Operating Sheaves) are Rotated to Raise and 

Lower the Bridge 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.14 

Figure 12.2.18 Vertical Lift Bridge with Power and Drive System on Towers 

12.2.5 

Special Elements 

Common to All 

Movable Bridges 

Particular attention should be given to the special elements found in swing bridges, 

bascule bridges, and vertical lift bridges during inspection. These elements are 

commonly found on all types of movable bridges.

Open Gearing Open gearing is used to transmit power from one shaft to another and to alter the 

speed and torque output of the machinery. Beveled gears are also used to change 

direction (see Figure 12.2.19). 

Figure 12.2.19 Open Gearing 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.15 

Speed Reducers 

Including Differentials 

Speed reducers including differentials serve the same function as open gearing (see 

Figure 12.2.20). However, they may contain several gear sets, bearings, and shafts 

to provide a compact packaged unit, which protects its own mechanical elements 

and lubrication system with an enclosed housing. Differential speed reducers also 

function to equalize torque and speed from one side of the mechanical operating 

system to the other.

Figure 12.2.20 Speed Reducer 

Shafts and Couplings Shafts transmit mechanical power from one part of the machinery system to 

another. Couplings transmit power between the ends of shafts in line with one 

another, and several types can be used to compensate for slight imperfections in 

alignment between the shafts (see Figure 12.2.21). 

Figure 12.2.21 Coupling 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.16 

Bearings Bearings provide support and prevent misalignment of rotating shafts, trunnions, 

and pins (see Figure 12.2.22). 

Figure 12.2.22 Bearing 

Brakes Brakes can be of either the shoe type or disc type, and can be released manually, 

electrically, or hydraulically (see Figures 12.2.23 and 12.2.24). They are generally 

spring applied for fail safe operation. Motor brakes are located close to the drive to 

provide dynamic braking capacity, except that some types of drives can provide 

their own braking capability, thereby eliminating the need for separate motor 

brakes. Machinery brakes are located closer to the operating interface between 

movable and fixed parts of the bridge and are used to hold the span statically, in 

addition to serving as emergency brakes in many cases. Supplemental emergency 

brakes are sometimes also provided. 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.17 

Figure 12.2.23 Shoe Type Break 

Figure 12.2.24 Spring Set Hydraulically Released Disc Break
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.18 

Drives Drives can consist of electric motors, hydraulic equipment, or auxiliary drives. 

For electric motors, either AC or DC power may be used. AC power is often used 

to power wound rotor motors with torque controllers on older bridges, while new 

bridges may utilize squirrel cage induction motors with adjustable frequency speed 

control. DC motors can also provide speed control. 

For hydraulic equipment, prime movers may include either large actuating 

cylinders or hydraulic motors (see Figure 12.2.25). Either type of drive must be 

supplied with pressure to provide force and fluid flow to provide speed to the 

operating system. Electrically operated hydraulic power units consisting of a 

reservoir and pump, with controls, provide power to the operating systems. 

For auxiliary drives, emergency generators are provided to serve in the event of 

power failure. Auxiliary motors and hand operators, with their clutches and other 

mechanical power transmission components, are provided to serve in the event the 

main drive fails (see Figure 12.2.26). In some cases, to prevent the need for larger 

auxiliary generators, the auxiliary motors are required for use any time the 

auxiliary generators are used, requiring increased time of operation.

Figure 12.2.25 Low Speed High Torque Hydraulic Motor 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.19 

Figure 12.2.26 AC Emergency Motor 

Air Buffers and Shock 

Absorbers 

Air buffers and shock absorbers are located between the span and the pier at points 

where impact may occur between the two (see Figures 12.2.27 and 12.2.28). A 

cross section of the buffer shows the air chamber and seals on the piston. As the 

span lowers, the rod is pushed in, causing the air inside to be compressed (see 

Figure 12.2.29). A pressure relief valve allows the air to escape beyond the 

pressure setting. Forces are required to build-up and keep the pressure of the air at 

the movement of the span for a “soft” touchdown on the bearings. Shock absorbers 

provide the same purpose as the air buffers. However, they are completely selfcontained and, therefore, require very little maintenance. 

Figure 12.2.27 Air Buffer 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.20 

Figure 12.2.28 Shock Absorber 

Figure 12.2.29 Typical Air Buffer Schematic 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.21 

Span Locks Span lock bars at the end of the span are driven when the span is fully closed to 

prevent movement under live load. Span locks may also be provided at other 

locations on the span to hold the span in an open position against strong winds or 

to prevent movement from an intermediate position. They can be driven either 

mechanically or hydraulically (see Figures 12.2.30 and 12.2.31). 

Figure 12.2.30 Typical Mechanically Operated Span Lock 

Figure 12.2.31 Hydraulic Cylinder that Drives Lock Bars

Counterweights Adjustable quantities of counterweight blocks are provided in addition to the 

permanent counterweight, which is part of the structure so that adjustments may be 

made from time to time due to changes in conditions (see Figures 12.2.32 and 

12.2.33). A movable span is designed to function in a balanced condition, and 

serious unbalanced conditions will cause overstress or even failure of the 

mechanical or structural elements. 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.22 

Figure 12.2.32 Concrete Counterweight on a Single-Leaf Bascule Bridge 

Figure 12.2.33 Concrete Counterweight on a Vertical Lift Bridge 

Live Load Shoes and 

Strike Plates 

Live load shoes and strike plates between the movable and fixed portions of the 

bridge are designed to bear most or all of the live load when the bridge is carrying 

traffic (see Figure 12.2.34). 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.23 

Figure 12.2.34 Closed Span Resting on Live Load Shoes 

Traffic Barriers Traffic barriers are heavy-duty movable gates or posts that are designed to prevent 

a vehicle from plunging from the roadway into the draw or into the pit below the 

bridge (see Figure 12.2.35. Their operation is important for public safety. They 

are used mainly in situations where a large opening exists between the approach 

span and the movable span when it is open. 

Figure 12.2.35 Traffic Barrier 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.24 

12.2.6 

Swing Bridge 

Special Elements 

Swing bridges are designed utilizing the following special elements.

Pivot Bearings In center-bearing types (with balance wheels), the axially loaded thrust bearing is 

usually composed of spherical discs, attached to top and bottom bases, enclosed in 

an oil box to provide lubrication and prevent contamination (see Figure 12.2.36). 

In rim-bearing types, the pivot bearing is also enclosed but will be radial loaded, 

maintaining the position of the pivot shaft or king pin. 

Figure 12.2.36 Center Pivot Bearing 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.25 

Balance Wheels On center-bearing types only, non-tapered balance wheels bear on the circular rail 

concentric to the pivot bearing only when the span is subjected to unbalanced 

loading conditions (see Figure 12.2.37). At other times, when the span is not 

subjected to unbalanced loads, a gap should be found between each wheel and the 

rail. 

