8.7-i

Table of Contents

Section 8 ..................................................................................................................................................

Inspection and 

Evaluation of 

Common Steel 

Superstructures 

 8.7 Steel Eyebars ..................................................................................... 8.7.1 

 

 8.7.1 Introduction............................................................................... 8.7.1 

 

 8.7.2 Design Characteristics............................................................... 8.7.5 

 Development of Steel Eyebars ........................................... 8.7.5 

 Forging ............................................................................... 8.7.7 

 Hammering .................................................................. 8.7.7 

 Pressing........................................................................ 8.7.7 

 Pin Hole.............................................................................. 8.7.8 

 Heat Treating and Annealing.............................................. 8.7.9 

 Dimensions......................................................................... 8.7.9 

 Packing ............................................................................. 8.7.10 

 Spacers.............................................................................. 8.7.11 

 Redundancy...................................................................... 8.7.11 

 8.7.3 Overview of Common Defects ............................................... 8.7.12 

 8.7.4 Inspection Procedures and Locations...................................... 8.7.12 

 Procedures ........................................................................ 8.7.13 

 Visual......................................................................... 8.7.13 

 Physical...................................................................... 8.7.13 

 Advanced Inspection Techniques .............................. 8.7.13 

 Locations .......................................................................... 8.7.14 

 Forge Zone................................................................. 8.7.14 

 Tension Zone ............................................................. 8.7.14 

 Alignment .................................................................. 8.7.15 

 Areas that Trap Water and Debris.............................. 8.7.17 

 Spacers....................................................................... 8.7.17 

 Areas Exposed to Traffic ........................................... 8.7.18 

 Load Distribution....................................................... 8.7.19 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.7: Steel Eyebars 

8.7-ii

 Weldments ................................................................. 8.7.20 

 Turnbuckles................................................................ 8.7.21 

 Pins............................................................................. 8.7.22 

 Fracture Critical Members ......................................... 8.7.22 

 

 8.7.5 Evaluation ............................................................................... 8.7.23 

 NBI Rating Guidelines ..................................................... 8.7.24 

Element Level Condition State Assessment..................... 8.7.24 
8.7.1 

Topic 8.7 Steel Eyebars 

8.7.1 

Introduction Eyebars are tension only members that require pins to make their end connections. 

Eyebars are predominantly found on older truss bridges, but can also be found on 

suspension chain bridges and as anchorage bars embedded within the substructures 

of long span bridges (see Figures 8.7.1 to 8.7.4). 

Figure 8.7.1 Typical Eyebar Tension Member on a Truss 

Figure 8.7.2 Eyebar Cantilevered Truss Bridge (Queensboro Bridge, NYC) 
 SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.7: Steel Eyebars 

8.7.2 

Figure 8.7.3 Eyebar Chain Suspension Bridge 

Figure 8.7.4 Anchorage Eyebar 
 SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.7: Steel Eyebars 

8.7.3 

Heat treated steel eyebars have been used in bridges all over the world. One of 

these eyebars failed on December 15, 1967, sending the Point Pleasant Bridge 

(Silver Bridge), built in 1928, into the Ohio River between Point Pleasant, West 

Virginia and Kanauga, Ohio (see Figure 8.7.5). Forty-six people died and nine 

were injured due to the fracture of an eyebar in the north suspension chain on the 

Ohio side. 

Figure 8.7.5 Collapsed Silver Bridge 

Since the collapse of the Silver Bridge, there has been considerable public and 

professional concern over the safety of existing bridges, especially those 

containing eyebars. Many of these structures have been inspected and analyzed 

(see Figure 8.7.6). As a result, costly structural modifications and retrofits were 

made to many of these bridges (see Figure 8.7.7), while some others have been 

demolished. Eyebars are rarely used in new bridge designs but are present on 

many existing bridges. 
 SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.7: Steel Eyebars 

8.7.4 

Figure 8.7.6 Inspection of Eyebars 

Figure 8.7.7 Retrofit of Eyebars to Add Redundancy 

The design of the eyebar connections does not allow for inspection by common 

techniques. These connections collect water and promote corrosion at the critical

point on the eyebar head (see Figure 8.7.8). 
 SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.7: Steel Eyebars 

8.7.5 

Figure 8.7.8 Eyebar Connection with Corrosion 

8.7.2 

Design 

Characteristics 

Development of Steel 

Eyebars 

In the late 1800’s and early 1900’s bridge spans began to increase in length, 

providing a need for higher strength steel. Prior to this time eyebars were made of 

wrought iron. The Eads Bridge in St. Louis, completed in 1874, was the first major 

steel bridge in America and the first in the world to use alloy steel. (see Figure 

8.7.9). 
 SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.7: Steel Eyebars 

8.7.6 

Figure 8.7.9 Eads Bridge, St. Louis 

Nickel alloy steel eyebars were developed around 1900. Nickel steel showed high 

physical properties with a yield point of 380 MPa (55,000 psi) and an ultimate 

strength of 620 MPa (90,000 psi). The major disadvantage of this steel was that it 

cost 2-1/2 cents per pound more than common carbon steel. Nickel steel was also 

difficult to roll without surface defects. 

Sometime around 1915 mild grade heat treated steel eyebars (basically a “1035” 

steel) were developed with an ultimate strength of 550 MPa (80,000 psi) and a 

yield point of 345 MPa (50,000 psi). These eyebars were only 1 cent more per 

pound than common carbon steel. 

In 1923 a high tension, mild grade heat treated steel eyebar was developed. The 

guaranteed minimum ultimate strength of 725 MPa (105,000 psi) and minimum 

yield point of 515 MPa (75,000 psi) made these bars equal to wire cable with 

added stiffness but no added cost. These “1060” steel eyebars were used on the 

Silver Bridge. 

These heat treated alloy steels were extremely strong and contributed to substantial 

cost savings, but they could not be easily welded. 
 SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.7: Steel Eyebars 

8.7.7 

Forging The ends of the eyebar shanks are connected by forging. Forging is a method of 

hot working to form steel by using hammering or pressing techniques. 

Hammering 

Hammering was the first method employed in shaping metals. An early form of 

the eyebar, shaped in this manner, is known as a loop rod (see Figures 8.7.10 and 

8.7.11). Loop rods were first made of wrought iron, and later steel, by forging a 

heated bar around a pin, pounding the bar until a closed loop was formed. 

Pin

Forge

Shank

Eyebar 

Head

Figure 8.7.10 Forged Loop Rod 

Figure 8.7.11 Close-up of the End of a Loop Rod 

 Pressing 

Steel eyebars were also formed with a special type of mechanical forge press 
 SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.7: Steel Eyebars 

8.7.8 

called an upsetting machine. The eyebar consists of the two heads (formed by 

casting) joined to the ends of the shaft. The upsetting machine clamps the eyebar 

pieces between two dies with vertical faces. The eyebar is then forged and shaped 

by the horizontal action of a ram operated by a crankshaft (see Figure 8.7.12). 

Most other forging presses operate with vertical rams. 

Pin

Rolled Shank Bar

Forge

Cast Eyebar 

Head

Figure 8.7.12 Forged Eyebar 

Pin Hole The pin hole in the enlarged head of the eyebar is commonly formed by boring. 

To fabricate the hole, flame cutting is permitted to within 50 mm (2 inches) of the 

pin diameter (see Figure 8.7.13). 

Figure 8.7.13 Eyebar Pin Hole (Disassembled Connection) 
 SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.7: Steel Eyebars 

8.7.9 

Heat Treating and 

Annealing 

The inspector may find the terms “heat treated” and “annealed” on bridge plans to 

describe eyebars. Heat treating of steel is an operation in which the steel is heated 

and cooled, under controlled conditions according to a predetermined schedule, for 

the purpose of obtaining certain desired properties. 

Through heat treatment various characteristics of steel can be enhanced. If steel is 

to be formed into intricate shapes, it can be made very soft and ductile by heat 

treatment. On the other hand, if it is to resist wear, it can be heat treated to a very 

hard, wear-resisting condition. 

Annealing is a term used to describe several types of heat treatment which differ 

greatly in procedure yet all accomplish one or more of the following effects: 

3⁄4 Remove internal stresses 

3⁄4 “Soften”, by altering mechanical properties 

3⁄4 Redefine the grain structure 

3⁄4 Produce a definite microstructure 

More than one of these effects can often be obtained simultaneously. 

Dimensions The dimensions of a typical eyebar are as follows: 

3⁄4 Thickness - usually 25 to 50 mm (1 to 2 inches) 

3⁄4 Width - usually 200 to 400 mm (8 to 16 inches) 

3⁄4 Length - varied with bridge design

Length

Width

Thickness

Figure 8.7.14 Eyebar Dimensions 

The eyebars on the Silver Bridge were between 13.7 to 16.8 m (45 and 55 feet) in 

length, 300 mm (12 inches) wide, and varied in thickness. 
 SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.7: Steel Eyebars 

8.7.10 

Packing Packing is the term used to describe the arrangement of all the eyebars at a given 

point. Eyebars may be tightly packed together or spread apart (see Figures 8.7.15 

and 8.7.16). The packing should be symmetrical about the center-line of the 

member. 

Figure 8.7.15 Loosely Packed Eyebar Connection 

Figure 8.7.16 Tightly Packed Eyebar Connection 
 SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.7: Steel Eyebars 

8.7.11 

Spacers Spacers or steel filling rings are often wrapped around the pin to prevent lateral 

movement within the eyebar pack (see Figure 8.7.17). 

Figure 8.7.17 Steel Pin Spacer or Filling Ring 

Redundancy An internally redundant eyebar member will consist of three or more eyebars. 

Many eyebar members are internally non-redundant, having only one or two 

eyebars per member (see Figure 8.7.18). 

The collapse of the Silver Bridge is attributed to the failure of an eyebar within a 

nonredundant eyebar member. When the first eyebar failed, the second eyebar 

was unable to carry the load due to lack of internal redundancy. The Silver 

Bridge was also not load path redundant which contributed to the complete 

collapse of the structure. Load path and internal (member) redundancy are

discussed in detail in Topics P.2 and 8.1. 
 SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.7: Steel Eyebars 

8.7.12 

Figure 8.7.18 Nonredundant Eyebar Member 

8.7.3 

Overview of 

Common Defects 

Common defects that occur on steel multi-beam and fabricated multi-girder 

bridges are: 

3⁄4 Paint failures 

3⁄4 Corrosion 

3⁄4 Fatigue cracking 

3⁄4 Collision damage 

3⁄4 Overloads 

3⁄4 Heat damage 

See 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. 

8.7.4 

Inspection 

Procedures and 

Locations 

Inspection procedures to determine other causes of steel deterioration are 

discussed in detail in Topic 2.3.8. 
 SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.7: Steel Eyebars 

8.7.13 

Procedures Visual 

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

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

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

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

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

from the suspect area. 

Physical 

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

depending on the size and location of the suspected defect. The use of degreasing 

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

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

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

compare it to a similar section with no section loss. 

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

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

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

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

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

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

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

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

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

made. 

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

other similar locations and details. 

Advanced Inspection Techniques 

Several advanced techniques are available for steel inspection. 

Nondestructive methods, described in Topic 13.3.2, include: 

3⁄4 Acoustic emissions testing 

3⁄4 Computer programs 

3⁄4 Computer tomography 

3⁄4 Corrosion sensors 

3⁄4 Smart paint 1 

3⁄4 Smart paint 2 

3⁄4 Dye penetrant 

3⁄4 Magnetic particle 
 SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.7: Steel Eyebars 

8.7.14 

3⁄4 Radiographic testing 

3⁄4 Robotic inspection 

3⁄4 Ultrasonic testing 

3⁄4 Eddy current 

Other methods, described in Topic 13.3.3, include: 

3⁄4 Brinell hardness test 

3⁄4 Charpy impact test 

3⁄4 Chemical analysis 

3⁄4 Tensile strength test 

Locations Forge Zone 

Inspect carefully the forged area around the eyebar head and the shank for cracks. 

Check the loop rods for cracks where the loop is formed (see Figure 8.7.19). Most 

eyebar failures are likely to occur in the forge zone. 

Figure 8.7.19 Close-up of the Forge Zone on an Eyebar (Arrow denotes crack) 

 Tension Zone 

Since an eyebar carries axial tension, the entire length must be closely examined 

for deficiencies that can initiate a crack. These deficiencies include notch effects 

due to mill flaws, corrosion or mechanical damage. The area around the eye and 

the transition to the shank where stress is the highest is the most critical. 
 SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.7: Steel Eyebars 

8.7.15 

 Alignment 

Check the alignment of the shank along the full length of the eyebar. Since the 

eyebar is a tension member, it should be straight. A bowed eyebar indicates that a 

compressive force has been introduced (see Figure 8.7.20). 