Figure 12.2.37 Balance Wheel in-place over Circular Rack 

Rim-Bearing Rollers Usually tapered to allow for the differential rolling distance between the inside and 

outside circumferences of the rail circle, rim-bearing rollers should bear at all 

times. 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.26 

Wedges End wedges are used to raise the ends of the span and support live load under 

traffic (see Figure 12.2.38). The end wedge bearings are under all four corners of 

the span. Center wedges are used to stabilize the center of the span and to prevent 

the center bearing from supporting live load. Wedges may be actuated by 

machinery and linkage, which connects wedges to actuate together or each wedge 

may have its own actuator (see Figure 12.2.39). 

Figure 12.2.38 End Wedge 

Figure 12.2.39 Hydraulic Cylinder Actuator
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.27 

End Latches Located at the center of one or both rest piers, end latches generally consist of a 

guided tongue with roller mounted on the movable span that occupies a pocket 

mounted on the rest pier when the span is in the closed position. To open the span, 

the tongue is lifted until it clears the pocket at the time the wedges are withdrawn 

(see Figure 12.2.40). As the span is swung open, the latch tongue is allowed to 

lower or fall into a position in which the roller may follow along a rail or track 

mounted on the pier. When closing, the tongue rolls along the rail or track and up 

a ramp which leads to the end latch pocket where the tongue is allowed to drop to 

center the span. 

Figure 12.2.40 End Wedges Withdrawn and End Latch Lifted 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.28 

12.2.7 

Bascule Bridge 

Special Elements 

Bascule bridges utilize the following elements specific to their design.

Rolling Lift Tread and 

Track Castings 

Rolling lift tread and track castings are rolling surfaces which support the bascule 

leaves as they roll open or closed (see Figure 12.2.41). Tread sockets and track 

teeth prevent transverse and lateral movement of the span due to unbalanced 

conditions, such as wind, during operation and especially when held in the open 

position. 

Figure 12.2.41 Circular Lift Tread and Track Castings 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.29 

Racks and Pinions In the rolling lift rack and pinion, the driving pinion engages the rack teeth at the 

centerline of the roll (see Figure 12.2.42). 

In the trunnion rack and pinion, the circular rack castings are attached in the plane 

of the truss (or girder) in front of the counterweight (see Figures 12.2.43 and 

12.2.44). 

The drive pinions are overhung in order to engage the rack teeth. A cover is 

placed over the pinions for safety and to keep debris from falling on it. 

Figure 12.2.42 Rack Casting and Pinion
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.30 

Figure 12.2.43 Rack Casting Ready for Fabrication 

Figure 12.2.44 Drive Pinion 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.31 

Trunnions and Trunnion 

Bearings 

Trunnions and trunnion bearings (see Figure 12.2.45) are large pivot pins or shafts. 

Their bearings support the leaf as it rotates during operation as well as supporting 

dead load when the bridge is closed. Some designs require the trunnions to carry 

live load in addition to dead load (see Figure 12.2.46). 

Figure 12.2.45 Trunnion Bearing 

Figure 12.2.46 Trunnion Design Drawing
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.32 

Hopkins Frame A Hopkins frame machinery arrangement is provided on some trunnion bascule 

bridges. The main drive pinion locations are established in relationship to their 

circular racks by a pivot point on the pier and pinned links attached to the 

trunnions. 

Tail (Rear) Locks Located at the rear of the bascule girder on the pier, tail locks prevent inadvertent 

opening of the span under traffic or under a counterweight-heavy condition should 

the brakes fail or be released (see Figure 12.2.47). 

Figure 12.2.47 Rear Lock Assembly 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.33 

Center Locks Center locks are provided to transfer shear load from one leaf to the other when the 

bridge is under traffic. Center locks may consist of a driven bar or jaw from one 

leaf engaging a socket on the other leaf, or may be a meshing fixed jaw and 

diaphragm arrangement with no moving parts (see Figure 12.2.48). Without the 

center lock engaged, a double-leaf bascule functions as a cantilevered span, 

experiencing four times the negative bending moment, with proportional increases 

in stresses, at the pier. 

Figure 12.2.48 Center Lock Jaws 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.34 

Transverse Locks In twin bascule bridges that are split longitudinally to allow flexibility during 

construction, repair, or rehabilitation, transverse locks between the inside girders 

are used to keep the pairs together during operation (see Figure 12.2.49). These are 

usually operated manually, as they are not normally used for long periods of time. 

Figure 12.2.49 Transverse Locks on Underside can be Disengaged 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.35 

12.2.8 

Vertical Lift Bridge 

Special Elements 

Vertical lift bridges may utilize the following elements peculiar to their design.

Wire Ropes and Sockets Wire ropes and sockets include up-haul and down-haul operating ropes and 

counterweight ropes (see Figures 12.2.50 and 12.2.51). Ropes consist of individual 

wires twisted into several strands that are wound about a steel core. Fittings secure 

the ends of the rope and allow adjustments to be made. 

Figure 12.2.50 Wire Rope Figure 12.2.51 Wire Rope Sockets and 

Fittings
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.36 

Drums, Pulleys, and 

Sheaves 

Drums are used to wind a rope several times around to extend or retract portions of 

the bridge (see Figure 12.2.52). Pulleys and sheaves change the direction of the 

rope or guide it at intermediate points between ends of the rope. 

Figure 12.2.52 Drums Wind Up the Up-Haul (Lifting) Ropes as they 

Simultaneously Unwind the Down-Haul Ropes

Span and Counterweight 

Guides 

Span and counterweight guides are located between tower and span or 

counterweight to prevent misalignment. 

Balance Chains Balance chains are provided to compensate for the weight of counterweight rope 

that travels from the span side to the counterweight side of the sheaves at the top 

of the tower as the span is raised. Weight of chain is removed from the 

counterweight and is supported by the tower as rope weight is increased on the

counterweight side of the sheaves on the tower. 

Span Leveling Devices Mechanical or electrical, span leveling devices compensate and adjust the 

movement of the two ends of the span during operation to prevent unsynchronized 

movement. 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.37 

12.2.9 

Overview of 

Common Defects 

Steel Common defects that can occur to steel members of movable bridges include: 

3⁄4 Paint failures 

3⁄4 Corrosion 

3⁄4 Fatigue cracking 

3⁄4 Collision damage 

3⁄4 Overloads 

3⁄4 Heat damage 

See to Topic 2.3 for a detailed presentation of the properties of steel, types and 

causes of steel deterioration, and the examination of steel. Refer to Topic 8.1 for 

Fatigue and Fracture in Steel Bridges. 