Figure 8.7.20 Bowed Eyebar Member 

Misalignment due to buckling can also be caused by movement at the substructure 

or changes in loading during rehabilitation (see Figures 8.7.21and 8.7.22). The 

eyebars of the same member should be parallel and evenly loaded. 
 SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.7: Steel Eyebars 

8.7.16 

Figure 8.7.21 Buckled Eyebar due to Abutment Movement 

Figure 8.7.22 Non-parallel Eyebar Member 
 SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.7: Steel Eyebars 

8.7.17 

 Areas That Trap Water and Debris 

Areas that trap water and debris can result in active corrosion cells that can cause 

notches susceptible to fatigue or perforation and loss of section. On eyebar 

members, check the area between the eyebars especially if they are closely spaced.

 Spacers 

Examine the spacers on the pins to be sure they are holding the eyebars in their 

proper position (see Figure 8.7.23). 

Figure 8.7.23 Corroded Spacer 

Examine closely spaced eyebars at the pin for corrosion build-up (packed rust). 

These areas do not always receive proper maintenance due to their inaccessibility. 

Extreme pack rust can deform retainer nuts or cotter pins and push the eyebars off 

the pins. 

Verify the eyebars are symmetrical about the central plane of the spacer (see 

Figure 8.7.24).
 SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.7: Steel Eyebars 

8.7.18 

Figure 8.7.24 Symmetry at an Eyebar Connection 

 Areas Exposed to Traffic 

Check underneath the bridge for collision damage if the bridge crosses over a 

highway, railway, or navigable channel. Document any cracks, section loss, or 

distortion found. On a suspension bridge using eyebars, investigate the eyebars 

along the curb lines and at the ends for collision damage. 
 SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.7: Steel Eyebars 

8.7.19 

 Load Distribution 

Check to determine if any eyebars are loose (unequal load distribution) or if they 

are frozen at the ends - preventing free rotation (see Figure 8.7.25). Check for 

panel point pins or eyebar twisting. 

Figure 8.7.25 Eyebar Member with Unequal Load Distribution 

Detail A 

Detail A 
 SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.7: Steel Eyebars 

8.7.20 

 Weldments 

Evaluate the integrity of any welded repairs to the eyebar (see Figure 8.7.26). 

Check for any unauthorized welds and include their locations in your report so that 

the engineer can analyze the severity of their effect on the member (see Figure 

8.7.27). Most of these bridges are old and constructed of steel which is considered 

“unweldable” by today’s standards. It is difficult to obtain a high quality “field” 

weld. 

Figure 8.7.26 Welds on Loop Rods 

Figure 8.7.27 Welded Repair to Loop Rods 
 SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.7: Steel Eyebars 

8.7.21 

 Turnbuckles 

Examine any threaded rods in the area of the turnbuckle for corrosion, wear and 

repairs. Turnbuckles are often located in counter diagonals (see Figures 8.7.28 and 

8.7.29). 

Figure 8.7.28 Turnbuckle on a Truss Diagonal 

Figure 8.7.29 Welded Repair to Turnbuckles 
 SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.7: Steel Eyebars 

8.7.22 

 Pins 

Pins should be inspected for signs of wear and corrosion. Nondestructive methods 

such as ultrasonic inspection are recommended since visual inspection cannot 

reveal internal material flaws that may exist (see Figure 8.7.30). 

Figure 8.7.30 Ultrasonic Inspection of Eyebar Pin 

Fracture Critical Members 

Eyebars are normally used on truss or suspension bridges. Since these bridge 

types normally only have two load paths between substructure supports, the 

bridges are considered non-load path redundant. If a steel eyebar member in 

tension fails causing a total or partial collapse of the bridge, that eyebar is 

considered a fracture critical member. Truss members that have three or more 

eyebars between panel points may be considered internally redundant (see Figures

8.7.31 and 8.7.32). See Topic 8.1 for a detailed discussion on fracture critical 

members and types of redundancy. 
 SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.7: Steel Eyebars 

8.7.23 

Figure 8.7.31 Fracture Critical Bottom Chord Truss Member: Internally Nonredundant Eyebar 

Figure 8.7.32 Fracture Critical Top Chord Truss Member: Internally 

Redundant Eyebar 

8.7.5 

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 
 SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.7: Steel Eyebars 

8.7.24 

NBI Rating Guidelines Under the NBI rating guidelines, the steel eyebars are considered part of the 

superstructure and do not have an individual rating. The rating for the 

superstructure should take into account the condition of the steel eyebar assembly 

and may be lowered due to a deficiency in the steel eyebars. The superstructure is 

still rated as a whole unit but the steel eyebars may be the determining factor in the 

given rating. 

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 considered along with current inspection 

findings to determine the correct rating. 

Element Level Condition 

State Assessment 

Element level evaluation does not have specific CoRe elements for steel eyebars. 

Due to this fact, individual states may choose to create their own non-CoRe 

elements or use the AASHTO CoRe elements that “best describe” the steel 

eyebars. In an element level condition state assessment of steel eyebars, the 

AASHTO CoRe elements that relate closest to a steel eyebar include: 

Element No. Description

Truss 

121 Thru Truss (Bottom Chord) – Painted Steel 

126 Thru Truss (Excluding Bottom Chord) – Painted Steel 

131 Deck Truss – Painted Steel 

Cable 

147 Cable Coated (for suspension bridges using eyebars) 

The unit quantity for steel eyebars in truss bridges is meters or feet, and the total 

length must be distributed among the five available condition states for painted 

steel depending on the extent and severity of deterioration. The unit quantity for 

steel eyebars used as cables in suspension bridges is each and must be placed in 

one of the five available condition states for coated steel cables. 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 

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

used and one of the four condition states assigned. 
8.8-i

Table of Contents

Section 8 ..................................................................................................................................................

Inspection and 

Evaluation of 

Common Steel 

Superstructures 

 8.8 Steel Arches ........................................................................................... 8.8.1 

 

 8.8.1 Introduction............................................................................... 8.8.1 

 

 8.8.2 Deck Arch Design Characteristics ............................................ 8.8.2 

 General ............................................................................... 8.8.2 

 Primary and Secondary Members ...................................... 8.8.6 

 Load Transfer ..................................................................... 8.8.7 

 Fracture Critical Members.................................................. 8.8.7 

 

 8.8.3 Through Arch Design Characteristics....................................... 8.8.8 

 General ............................................................................... 8.8.8 

 Primary and Secondary Members ...................................... 8.8.9 

 Load Transfer ................................................................... 8.8.10 

 Fracture Critical Members................................................ 8.8.10 

 

 8.8.4 Tied Arch Design Characteristics ........................................... 8.8.11 

 General ............................................................................. 8.8.11 

 Primary and Secondary Members .................................... 8.8.12 

 Load Transfer ................................................................... 8.8.13 

 Fracture Critical Members................................................ 8.8.13 

 

 8.8.5 Overview of Common Defects ............................................... 8.8.13 

 8.8.6 Inspection Procedures and Locations...................................... 8.8.13 

 Procedures ........................................................................ 8.8.13 

 Visual......................................................................... 8.8.13 

 Physical...................................................................... 8.8.13 

 Advanced Inspection Techniques .............................. 8.8.14 

 Locations .......................................................................... 8.8.15 

 Bearing Area .............................................................. 8.8.15 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.8: Steel Arches 

8.8-ii

 Arch Members ........................................................... 8.8.15 

 Bracing (Through and Tied Arches) .......................... 8.8.15 

 Spandrel Members (Deck Arch) ................................ 8.8.16 

 Hangers (Through and Tied Arches) ......................... 8.8.16 

 Floor System.............................................................. 8.8.17 

 Tied Arches................................................................ 8.8.18 

 Tied Girder................................................................. 8.8.18 

 Fatigue Prone Details................................................. 8.8.19 

 Out-of-plane Distortion.............................................. 8.8.20 

 Secondary Members................................................... 8.8.21 

 Areas Exposed to Traffic ........................................... 8.8.22 

 Areas Exposed to Drainage........................................ 8.8.22 

 

 8.8.7 Evaluation ............................................................................... 8.8.22 

 NBI Rating Guidelines ..................................................... 8.8.22 

 Element Level Condition State Assessment..................... 8.8.23
8.8.1 

Topic 8.8 Steel Arches 

8.8.1 

Introduction Arches are a unique form of bridge in that they look like a half circle or ellipse, 

turned upside down. Arch bridges have been built since Roman times, but steel 

arch bridges have only been constructed since the late 1800’s. Arch bridges 

generally need strong foundations to resist the large concentrated diagonal loads. 

Arches are divided into three types: deck, through, and tied (see Figures 8.8.1, 

8.8.2, and 8.8.3). 

Figure 8.8.1 Deck Arch Bridge 

Figure 8.8.2 Through Arch Bridge 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.8: Steel Arches 

8.8.2 

Figure 8.8.3 Tied Arch Bridge 

8.8.2 

Deck Arch Design 

Characteristics 

General Arches are considered to be “simple span” because of the basic arch function, even 

though many bridges of this type consist of multiple arches. The arch reactions, 

with their massive horizontal thrusts, are diagonally oriented and transmitted to the 

foundation. 

Like its concrete counterpart, the steel open spandrel arch is designed to resist a 

load combination of axial compression and bending moment. The open spandrel 

steel arch is considered a deck arch since the roadway is above the arches (see 

Figure 8.8.4). The area between the arches and the roadway is called the spandrel. 

Open spandrel steel arches receive traffic loads through spandrel bents that support 

a deck and floor system. Steel deck arches can be used in very long spans, 

measuring up to 518 m (1700 ft). 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.8: Steel Arches 

8.8.3 

Figure 8.8.4 Deck Arch 

The arch members are called ribs and can be fabricated into I-girders, boxes, or 

truss shapes. The arches are classified as either solid ribbed, braced ribbed, or 

spandrel braced (see Figures 8.8.5 and 8.8.6). The members are fabricated using 

riveted, bolted, or welded techniques. Most steel deck arches have two arch rib 

members, although some structures have three or more ribs (see figure 8.8.7). 

Figure 8.8.5 Solid Ribbed Deck Arch 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.8: Steel Arches 

8.8.4 

Figure 8.8.6 Braced Rib Deck Arch, New River Gorge, WV 

Figure 8.8.7 Spandrel Braced Deck Arch with Six Arch Ribs 

An arch with a pin at each end of the arch is called a two-hinged arch (see Figure 

8.8.8). If there is also a pin at the crown, or top, of the arch, it is a three-hinged 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.8: Steel Arches 

8.8.5 

arch. One-hinged and fixed arches may exist, although these are very rare. 

Foundation conditions, in part, dictate the requirements for hinges. Three-hinged 

arches, for example, are not significantly affected by small foundation movements.

Figure 8.8.8 Hinge Pin at Skewback for Spandrel Braced Deck Arch (Navajo 

Bridge) 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.8: Steel Arches 

8.8.6 

Primary and Secondary 

Members 

The primary members of a deck arch bridge consist of the arches or ribs, spandrel 

columns or bents, spandrel girders and the floor system. The floor system consists 

of floorbeams and stringers (if present) (see Figure 8.8.9). 

The secondary members of a deck arch bridge consist of the sway bracing and the 

upper lateral and lower lateral bracing of the arch or floor system (see Figure 

8.8.10).

Figure 8.8.9 Solid Ribbed Deck Arch Primary Members

Figure 8.8.10 Solid Ribbed Deck Arch Secondary Members

D 

C B 

A 

E 

A 

B 

Primary Members

A – Spandrel girders 

B – Stringers 

C – Floorbeam or spandrel bent cap 

D – Spandrel columns 

E – Arch rib 

Secondary Members

A – Sway bracing 

B – Lower lateral bracing 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.8: Steel Arches 

8.8.7 

Load Transfer Traffic loads are supported by a deck. The load from the deck is transmitted to the 

stringers (if present) and then the floorbeams. The stringer and floorbeams resist 

the traffic load in bending and shear. The load is transferred to the spandrel bents 

and spandrel columns, which are in compression or bending. The arch supports 

the spandrel column and transfers the compressive load to the ground at the 

supports. 

Fracture Critical 

Members 

The deck arch bridge has two or more main members. However, the arch is not a 

tension member and is therefore not considered fracture critical. Some members 

of the floor system and spandrel bent may be considered fracture critical (see 

Topic 8.3) 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.8: Steel Arches 

8.8.8 

8.8.3 

Through Arch 

Design 

Characteristics 

General Arch bridges are considered simple spans because of the basic arch function, even 

though many bridges of this type consist of multiple arches. Through arches are 

typically two or three hinged. The arch reactions, with their massive horizontal 

thrusts, are diagonally oriented and transmitted to the foundations. 

The steel through arch is constructed with the crown of the arch above the 

roadway and the arch foundations below the roadway (see Figure 8.8.11). The 

deck is hung from the arch by wire rope cables or eyebars. 

Figure 8.8.11 Elevation View of a Braced Ribbed Through Arch 

The arch members are called ribs and are usually fabricated box-type members. 