Concrete Common defects that occur to concrete members of movable bridges include: 

3⁄4 Cracking (flexure, shear, temperature, shrinkage, mass concrete) 

3⁄4 Scaling 

3⁄4 Delamination 

3⁄4 Spalling 

3⁄4 Chloride contamination 

3⁄4 Efflorescence 

3⁄4 Ettringite formation 

3⁄4 Honeycombs 

3⁄4 Pop-outs 

3⁄4 Wear 

3⁄4 Collision damage 

3⁄4 Abrasion 

3⁄4 Overload damage 

3⁄4 Reinforcing steel corrosion 

Refer to Topic 2.2 for a detailed explanation of the properties of concrete, types 

and causes of concrete deterioration, and the examination of concrete. 

12.2.10 

Inspection 

Locations and 

Procedures - Safety 

Movable Bridge 

Inspector Safety 

It is imperative that all movable bridge inspectors coordinate their work with the 

Bridge Operator and emphasize the need for advance warning of a bridge opening. 

The Bridge Operator should not operate the bridge until being notified by all 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.38 

inspectors that they are ready for an opening. There are many ways that this can be 

accomplished, such as placing a warning note on the control console or opening 

the circuit breakers and locking the compartment to the equipment that they will be 

inspecting. 

Inspection 

Considerations 

Important considerations for a movable bridge inspector include observing and 

making comments in the inspection report on the following safety considerations. 

Public Safety Public safety considerations include good visibility of roadway and sidewalk for 

the Bridge Operator (see Figure 12.2.53). Adequate time delay on traffic signals 

for driver reaction and before lowering gates. Interlock, all “gates down” before 

raising bridge (bypass available if traffic signals are on). Interlock, bridge must be 

closed before gates can be raised (bypass available if locks are driven). Interlock, 

traffic signals do not turn off until all gates are fully raised (bypass available). 

Observe the location of the bridge opening in relation to the gates, traffic lights 

and bells, and determine whether approaching motorists can easily see them. 

Check their operation and physical condition to determine if they are functioning 

and well maintained. Recommend replacement when conditions warrant it. 

Unprotected approaches, such as both ends of a swing bridge and vertical lift 

bridge and the open end of a single-leaf bascule bridge, should preferably have 

positive resistance barriers across the roadway, with flashing red lights as provided 

on the gate arms (see Figure 12.2.54). High-speed roadways and curved

approaches to a movable bridge should preferably have advanced warning lights 

(flashing yellow). 

Figure 12.2.53 Operator’s House with Clear View of Traffic Signals and Lane 

Gates 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.39 

Figure 12.2.54 Traffic Control Gate

Navigational Safety Navigational safety considerations include compliance with minimum channel 

width with any restriction on vertical clearance when span is open for navigation. 

Minimum underclearance designated on the permit drawing should be provided. 

Underclearance gauges for closed bridges must be inspected for accuracy, 

visibility, and legibility.

All navigation lights should have a relay for backup light, and red span lights 

should not change to green until both leaves are fully open (see Figure 12.2.55).

Navigation lights are very important and should be checked for broken lenses, 

deteriorated insulation of wiring and cable, and dry and clean interior. 

Marine radio communication should be functional (see Figure 12.2.56). Operator 

should be able to automatically sound the emergency signal to navigation vessels 

if bridge cannot be opened. 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.40 

Figure 12.2.55 Navigational Light 

Figure 12.2.56 Marine Two-Way Radio Console
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.41 

Structure Safety Structure safety considerations include the structural ability to carry the anticipated 

loads. There must be pressure relief valves on hydraulic power units to limit 

hydraulic forces applied to machinery and structure. Horsepower applied to 

machinery and structure must be kept within design limits by limiting speed. 

Dependable Operation The movable bridge should be operated in the normal and emergency modes to 

check all interrelated interlocks and to verify every component is operating 

correctly. 

12.2.11 

Inspection 

Locations and 

Procedures of 

Movable Bridge 

Opening and 

Closing Sequences 

These bridges are considered to be complex according to the NBIS regulations. 

The NBIS requires identification of specialized inspection procedures, and 

additional inspector training and experience required to inspect these complex 

bridges. The bridges are then to be inspected according to these procedures. 

Interlocking for Normal 

Operation 

During normal operation, the inspector should verify that each interlock functions 

properly and can be bypassed (when provided). The controls for the traffic signals, 

traffic gates, center or rear locks, emergency brakes, and the bridge operation 

should be so interlocked that they can only be operated in the following sequences.

Opening Sequence The bridge opening sequence should be as follows: 

1. Activate traffic signals. 

2. Lower oncoming gates and, when traffic has cleared, lower off-going 

gates. “All gates down” interlocked for withdrawing locks (bypass 

provided). 

3. Press "raise" button if automatic operation is provided or, if manual 

operation is provided, proceed as follows: 

a. Withdraw locks – “Locks Withdrawn.” Interlocked for bridge 

operation (no bypass). 

b. Release emergency brakes - no interlock provided. Warning 

buzzer sounds if brakes are not released when power is applied to 

motors to move bridge. 

c. Accelerate leaves to full speed. 

d. When advanced to nearly open position, decelerate leaves to slow 

speed and stop at nearly open position. 

e. At nearly open position, with reduced power, lower leaves to stop 

at fully open position. 

f. Set emergency brakes. 

Closing Sequence The bridge closing sequence should be as follows: 

1. Press “lower” button if automatic operation is provided or, if manual 

operation is provided, proceed as follows: 

a. Release emergency brakes. 

b. Accelerate leaves to full speed. 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.42 

c. For all types of bridges with lock bars: 

(1) At advanced nearly closed position, decelerate leaves to 

slow speed. Leaves should stop at nearly closed position 

by action of the bridge limit switch. 

(2) At nearly closed position with reduced power, lower 

leaves to stop at fully closed position. 

(3) With machinery wound up (bascule bridges and 

counterweight heavy vertical lift bridges) or when span is 

fully closed (swing bridges and span heavy vertical lift 

bridges), set the brakes and drive lock bars. 

d. For rolling lift bridges having jaw and diagram shear locks with 

no moving parts: 

(1) At advanced nearly closed position, decelerate to slow 

speed. The jaw leaf should stop at the “locking position”

(within the “window” to receive the diaphragms) by 

action of the bridge limit switch. 

(2) At advance nearly closed position, decelerate to slow 

speed. The diaphragm leaf should stop in the “clear 

position” (where the lower jaw will clear the diaphragm) 

by action of the bridge limit switch. 

(3) Foot switch must be depressed to provide reduced power 

from this point until both leaves are closed. 

(4) Lower the diaphragm leaf to make “soft” contact with 

lower jaw. 

(5) Close both leaves together with diaphragm castings 

against lower jaws. 