Steel through arches are known as either solid ribbed or braced ribbed. The solid 

ribbed arch, which can be any type of arch, has a single curve defining the arch 

shape, while the braced ribbed arch has two curves defining the arch shape, braced 

with truss webbing between the curves. The lower curve is the bottom rib chord, 

and the upper curve is the top rib chord. The rib chord bracing consists of posts 

and diagonals. The braced ribbed arch is sometimes referred to as a trussed arch 

and is more common than the solid ribbed through arch. 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.8: Steel Arches 

8.8.9 

Primary and Secondary 

Members 

The primary members of a through arch bridge consist of arch ribs (consisting of 

top and bottom rib chords and rib chord bracing), rib chord bracing, hangers and 

floor system including floorbeams and stringers (if present) (see Figure 8.8.12). 

The secondary members of a through arch bridge consist of sway bracing, lateral 

bracing (top and bottom rib chords and floor system) (see Figure 8.8.13). 

Figure 8.8.12 Through Arch Primary Members 

Figure 8.8.13 Through Arch Bracing (Secondary Members)

A

B 

A

A

B

C 

A

Primary Members

A – Top and bottom rib chords 

B - Rib chord bracing 

C – Hangers 

Floor system not visible

Secondary Members

A – Lateral bracing (top and 

bottom rib chords) 

B – Sway bracing 

Lateral bracing in floor system not 

shown 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.8: Steel Arches 

8.8.10 

Load Transfer Traffic loads are supported by a deck. The load from the deck is transmitted to the 

stringers (if present) and then the floorbeams. The stringer and floorbeams resist 

the load in bending and shear. The load is transferred to the hangers, which are in 

tension. The arch supports the hangers and transfers the compressive load to the 

ground at the supports.

Fracture Critical 

Members 

The through arch is the main load-carrying member. Since there are typically only 

two arch ribs, the structure is nonredundant. However, the bridge is not classified 

as fracture critical because the arches are not tension members. The hangers may 

be fracture critical, depending on the results of a detailed structural analysis. Some 

members of the floor system may be fracture critical (see Topic 8.3). 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.8: Steel Arches 

8.8.11 

8.8.4 

Tied Arch Design 

Characteristics 

General The tied arch is a variation of the through arch with one significant difference. In 

a through arch, the horizontal thrust of the arch reactions is transferred to large 

rock, masonry, or concrete foundations. A tied arch transfers the horizontal 

reactions through a horizontal tie which connects the ends of the arch together, like 

the string on an archer’s bow (see Figure 8.8.14). The tie is a tension member. If 

the string of a bow is cut, the bow will spring open. Similarly, if the arch tie fails, 

the arch will lose its compression and will collapse. 

Design plans are generally needed to differentiate between through arches and tied 

arches. Another guide in correctly labeling through and tied arches is by 

examining the piers. Since tied arch bridges redistribute the horizontal loads to the 

tie girders, the piers for tie arch bridges are smaller than the piers for through arch

bridges. 

Figure 8.8.14 Tied Arch 

Arch members are fabricated with either solid rib members, box members or 

braced ribs. 

The tie member is a fabricated box member or consists of truss members. The tie 

is also supported by hangers, which usually consist of wire rope cable, but can also 

be eyebars or built-up members. 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.8: Steel Arches 

8.8.12 

Primary and Secondary 

Members 

The primary members of a tied arch bridge consist of arch ribs, tie members, rib 

bracing truss (if present), hangers, and floor system including floorbeams and 

stringers (if present) (see Figure 8.8.15). 

The secondary members of a tied arch bridge consist of sway bracing, lateral 

bracing (arch rib, top chord and floor system) (see Figure 8.8.16). 

Figure 8.8.15 Tied Arch Primary Members 

Figure 8.8.16 Tied Arch Secondary Members

A

B 

C 

A

B 

D 

C 

Primary Members

A – Arch ribs 

B – Hangers 

C – Tie members 

D – Floor system 

Rib bracing truss not present. 

Secondary Members

A – Lateral bracing (top) 

B – Sway bracing 

C – Portal bracing 

Lateral bracing in the 

floor system not shown 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.8: Steel Arches 

8.8.13 

Load Transfer Traffic loads are supported by a deck. The load from the deck is transmitted to the 

stringers (if present) and then the floorbeams. The stringer and floorbeams resist 

the load in bending and shear. The load is transferred to the hangers, which are in 

tension. The arch supports the hangers and transfers the compressive load to the 

tie girder and the supports. 

Fracture Critical 

Members 

With only two load paths, arches are considered non-redundant structures. The 

arches are not fracture critical since they are subjected to axial compression. The 

tie girders, on the other hand, are axial tension members and are considered 

fracture critical. 

8.8.5 

Overview of 

Common Defects 

Common defects that occur on steel arch bridges are: 

3⁄4 Paint failures 

3⁄4 Corrosion 

3⁄4 Fatigue cracking 

3⁄4 Collision damage 

3⁄4 Overloads 

3⁄4 Heat damage 

See 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. 

8.8.6 

Inspection 

Procedures and 

Locations 

Inspection procedures to determine other causes of steel deterioration are 

discussed in detail in Topic 2.3.8. 

Procedures Visual 

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

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

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

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

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

from the suspect area. 

Physical 

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

depending on the size and location of the suspected defect. The use of degreasing 

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

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

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

compare it to a similar section with no section loss. 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.8: Steel Arches 

8.8.14 

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

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

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

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

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

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

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

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

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

made. 

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

other similar locations and details. 

Advanced Inspection Techniques 

Several advanced techniques are available for steel inspection. Nondestructive 

methods, described in Topic 13.3.2, include: 

3⁄4 Acoustic emissions testing 

3⁄4 Computer programs 

3⁄4 Computer tomography 

3⁄4 Corrosion sensors 

3⁄4 Smart paint 1 

3⁄4 Smart paint 2 

3⁄4 Dye penetrant 

3⁄4 Magnetic particle 

3⁄4 Radiographic testing 

3⁄4 Robotic inspection 

3⁄4 Ultrasonic testing 

3⁄4 Eddy current 

Other methods, described in Topic 13.3.3, include: 

3⁄4 Brinell hardness test 

3⁄4 Charpy impact test 

3⁄4 Chemical analysis 

3⁄4 Tensile strength test 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.8: Steel Arches 

8.8.15 

Locations Bearing Area 

Examine the web areas over the supports for cracks, section loss and buckling. If 

bearing stiffeners, jacking stiffeners and diaphragms are present at the supports 

inspect them for cracks, section loss and buckling also. 

Examine the bearings on each of the supports for corrosion. Check the alignment 

of each bearing and note any movement. Report any build up of debris 

surrounding the bearings that may limit the bearing from functioning properly. 

Check for any bearings that are frozen due to heavy corrosion. (see Topic 9.1). 

 Arch Members 

Inspect the alignment of the arch and look for signs of buckling and crippling in 

the arch ribs. Check for general corrosion and deterioration Examine any pins for 

corrosion and wear. Check the arch rib splice plates and the connections for 

hangers or spandrel bents. 

Inspect steel arch girder type bridges as described in Topic 8.2. Inspect steel arch 

box girder type bridges as described in Topic 8.5. Inspect steel braced ribbed arch 

type bridges as described in Topic 8.6 (see Figure 8.8.17). 

Figure 8.8.17 Through Truss Arch Members 

 Bracing (Through and Tied Arches) 

Inspect the web members (posts and diagonals) in a manner similar to any other 

truss as described in Topic 8.6. Depending on the truss design (e.g., Pratt or 

Warren, etc.), the web members will either be designed for tension, compression, 

or both. 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.8: Steel Arches 

8.8.16 

Spandrel Members (Deck Arch) 

Examine the end connections of the spandrel bents, spandrel columns and spandrel 

girders for cracks and loose fasteners. Check the spandrel girders/caps/columns 

for flexure, section loss, and buckling damage (see Figure 8.8.18). 

Figure 8.8.18 Solid Ribbed Deck Arch Showing Spandrel Columns 

 Hangers (Through and Tied Arches) 

Check the connections at both ends of the hangers, and look for corrosion and 

cracks. Examine the alignment of the hangers; the hangers may be near traffic, so 

inspect for collision or fire damage (see Figures 8.8.19 and 8.8.20). Check the 

hangers for any welded attachment; examine the welds between the attachment 

and the hanger for cracks
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.8: Steel Arches 

8.8.17 

Figure 8.8.19 Hanger Connection on a Through Arch 

Figure 8.8.20 Performing Baseline Hardness Test on Fire Damaged Arch Cables 

 Floor System 

The floor system, consisting of floorbeams and possibly stringers, should be 

inspected in the same manner as previously described in Topic 8.3, Steel Twogirder Systems & Steel Through Girder Systems (see Figure 8.8.21). 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.8: Steel Arches 

8.8.18 

Tied Arches 

Tied arches are subjected to axial compression in addition to bending caused by 

the hanger connections. Check floorbeam to tied member connection for 

distortion caused by fatigue or horizontal floorbeam displacement in the webs of 

the floorbeams when the stringers are placed above the floorbeams. 

Figure 8.8.21 Floor System on a Through Arch 

 Tied Girder 

Determine if back-up bars were used to make corner welds in the tie box. If so, 

the back-up bars should be carefully examined to determine if they are continuous. 

Weld cracks can occur at points where the bars are discontinuous. Check all 

welds, and examine the ends of any cover plates. Especially check welds 

connecting internal diaphragms to the tie box. Inspect the floorbeam connections 

and the corner welds of the tie box (see Figure 8.8.22).
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.8: Steel Arches 

8.8.19 

Fatigue Prone Details 

Check the welds on tension members such as tie girders, floorbeams or stringers. 

Look at welds for stiffeners/diaphragms/connection plates. 

If cover plates are present, look at the welded ends for cracking. Back-up bars 

may be used between the webs and flanges and are susceptible to cracking. 

Check the web gap area between the flanges and the connection plates. Closely 

inspect tack welds, intersecting welds and discontinuous or intermittent welds. 

Figure 8.8.22 Tie Girder Interior 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.8: Steel Arches 

8.8.20 

 Out-of-plane Distortion 

Investigate the girders at the floorbeam connection for cracks in the webs due to 

out-of-plane distortion. Investigate for fatigue cracks due to web-gap distortion. 

This is a major source of cracking when floorbeams frame into girders. For 

additional information on out-of-plane distortion, see Topic 8.3. 

Out-of-plane distortion can also crack the tie girder webs at partial depth 

diaphragm connection with floorbeams (see Figure 8.8.23). The diaphragms 

stiffen the tie girders. However, the small, unstiffened regions of the webs do not 

have sufficient rigidity against lateral, out-of-plane distortion. The situation is 

analogous to that of webs at unattached ends of floorbeam or diaphragm 

connection plates. Fatigue cracks can develop at the ends of the diaphragm plates. 

The ends of all partial depth diaphragms in a box tie girder should be closely 

inspected. 

Floorbeam

Tied Box Girder Web

Tied Box Girder Flange

Partial Depth Diaphragm

Areas Prone to Fatigue Cracks

Figure 8.8.23 Partial Depth Diaphragm in a Tied Box Girder 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.8: Steel Arches 

8.8.21 

 Secondary Members 

The secondary members should be inspected using methods similar to those 

detailed in Topics 8.3, 8.5, and 8.6 (see Figure 8.8.24). In addition: 

Investigate the alignment of the bracing elements. Check horizontal connection 

plates, which can trap debris and moisture and are susceptible to a high degree of 

corrosion and deterioration. Examine the end connections for cracks, corrosion, 

and loose fasteners. 

Misalignment of secondary members may be an indication of differential structure 

movement or substructure settlement. 

Figure 8.8.24 Bracing Members (New River Gorge Bridge) 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.8: Steel Arches 

8.8.22 

 Areas Exposed to Traffic 

Inspect any areas exposed to traffic for collision damage (see Figure 8.8.25). If 

collision damage is found, document the location and dimensions and reference 

with photographs or sketches.

Figure 8.8.25 Areas Exposed to Traffic 

 Areas Exposed to Drainage 

The areas that trap water and debris result in active corrosion cells, which cause 

loss of section and notches susceptible to fatigue. On arch bridges check lateral 

bracing gusset plates, pockets created by floor system connections, and areas 

exposed to drainage runoff. 

8.8.7 

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 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 considered along with current inspection 

findings to determine the correct rating. 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.8: Steel Arches 

8.8.23 

Element Level Condition 

State Assessment 

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

CoRe elements may be: 

Element No. Description

Box Girder 

101 Unpainted Steel Closed Web/Box Girder 

102 Painted Steel 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 Arch 

140 Unpainted Steel Arch 

141 Painted Steel Arch 

Hanger 

146 Cable (not embedded in concrete) Uncoated 

147 Cable (not embedded in concrete) Coated 

Floor System

151 Unpainted Steel Floorbeam 

152 Painted Steel Floorbeam 

Pin and Hanger 

160 Unpainted Steel Pin and Hanger Assembly 

161 Painted Steel Pin and Hanger Assembly 

Spandrel Columns 

201 Unpainted Steel Columns 

202 Painted Steel Columns 

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 is meters or feet 

and the total length of floor beams and stringers must be distributed among the 4 

or 5 available condition states. The unit quantity for columns, cables or hanger 

assemblies is each and the total quantity must be placed in one of the four 

available condition states for unpainted 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 rust 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 steel arches 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. 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.8: Steel Arches 

8.8.24 

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8.9-i

Table of Contents

Section 8 ..................................................................................................................................................