(6) When leaves are fully closed, drive the rear locks. “Fully 

closed” interlock provided for rear lock operation (no 

bypass). 

(7) Set emergency brakes with reduced power applied to 

motors to hold machinery wound up. 

2. Deactivate automatic traffic control, or manually raise gates: 

a. All gates raise, off-going gates should start up before oncoming 

gates raise. 

b. Warning signals and red lights should not turn off until all gates 

are raised, even if the power switch is turned “off” (bypass should 

be provided), after which the green traffic lights are turned “on”. 

Bypass Note: All bypass switches should have handles that are 

spring returned to “off”. When the switch is turned to bypass 

momentarily, a holding relay should hold the bypass activated 

until power is removed from the controls or the switch is turned to 

cancel bypass. These circuits should be provided in order to 

prevent inadvertent use of any bypass. Until a malfunction is 

corrected, the operator must therefore initiate the use of any 

bypass switch that is needed every time the bridge is operated. 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.43 

12.2.12 

Inspection 

Locations and 

Procedures for the 

Control House 

Inspection of the control house is necessary to assure the safety of a movable 

bridge. The operator is responsible for public and navigational safety during 

operation and, together with maintenance personnel, should be most familiar with 

any known structural or operational defects. Operational and maintenance log 

books should be kept in the control house for reference. The resources within the 

control house can therefore provide a great deal of general information, through 

the knowledge of its personnel and the records stored there. The position of the 

control house should provide the best general view of the bridge itself. 

Consult with the bridge operators to ascertain whether there are any changes from 

the normal operation of the bridge. Note whether all Coast Guard, Corps of 

Engineers, and local instructional bulletins are posted. Check for obvious 

hazardous operating conditions involving the safety of the operator and 

maintenance personnel. 

Note where the control panel is located in relation to roadway and waterway, and 

also whether the bridge operator has a good view of approaching boats, vehicles, 

and pedestrians (see Figure 12.2.57). Check operation of all closed circuit TV 

equipment, and evaluate its position for safe operation. If controls are in more 

than one location, note description of the other locations and include their 

condition as well as the information about the control house. Note whether 

alternate warning devices such as bullhorns, lanterns, flasher lights, or flags are 

available. 

Note whether the structure shows cracks, and determine whether it is windproof 

and insulated. Check for any accumulations of debris, which may be readily 

combustible. Check controllers while bridge is opening and closing. Look for 

excess play and for sparking during operation. Note whether the submarine cables 

are kinked, hooked, or deteriorated, especially at the exposed area above or below 

the water. In tidal areas, check for marine and plant growth. Note if the ends of 

the cable have been protected from moisture. 

Figure 12.2.57 Control Panel 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.44 

12.2.13 

Inspection 

Locations and 

Procedures for 

Structural 

Members 

Defects, Damage, and 

Deterioration 

Defects, damage, and deterioration, typically detrimental to all steel and concrete 

structures, must be noted during the inspection of all types of movable bridges. 

Most of the bridge structure defects and deterioration listed in Section 2: Materials,

as potential problems apply to movable spans also. 

Fatigue Fatigue can be a problem with movable bridges due to the reversal or the 

fluctuation of stresses as the spans open and close (see Figure 12.2.58). Any 

member or connection subject to such stress variations should be carefully 

inspected for signs of fatigue. 

Figure 12.2.58 Stress Reversals in Members 

Counterweights and 

Attachments 

Inspect the counterweights to determine if they are sound and are properly affixed 

to the structure. Also check temporary supports for the counterweights that are to 

be used during bridge repair and determine their availability should such an 

occasion arise. Determine whether the counterweight pockets are properly 

drained. On vertical lift bridges, be sure that the sheaves and their supports are 

well drained. Examine every portion of the bridge where water can collect. All 

pockets that are exposed to rain and snow should have a removable cover. Check 

for debris, birds, animals, and insect nests in the counterweight pockets. 

Where steel members pass through or are embedded in the concrete check for any 

corrosion of the steel member and for rust stains on the concrete. Look for cracks 

and spalls in the concrete. 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.45 

Where lift span counterweight ropes are balanced by chains (or other means), 

make sure the links hang freely, and check these devices along with slides, 

housings, and storage devices for deterioration and for adequacy of lubrication, 

where applicable (see Figure 12.2.59). 

Determine whether the bridge is balanced and whether extra balance blocks are 

available. A variation in the power demands on the motor, according to the span's 

position, is an indication of an unbalanced leaf or span. If the controls provide a 

“drift” position, it should be used to test the balance. Paint must be periodically 

removed from a lift span properly; otherwise, the counterweights will eventually 

be inadequate. 

Figure 12.2.59 Counterweights on Vertical Lift Bridge 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.46 

Piers Take notice of any rocking of the piers when the leaf is lifted. This is an indicator 

of a serious deficiency and should be reported at once. Survey the spans including 

towers to check both horizontal and vertical displacements. This will help to 

identify any foundation movements that have occurred. 

Check the braces, bearings, and all housings for cracks, especially where stress 

risers would tend to occur. Inspect the concrete for cracks in areas where 

machinery bearing plates or braces are attached (see Figure 12.2.60). Note the 

tightness of bolts and the tightness of other fastening devices used. 

Check the pier protection system (see Figure 12.2.61). 

Figure 12.2.60 Concrete Bearing Areas

Figure 12.2.61 Pier Protection Systems – Dolphins and Fenders
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.47 

Steel Grid Decks Structural welds should be sound and the grid decks should have adequate skid 

resistance. Check the roadway surface for evenness of grade and for adequate 

clearance at the joints where the movable span meets the fixed span. For more 

information on steel grid decks, see Topic 5.3. 

Concrete Decks A solid concrete roadway is used over the pier areas (pivot or bascule pier) to keep 

water and debris from falling through onto the piers and mechanical devices. Since 

the machinery room is usually under the concrete deck, check the ceiling for leaks 

or areas that allow debris and rust to fall on the machinery. For more information 

of concrete decks, of movable bridges see Topic 5.2. 

Other Structural 

Considerations 

Other structural considerations include: 

3⁄4 Examine the live load bearings and wedges located under the trusses or 

girders at the pivot pier for proper fit alignment and amount of lift. 

3⁄4 Inspect the fully open bumper blocks and the attaching bolts for cracks in 

the concrete bases. 

3⁄4 Examine the counterweight pit for water. Check the condition of the sump 

pump, the concrete for cracks, and the entire area for debris. 

3⁄4 See if the shear locks are worn. Measure the exterior dimensions of the 

lock bars or diaphragm casting and the interior dimensions of sockets or 

space between jaws to determine the amount of clearance (wear). 

Excessive movement should be reported and investigated further. 