Inspection and 

Evaluation of 

Common Steel 

Superstructures 

 8.9 Steel Rigid Frames................................................................................. 8.9.1 

 

 8.9.1 Introduction............................................................................... 8.9.1 

 

 8.9.2 Design Characteristics............................................................... 8.9.1 

 General ............................................................................... 8.9.1 

 K-Frames ..................................................................... 8.9.2 

 Delta Frames ................................................................ 8.9.3 

 Stiffeners ............................................................................ 8.9.5 

 Transverse Stiffeners ................................................... 8.9.5 

 Longitudinal Stiffeners ................................................ 8.9.5 

 Radial Stiffeners........................................................... 8.9.5 

 Floor System Arrangement................................................. 8.9.6 

 Multiple Frame System................................................ 8.9.6 

 Frame-Floorbeam System............................................ 8.9.6 

 Frame-Floorbeam-Stringer System.............................. 8.9.6 

 Primary and Secondary Members ...................................... 8.9.7 

 Stress Zones........................................................................ 8.9.9 

 Fatigue Prone Details and Failure ...................................... 8.9.9 

 Fracture Critical Areas ....................................................... 8.9.9 

 

 8.9.3 Overview of Common Defects ............................................... 8.9.11 

 

 8.9.4 Inspection Procedures and Locations...................................... 8.9.11 

 Procedures ........................................................................ 8.9.11 

 Visual......................................................................... 8.9.11 

 Physical...................................................................... 8.9.11 

 Advanced Inspection Techniques .............................. 8.9.12 

 Locations .......................................................................... 8.9.13 

 Bearing Areas............................................................. 8.9.13 

 Shear Zones................................................................ 8.9.13 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.9: Steel Rigid Frames 

8.9-ii

 Flexure Zones............................................................. 8.9.14 

 Secondary Members................................................... 8.9.14 

 Areas that Trap Water and Debris.............................. 8.9.14 

 Areas Exposed to Traffic ........................................... 8.9.14 

 Fatigue Prone Details................................................. 8.9.15 

 

 8.9.5 Evaluation ............................................................................... 8.9.16 

 NBI Rating Guidelines ..................................................... 8.9.16 

 Element Level Condition State Assessment..................... 8.9.16
8.9.1 

Topic 8.9 Steel Rigid Frames 

8.9.1 

Introduction A frame is a multi-sided configuration in which the sides are rigidly connected in 

such a fashion that applied loads are distributed to each side (see Figure 8.9.1). 

Steel rigid frames are popular today in building construction because of their 

space-saving characteristics. The same principles that permit the omission of 

intermediate column supports in buildings are applied to bridge frames. In a steel 

rigid frame bridge structure, the frame sides or “legs” replace intermediate 

supports. Because the legs contribute to the structures overall capacity, increased 

span lengths and material savings can be realized. 

Figure 8.9.1 Typical Rigid K-frame Constructed of Two Frames 

8.9.2 

Design 

Characteristics 

General Frames are not referred to as having a single, simple, multiple, or continuous 

spans. Also, steel rigid frame structures are used only in straight horizontal 

applications. 

Steel rigid frame bridges typically consist of welded plate girder construction with 

bolted field splices in low stress areas and welded stiffeners in high stress areas. 

The frames are spaced from about 2 to 6 m (7 to 20 feet) on centers, depending on 

loads, span lengths, and type of floor system. Steel rigid frames can be 

economical for spans from 15 m (50 feet) to over 61 m (200 feet). Standard 

abutments and expansion bearings support the ends of the frame girders. 

The superstructure of a rigid frame bridge can be constructed of two frames similar 

to a two-girder bridge (see Figure 8.9.1) or of multiple frames in the same manner 

as a multi-girder bridge (see Figure 8.9.2). These frames can be thought of as 

fabricated girders with legs. 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.9: Steel Rigid Frames 

8.9.2 

Figure 8.9.2 Typical Rigid Frame Constructed of Multiple Frames 

 K – Frames 

Most steel rigid frame bridges are multi-span structures and are commonly referred 

to as "K-frame" or "grasshopper leg" bridges (see Figure 8.9.3). The sloping legs 

give the rigid frame a "K" shape, when looked at by rotating the frame 

counterclockwise 90°. K-frames are not economical for very short or very long 

span bridges. Because of their aesthetically pleasing appearance, sometimes an 

effort is made to use steel rigid frames whenever possible. 

Figure 8.9.3 Typical K-frame 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.9: Steel Rigid Frames 

8.9.3 

It is possible to think that the legs of the K-frame look very much like piers and 

consider them part of the substructure. This is not the case because there is no 

bearing between the legs and the girder portion of the frame (see Figure 8.9.3). 

Since there are no bearings between the legs and girder portion of the frame, 

bending forces are transferred between the girder portion and the legs (see Figure 

8.9.4). 

Figure 8.9.4 Connection Between Legs and Girder Portion 

 Delta Frames 

In some designs, a triangular frame configuration can be used. For very long 

spans, two K-frames can be connected together end-to-end (see Figure 8.9.5). 

Instead of one of the end spans bearing on an abutment, it is connected to the end 

span of another K-frame. The bottoms of the legs are also connected together and 

share the same bearing. This type of configuration is known as a delta frame. The 

leg connections form an inverted triangle with the girder portion of the frame. The 

Greek letter Delta (∇) is the symbol used for this triangle. 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.9: Steel Rigid Frames 

8.9.4 

Figure 8.9.5 Delta Frame 

Regardless of the frame configuration, the entire portion of the bridge, (legs and 

girders) constitutes the frame, and is considered the superstructure. The legs of 

rigid frames are supported by relatively small concrete footings and bearings 

which are essentially hinges (see Figure 8.9.6). 

Figure 8.9.6 Bearing 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.9: Steel Rigid Frames 

8.9.5 

Stiffeners Steel rigid frames may have up to three different types of stiffeners (see Figure 

8.9.7). 

Transverse Stiffeners 

Transverse stiffeners are placed approximately perpendicular to the flanges and 

welded to the web and flanges of the frame at spacings required by design. 