3⁄4 On swing bridges, check the wedges and the outer bearings at the rest 

piers for alignment and amount of lift. This can be recognized by 

excessive vibration of span or uplift when load comes upon the other span.

3⁄4 On double-leafed bascule bridges, measure the differential vertical 

movement at the joint between the two leaves under heavy loads. On other 

types, check for this type of movement at deck joints (breaks in floor) 

between movable and fixed portions of the structure. This can indicate 

excessive wear on lock bars or shear lock members. 

3⁄4 Inspect the joint between the two leaves on double-leaf bascule bridges, or 

the joints between fixed and movable portions of the structure for adequate 

longitudinal clearance for change in temperature (thermal expansion). 

3⁄4 On bascule bridges, see if the front live load bearings fit snugly. Also 

observe the fit of tail locks at rear arm and of supports at outer end of 

single-leaf bridges. 

3⁄4 On rolling lift bascule bridges, check the segmental and track castings and 

their respective supporting track girders (if used) for wear on sides of track 

teeth due to movement of sockets on segmental castings. Compare all 

wear patterns for indications of movement of the leaves. Check for 

cracking at the fillet of the angles forming the flanges of the segmental and 

track girders, cracking in the flanges opposite joints in the castings, and 

cracking of the concrete under the track. Inspect rack support for lateral 

movement when bridge is in motion. 

3⁄4 On multi-trunnion (Strauss) bascule bridges, check the strut connecting the 

counterweight trunnion to the counterweight for fatigue cracks. On several 

bridges, cracking has been noted in the web and lower flanges near the 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.48 

gusset connection at the end nearer the counterweights. The crack would 

be most noticeable when the span is opened. 

12.2.14 

Inspection 

Locations and 

Procedures for 

Machinery 

Members 

Mechanical, electrical, and hydraulic equipment includes specialized areas, which 

are beyond the scope of this manual. Since operating equipment is the heart of the 

movable bridge, it is recommended that expert assistance be obtained when 

conducting an inspection of movable spans. It should be noted that in many cases, 

the owners of these movable bridges follow excellent programs of inspection, 

maintenance, and repair. However, there is always the possibility that some 

important feature may have been overlooked. 

Trial Openings Conduct trial openings as necessary to insure proper operational functioning and 

that the movable span is properly balanced. Trial openings should be specifically 

for inspection. During the trial openings, the safety of the inspection personnel 

should be kept in mind. 

Machinery Inspection 

Considerations 

On all movable structures, the machinery is so important that considerable time 

should be devoted to its inspection. The items covered and termed as machinery 

include all motors, brakes, gears, tracks, shafts, couplings, bearings, locks, 

linkages, over-speed controls, and any other integral part that transmits the 

necessary mechanical power to operate the movable portion of the bridge. 

Machinery should be inspected not only for its current condition, but operational 

and maintenance procedures and characteristics of operation should also be 

analyzed. The items listed below and items similar to them should be inspected 

and analyzed by a machinery or movable bridge specialist. Refer to FHWA-IP-77-

10, Bridge Inspector’s Manual for Movable Bridges and the AASHTO Movable 

Bridge Inspection, Evaluation and Maintenance Manual, for further information 

on inspecting these items. The FHWA-IP-77-10 manual is published by the 

Federal Highway Administration (FHWA), but is currently out of print. 

Operation and General 

System Condition 

Observe the general condition of the machinery as a whole, and its performance 

during operation. Check for smoothness of operation, and note any abnormal 

performance of components. Noise and vibration should also be noted, and the 

source determined. Unsafe or detrimental procedures followed by the operator 

should be noted to prevent injury to the public or to personnel, or damage to the 

equipment. The condition of the paint system should also be noted. 

Maintenance Procedures An evaluation of maintenance procedures in light of design details for the 

equipment should be done. Application methods and frequency of lubrication 

should be checked in the maintenance logbook, if available. General appearance of 

existing applied lubricant should be noted. 

Open Gearing Check open gearing for tooth condition and alignment including over- and underengagement. The pitch lines should match. Excessive or abnormal wear should be 

noted. Inspect the teeth, spokes, and hub for cracks. Observe and note the general 

appearance of the applied lubricants on open gearing. If the lubricant has been 

contaminated, especially with sand or other gritty material, it should be removed 

and new lubricant applied. If there is a way to prevent future contamination, it 

should be recommended in the inspector’s comments in the report. Check the 

teeth of all gears for wear, cleanliness, corrosion, and for proper alignment. 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.49 

Speed Reducers 

Including Differentials 

The exterior of the housing and mountings should be examined for cracks and 

damage (see Figure 12.2.62 and 12.2.63). Check bolts for tightness and note any 

corrosion. The interior of the housing should be inspected for condensation and 

corrosion. Check the condition of gears. Watch for abnormal shaft movement 

during operation, indicating bearing and seal wear. Oil levels and condition of 

lubricant should be checked periodically through the use of sampling and analysis 

techniques. Circulating pumps and lubricating lines should be observed for proper 

operation. Abnormal noise should be noted. 

Figure 12.2.62 Cracked Speed Reducer Housing 

Figure 12.2.63 Leaking Speed Reducer
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.50 

Shafts and Couplings Shafts should be examined for damage, twisting, and strain. Cracks, if suspected, 

may be detected using dye penetrant (see Figure 12.2.64 and Topic 13.3). 

Misalignment with other parts of the machinery system should be noted. Cracks in 

shafts should be measured and the exact location recorded. Consideration should 

be given to replacement of the shaft. Other shafts should be examined in the same 

locations as they were probably made from the same material and fabricated to the 

same details. They have also been exposed to the same magnitude and frequency 

of loading. Coupling hubs, housings, and bolts should be checked for condition. 

Seals and gaskets should be inspected for leaks. Internal inspection of couplings is 

warranted if problems are suspected and can be used to determine tooth wear in 

gear couplings. 

Figure 12.2.64 Hairline Crack Revealed on Shaft from Dye Penetrant Test 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.51 

Bearings Bearing housings, pedestals, and supports should be examined for external 

condition. Any cracks should be noted. Bolts in housings and those used for 

anchors should be checked for tightness, damage, and corrosion. Apparent 

lubrication characteristics should be noted. Grinding noises can be caused by dry 

bearings (unlubricated) (see Figure 12.2.65). In sleeve bearings, the bushings 

should be inspected for damage and excessive wear. Evidence of seal damage in 

anti-friction bearings should be noted. Unusual noise should be investigated. 

Check the trunnion bearings for excessive wear, lateral slip, and loose bolts. 

Figure 12.2.65 Dry Bearing 

Brakes Inspect all braking devices for proper setting of braking torque and for complete 

release of the brakes when actuated. On shoe brakes, check drums and shoes for 

wear, damage, and corrosion, for misalignment of shoes with drums, and for 

clearance when released. Determine if worn linings need replaced. Check for 

proper actuation without leakage by actuators. Linkages and hand releases should 

be free but not sloppy. On enclosed hydraulic disc brakes, make certain there is 

proper actuation without leakage at connections or seals. Check the brakes, limit 

switches, and stops (cylinders and others) for excessive wear and slip movement. 

Note whether the cushion cylinder ram sticks or inserts too easily. The brake limit 

switches should be inspected for proper setting. Observe the surface of the brake 

drum for indications of contact with the brake shoes. Check the pressure 

developed by each disc brake power unit to be sure the brakes are releasing. Also 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.52 

check the manual release on all of the brakes. 

Drives - Electric Motors Check the housing and mountings for damage, corrosion, and fastener condition. 

Inspect bearings for lubrication and note indications of wear (movement) and seal 

leakage at shaft extensions. 

Drives - Hydraulic 

Equipment 

Look for any leakage at connections and seals. Note any corrosion on the cylinder 

rods. Listen to motors and pumps, and note any unusual noise. Power units should 

be checked to make sure all components are functioning and that pressures are 

properly adjusted. Fluid should be sampled periodically and examined for 

contamination and wear metal. Check all main hydraulic power units for charge 

pressure setting and maximum pressure that can be developed by the unit. All 

filters must be checked routinely and replaced as needed. The level of fluid in the 

vertical reservoir should also be checked. 

Auxiliary Drives Check emergency generators for operation and readiness. There should be no oil 

leaks or abnormal noises. Mechanical service specialists and electrical inspectors 

are required for more thorough inspections. Auxiliary motors and hand operators, 

with their clutches and other transmission components, should be checked for 

adjustment and readiness to perform when called upon. 

Drives - Internal 

Combustion Engines 

The detailed inspection of internal combustion engines should be made by 

mechanical engine specialists. Inspection should also include but not be limited to 

the checking of the following conditions: 

3⁄4 If a belt drive is used, look for any wear or slippage. Note the condition of 

all belts and the need for replacement, if any. 

3⁄4 If a friction drive is used, all bracing and bearings should be tight. 

3⁄4 If a liquid coupling is used, make sure that the proper quantity of fluid is 

used. Look for leaks. 

Locks Examine the center locks and tail locks (if used) on double-leafed bascule spans, 

and the end locks on single-leaf bascule bridges, swing bridges, and vertical lift 

bridges. Note whether there is excessive deflection at these joints or vibration on 

the bridge. Inspect the locks for fit and for movement of the span or leaf (or 

leaves). Check lubrication and for loose bolts. The lock housing and its braces 

should have no noticeable movement or misalignment. The paint adjacent to the 

locks will have signs of paint loss or wear if there is movement. Check lock bars, 

movable posts, linkages, sockets, bushings, and supports for damage, cracks, wear, 

and corrosion. 

Check all rear locks in the withdrawn position for clearance from the path of the 

moving leaf as it opens and for full engagement when the leaf is closed. The gap, 

if any, should be measured between the lock plate and the moving leaf bearing 

plate. Check each rear lock hydraulic drive unit for leakage of oil and operation 

for correct length of movement of the lock. 

On bascule bridges, see if the front live load bearings fit snugly. Also observe the 

fit of tail locks at the rear arm and of supports at the outer end of single-leaf 

bridges. 

Actuators should be examined for operational characteristics, including leakage if 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.53 

hydraulic. The quantity and quality of lubricant should be noted. Check for 

alignment, and analyze the type of wear that is occurring. Note condition of 

movable operators. 

Live Load Shoes and 

Strike Plates 

The fasteners and structure should be inspected for defects and corrosion. Contact 

surface conditions should be noted. Check for alignment and movement under 

load. 

Air Buffer Cylinders and 

Shock Absorbers 

Note indications of lack of pressure or stickiness during operation. Check piston 

rod alignment with strike plate. Note the condition of the rod and housing. There 

should be no hydraulic leakage. Check the air filter and function of any pressure 

reading or adjusting devices and the operating pressure, if possible. The air buffers 

should have freedom of movement and development of pressure when closing. 

Inspect the fully open bumper blocks and the attaching bolts for cracks in the 

concrete bases. 

Machinery Frames, 

Supports, and 

Foundations 

There should be no cracking in steel or concrete. Note corrosion and damage. 

Check for deflection and movement under load. The linkages and pin connections 

should have proper adjustment and functional condition. Check motor mounting 

brackets to ensure secure mounting. 

Fasteners Inspect the fasteners for corrosion, loss of section, and tightness. 

Wedges Check the wedges and the outer bearings at the rest piers for alignment and 

amount of lift. This can be recognized by excessive vibration of span or uplift 

when load comes upon the other span. 

Examine the live load bearings and wedges located under the trusses or girders at 

the pivot pier for proper fit alignment and amount of lift. 

Special Machinery for 

Swing Bridges 

Check center bearings for proper and adequate lubrication, oil leaks, and noise. 

Examine the housing for cracking, pitting, fit of joints, and note indications of 

span translation (irregular rotation) at racks and track. Measure for proper 

clearance of balance wheels above track. The tracks and balance wheels should be 

free of wear, pitting, and cracking. Check for proper and adequate lubrication at all 

lubrication points. 

Balance characteristics should be noted as indicated by loads taken by balance 

wheels, and by drag on the rest pier rail. 

Check the rim bearing for wear on tracks and rollers, particularly at rest positions 

where the bridge is carrying traffic. Examine the center pivots and guide rings for 

proper fit, and for wear, pitting, and cracking. Check for proper and adequate 

lubrication at all lubrication points. 

The center (live load) wedges located under the trusses or girders at the pivot pier 

must be examined for proper fit (no lifting) and alignment. Check end wedges and 

bearings at the rest piers for alignment and amount of lift. This can be recognized 

by excessive vibration of the span or uplift when live load crosses the other span. 

The end lift jacks, shoes, and all linkages must be inspected for wear, proper 

bearing under load, and proper adjustment. 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.54 

Note the condition of end latches, including any modification that adversely 

affects their functional design. 

Special Machinery for 

Bascule Bridges 

On rolling lift bascule bridges, check the segmental and track castings and their 

respective supporting track girders (if used) for wear on the sides of track teeth due 

to movement of sockets on segmental castings. The trunnion assemblies must be 

inspected for deflection, buckling, lateral slip, and loose bolts. The trunnions 

themselves should have no corrosion, pitting, or cracking, particularly at stress 

risers. Check the balance of each leaf. Compare all wear patterns for indications 

of movement of the leaves. Check for cracking at the fillet of the angles forming 

the flanges of the segmental and track girders, cracking in the flanges opposite 

joints in the castings, and cracking of the concrete under the track. Inspect rack 

support for lateral movement when bridge is in motion. 

Check trunnion bearings for lubrication of the full width of the bearing. Verify 

that extreme pressure (EP) lubrication oil of the proper grade is used. 

Special Machinery for 

Vertical Lift Bridges 

The condition of wire ropes and sockets, including wire rope lubrication, is 

important. Look for flattening or fraying of the strands and deterioration between 

them. This is reason for replacement. Similarly, check the up-haul and down-haul 

ropes to see if they are winding and unwinding properly on the drums. The need 

for any tension adjustments in up-haul and down-haul ropes should be noted. 

Determine whether ropes have freedom of movement and are running properly in 

sheave grooves. Look for any obstructions to prevent movement of the ropes 

through the pulley system, and check the supports on span drive type bridges. 

Check rope guides for alignment, proper fit, free movement, wear, and structural

integrity of the longitudinal and transverse grooved guide castings. The grooved 

guide castings must be inspected closely for wear in the grooves. The cable holddowns, turnbuckles, cleats, guides, clamps, splay castings, and the travel rollers 

and their guides must be examined. 

Check that balance chains hang freely, that span leveling devices are functioning, 

and that span and counterweight balance closely. Observe if span becomes "out of 

level" during lifting operation. Inspect spring tension, brackets, braces, and 

connectors of power cable reels. 

Check for damage, including cracking, at drums and sheaves. Note the condition 

and alignment of span guides. 

12.2.15 

Electrical 

Inspection 

Considerations 

An electrical specialist should be available for the inspection of the electrical 

equipment. The inspection should be made using FHWA-IP-77-10, Bridge 

Inspector's Manual for Movable Bridges (FHWA-IP-77-10 is currently out of 

print). AASHTO Movable Bridge Inspection, Evaluation and Maintenance Manual, 

may aid in the movable bridge inspection. The inspector should observe the 

functional operation of the bridge and look for abnormal performance of the 

equipment. Check the operational procedures and safety features provided. 

Evaluate the maintenance procedures being followed and check the frequency of 

services performed. 

Power Supplies The normal power supply, standby power supply, and standby generator set (for 

emergency operation of bridge and service lighting) should be examined and the 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.55 

following noted: 

3⁄4 Take megger readings on the cable insulation values, noting the weather 

conditions, namely temperature and humidity. 

3⁄4 Make sure all cable connections are properly tightened. 

3⁄4 Measure the voltage and the current to the motors at regular intervals 

during the operation of the bridge. 

3⁄4 Check the collector rings and windings on the generator set. 

3⁄4 Test starting circuitry for automatic starting and manual starting. 

3⁄4 See if the unit is vibrating while running under load. 

If the power cable has been repaired with a splice, note the condition of the splice 

box seal. 

If no standby power supply has been provided, determine whether a portable 

generator could be used. A manual transfer switch would be a convenient way of 

connecting it. 

Motors Span drive motors, lock motors, brake thrustor motors, and brake solenoids should 

be examined for the same items as given for power supplies. 

Transformers Check dry transformer coil housings, terminals, and insulators, including their 

temperature under load. Observe the frames and supports for rigidity to prevent 

vibration. The liquid filled transformer should be checked in the same way, and the 

oil level should be checked while looking for leakage. Examine oil insulation test 

records. 

Circuit Breakers Check circuit breakers (e.g., air, molded case, and oil) and fuses, including the arc 

chute, contact surfaces, overload trip settings, insulation, and terminal connections. 

Examine oil insulation test records, and observe the closing and tripping operation. 

Record all fuse types and sizes being used. 

Wires and Cables Examine the wiring and cables for both power and control. Note whether the 

submarine cables are kinked, hooked, or deteriorated, especially at the exposed 

area above and below the water. In tidal areas, look for marine and plant growth. 

Note if the ends of the cable have been protected from moisture. Record the 

insulation value of each wire as measured by megger. Look for cracking, 

overheating, and deterioration of the insulation. Check for wear against surfaces 

and especially sharp edges. Check the adequacy of supports and that dirt and 

debris do not accumulate against the conduit and supports. Terminal connections, 

clamps, and securing clips should be checked for tightness, corrosion, and that 

there are wire numbers on the end of each wire. The weight of the wires or cables 

must be carried by the clamps and not by the wire connections at the terminal 

strips. 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.56 

Cabinets Examine the programmable logic controller (PLC) cabinets, control consoles and 

stations, switchboards (see Figure 12.2.66), relay cabinets, motor control centers 

(MCC), and all enclosures for deterioration, debris inside, drainage, operations of 

heater to prevent condensation, and their ability to protect the equipment inside. 

Check the operation of all traffic signals, traffic gates, traffic barriers, and 

navigation lights. Verify that the bridge is open to provide the clearance shown on 

the permit drawing before the green span light turns on. Check the traffic warning 

equipment and control circuits, including the advanced warning signals (if used), 

traffic lights/signals, gates, barriers, and the public address and communication 

equipment. 

Figure 12.2.66 Open Switchboard 

Conduit See if conduit is far enough away from all surfaces to avoid debris from collecting 

against it. Note if it is adequately supported and pitched to drain away from 

junction boxes and pull boxes, so that water is not trapped within. Also, note if all 

conduits have covers with seals. Report deteriorated conduit so that it can be 

replaced with new conduit. The connectors at the ends of all PVC coated conduit 

must be sealed and re-coated after all fittings are installed. 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.57 

Junction Boxes The covers on all junction boxes (JB's) should be examined for an effective seal, 

dry interior, functioning breather-drains, heaters having enough power to prevent 

condensation inside, and terminal strips all secured to the bottom of horizontal JB's 

or to the back of vertical JB's. 

Meters Observe if all voltmeters, ammeters, and watt meters are freely fluctuating with a 

change in load. All switches for meters should be operable. 

Control Starters and 

Contactors/Relays 

Check the operation of this equipment under load, and watch for arcing between 

contacts, snap action of contacts, deterioration of any surfaces, and drainage of any 

moisture. Look for signs of corrosion and overheating. 

Limit Switches All limit switches should be set so they do not operate until they are intended to 

stop the equipment or complete an interlock. The interior should be clean and dry, 

with all springs active. 

Selsyn Transmitters and 

Receivers 

Check for power to the field and signal being sent from the transmitter to the 

receiver. Observe the receiver tracking the rotation of the bridge as it operates. 

Observe the mechanical coupling between the driving shaft and the transmitter, 

checking for damage and misalignment. 

Service Light and Outlet Power should be going to each light and outlet. Note if there is a shield or bar for 

protecting each bulb and socket. It is desirable to have service lights available 

when power is removed from all movable bridge controls and equipment. 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.58 

12.2.16 

Hydraulic 

Inspection 

Considerations 

A hydraulic power specialist should be available for the inspection of the hydraulic

equipment (see Figure 12.2.67). The inspector should observe the functional 

operation of the bridge and look for abnormal performance of the equipment. 

Check the safety features provided and evaluate the maintenance procedures being 

followed, checking the frequency of services performed. Due to the inter-related 

function of components, the requirements for fluid cleanliness, and the need for 

personnel safety, the reservoir and hydraulic lines should not be opened. In 

addition, no components or parts of the power circuit should be shut off or 

adjusted without complete understanding of their function and knowledge of the 

effect such action will have upon the system. Items which should be checked 

during a hydraulic inspection include the following: 

3⁄4 Leakage anywhere in the system should be noted. Significant leakage 

should immediately be brought to the attention of the bridge authority. 

3⁄4 Check for corrosion of reservoir, piping, and connections. 

3⁄4 Sight gauges should be inspected for proper fluid level in reservoir. Note 

gauges with low fluid levels or gauges which cannot be read. 

3⁄4 Unusual noises from any part of the system should be noted. 

3⁄4 Check filter indicators to make sure filters are clean. 

3⁄4 A sample of the hydraulic fluid should be taken for analysis by a testing 

laboratory during periodic inspections. 

Figure 12.2.67 Hydraulic Power Specialists 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.59 

12.2.17 

Recordkeeping and 

Documentation 

General The owner of a movable bridge must keep a complete file available for the 

engineer who is responsible for the operation and maintenance of the bridge. See 

Topic 4.3 for general record keeping and documentation. The file should include 

(if applicable), but not be limited to, the following: 

3⁄4 Copy of the latest approved permit drawing 

3⁄4 Complete set of design plans and special provisions 

3⁄4 “As-built” shop plans for the structural steel, architectural, mechanical, 

electrical, and hydraulic 

3⁄4 Machinery Maintenance Manual 

3⁄4 Electrical Maintenance Manual 

3⁄4 Hydraulic Maintenance Manual 

3⁄4 Copy of maintenance procedures being followed 

3⁄4 Copy of the latest Operator's Instruction being followed 

3⁄4 Copies of all inspection reports 

3⁄4 Copy of all maintenance reports 

3⁄4 Copy of all repair plans 

3⁄4 Up-to-date running log on all spare parts that are available, on order, or 

out of stock 

Inspection and maintenance reports should be reviewed with preventative 

maintenance measures in mind. An example would be the “megger” readings on 

wiring insulation; especially those taken on damp rainy days when moisture could 

influence (reduce) the values. An acceptable minimum reading is usually 1 

megohm. If the value on a wire is decreasing on progressive reports, preventative 

maintenance may save a “short” that could burn out equipment and put the bridge 

out of operation. 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.60 

Inspection and 

Maintenance Data 

Examples of inspection and maintenance records that should be kept are shown in 

Figures 12.2.68 through 12.2.74. 

Figure 12.2.68 Example of Notes on Operating Machinery (Gears-General) 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.61 

Figure 12.2.69 Example of Notes on Operating Machinery (Gears-Teeth)
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.62 

Figure 12.2.70 Example of Notes on Operating Machinery (Bearings)
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.63 

Figure 12.2.71 Example of Notes on Operating Machinery (Mechanical Elements)
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.64 

Figure 12.2.72 Example of Notes on Electrical Equipment (Motors)
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.65 

Figure 12.2.73 Example of Notes on Electrical Equipment (Limit Switch) 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.66 

Figure 12.2.74 Example of Notes on Electrical Equipment (Megger Insulation Test of the Submarine Cables)
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.67 

12.2.18 

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

inspection of movable bridges. 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 the NBI rating guidelines, a 1-digit code on the Federal Structure Inventory 

and Appraisal (SI&A) sheet indicates the condition of the superstructure. Rating 

codes range from 9 to 0 where 9 is the best rating possible. See Topic 4.2 (Item 

59) for additional details about NBI Rating Guidelines. 

The previous inspection data should be used along with current inspection findings 

to determine the correct rating. 

Element Level Condition 

State Assessment 

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

CoRe element is: 

Element No. Description

Box Girder

101 Unpainted Steel Closed Web/Box Girder 

102 Painted Steel Closed Web/Box Girder 

Floor System

106 Unpainted Steel Open Girder/Beam 

107 Painted Steel Open Girder/Beam 

112 Unpainted Steel Stringer(Stringer-Floorbeam System) 

113 Painted Steel Stringer(Stringer-Floorbeam System) 

Steel Truss

120 Unpainted Steel Thru truss (Bottom Chord) 

121 Painted Steel Thru truss (Bottom Chord) 

125 Unpainted Steel Thru Truss (Excluding Bottom Chord) 

126 Painted Steel Thru Truss (Excluding Bottom Chord) 

130 Unpainted Steel Deck Truss 

131 Painted Steel Deck Truss 

Steel Arch

140 Unpainted Steel Arch 

141 Painted Steel Arch 

Cable

146 Unpainted Steel Cable (not embedded in concrete) 

147 Painted Steel Cable (not embedded in concrete) 

Floor System

151 Unpainted Steel Floorbeam 

152 Painted Steel Floorbeam 

The unit quantity for the arch is meters or feet and the total length of the arch ribs 

must be distributed among the four available condition states for unpainted and 

five available condition states for painted structures depending on the extent and 

severity of deterioration. The unit quantity for the floor system, box girder and 

truss is meters or feet and the total length must be distributed among the 4 or 5 

available condition states. The unit quantity for cables is each and the total 

quantity must be placed in one of the four available condition states for unpainted 
SECTION 12: Special Bridges 

TOPIC 12.2: Movable Bridges 

12.2.68 

and five available condition states for painted. Condition State 1 is the best 

possible rating. See the AASHTO Guide for Commonly Recognized (CoRe) 

Structural Elements for condition state descriptions. 

A Smart Flag is used when a specific condition exists, which is not described in 

the CoRe element condition state. The severity of the damage is captured by 

coding the appropriate Smart Flag condition state. The Smart Flag quantities are 

measured as each, with only one each of any given Smart Flag per bridge. 

For damage due to fatigue, the “Steel Fatigue” Smart Flag, Element No. 356, can 

be used and one of the three condition states assigned. For rusting between riveted 

members, the “Pack Rust” Smart Flag, Element No. 357, can be used and one of 

the four condition states assigned. For damage due to traffic impact, the “Traffic 

Impact” Smart Flag, Element No. 362, can be used and one of the three condition 

states assigned. For girders/beams with section loss due to corrosion, the “Section 

Loss” Smart Flag, Element No. 363, can be used and one of the four condition 

states assigned. 

For mechanical, electrical, and hydraulic movable bridge members, individual 

bridge owners may choose to create their own non-CoRe elements.