Transverse stiffeners are used to prevent buckling in high shear regions. 

Longitudinal Stiffeners 

Longitudinal stiffeners are placed parallel to the flanges and welded to the web of 

the frame. They may extend the entire length of the frame girder or just in areas of 

high moment. Longitudinal stiffeners resist web buckling in the compression zone 

and therefore are closer to the top flange in areas of higher positive moment and 

closer to the bottom flange in areas of higher negative moment. 

Radial Stiffeners 

Radial stiffeners are placed perpendicular along the frame knee bottom flange 

radius. The radial stiffeners are welded to the flange and web at spacings required 

by design. This type of stiffener is used to resist shear and moment forces in the 

knee.

Stiffeners

A – Transverse 

B – Longitudinal 

C – Radial 

Figure 8.9.7 Transverse, Longitudinal, and Radial Stiffeners on a Frame Knee 

C 

B 

A 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.9: Steel Rigid Frames 

8.9.6 

Floor System 

Arrangement 

A rigid frame will have one of three floor systems: 

Multiple Frame System 

For a multiple frame system, the deck is supported only by the frames (see Figure 

8.9.2). 

Frame-Floorbeam System 

Floorbeams are connected to the girder portion of the two frames. The floorbeams 

are much smaller than the girder portion of the frame and are perpendicular to the 

flow of traffic. The deck is supported by the floorbeams, which in turn transmit 

the loads to the frames. The floorbeams can be either rolled beams, fabricated 

girders, or fabricated cross frames. 

Frame-Floorbeam-Stringer System 

Longitudinal stringers, parallel to the frames, are connected to the floorbeams (see 

Figure 8.9.8). Floorbeams are connected to the girder portion of the two frames. 

The stringers are typically rolled sections and are connected to the web of the 

floorbeams. 

Figure 8.9.8 Two Frame Bridge with Floorbeam-Stringer Floor System 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.9: Steel Rigid Frames 

8.9.7 

Primary and Secondary 

Members 

For steel rigid frame bridges, the primary members are the frames as a whole, 

including floorbeams and stringers (if present) (see Figure 8.9.8). However, for 

ease of discussion, the frame is commonly broken down into the following five 

elements: 

3⁄4 Frame girder - the horizontal sections 

3⁄4 Frame leg - the inclined sections 

3⁄4 Frame knee - the intersection between the frame girder and frame leg 

3⁄4 Floorbeams (if present) 

3⁄4 Stringers (if present) 

The primary members consist of the frames and floor system. The frame girder, 

frame knee and frame leg make up the frame. If present, the floor system consists 

of floorbeams and stringers (see Figure 8.9.9). 

Secondary members consist of lateral bracing, sway bracing and diaphragms. 

In a two frame system, lateral bracing members are placed diagonally between the 

frames. This bracing restricts any differential and longitudinal movements 

between the frames. This bracing is in the plane of the bottom flange of the girder 

portion of the frame or between the legs of the frame (see Figure 8.9.10). 

Figure 8.9.9 Frame Members, Floorbeams, and Stringers 

STRINGER

FLOORBEAM

FRAME 

GIRDER

FRAME LEG

FRAME KNEE
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.9: Steel Rigid Frames 

8.9.8 

In a two frame system, sway bracing is placed between the leg portions of the 

frame (see Figure 8.9.10). In a multiple frame system diaphragms are placed 

perpendicular between the frames. The sway bracing and diaphragms minimize 

any transverse movements of the frames (see Figure 8.9.11). 

Figure 8.9.10 Lateral Bracing for the Frame Legs 

Figure 8.9.11 Lateral Bracing and Diaphragms 

Lateral 

Bracing 

Diaphragm 

Frame 

Sway 

Bracing

Frame 

Lateral 

Bracing
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.9: Steel Rigid Frames 

8.9.9 

Stress Zones Each element of the frame resists various levels of stress due to moment and shear. 

Tension zones are similar to those for concrete rigid frames (see Figure 8.9.12). 

Stress zones for the floor systems are similar to the two-girder floor systems 

discussed in Topic 8.3. 

Compression Zones

Shear Zones

Tension Zones

Highest at frame knee and 

substructure supports

Figure 8.9.12 Stress Zones in a Frame 

Fatigue Prone Details 

and Failure 

Some common areas for fatigue prone details are: 

3⁄4 Fabrication welds 

3⁄4 Welded cover plates 

3⁄4 Web stiffener welds 

3⁄4 Welded flange splices 

3⁄4 Intersecting welds 

3⁄4 Attachment welds located in the tension zone 

3⁄4 Web gaps 

3⁄4 Mechanical splices 

Inspection of these areas is discussed in Topic 8.9.4. 

Fracture Critical Areas A rigid frame consisting of two frames has no load path redundancy. This means 

that a two frame steel rigid frame is a fracture critical bridge type (see Figure 

8.9.13). 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.9: Steel Rigid Frames 

8.9.10 

Figure 8.9.13 Dual Frame Rigid Frame – A Fracture Critical Structure 

A rigid frame bridge consisting of three or more frames has load path redundancy 

and is not fracture critical (see Figure 8.9.14). 

Figure 8.9.14 Multiple Frame Rigid Frame – Not a Fracture Critical Structure 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.9: Steel Rigid Frames 

8.9.11 

8.9.3 

Overview of 

Common Defects 

Common defects that occur on steel rigid frame 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. 

8.9.4 

Inspection 

Procedures and 

Locations 

Inspection procedures to determine other causes of steel deterioration are 

discussed in detail in Topic 2.3.8. 

Procedures Visual 

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

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

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

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

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

from the suspect area. 

Physical 

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

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

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

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

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

compare it to a similar section with no section loss. 

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

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

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

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

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

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

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

a possible crack is to be conducted by another person, it is advisable not to disturb 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.9: Steel Rigid Frames 

8.9.12 

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

made. 

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

other similar locations and details. 

Advanced Inspection Techniques 

Several advanced techniques are available for steel inspection. 

Nondestructive methods, described in Topic 13.3.2, include: 

3⁄4 Acoustic emissions testing 

3⁄4 Computer programs 

3⁄4 Computer tomography 

3⁄4 Corrosion sensors 

3⁄4 Smart paint 1 

3⁄4 Smart paint 2 

3⁄4 Dye penetrant 

3⁄4 Magnetic particle 

3⁄4 Radiographic testing 

3⁄4 Robotic inspection 

3⁄4 Ultrasonic testing 

3⁄4 Eddy current 

Other methods, described in Topic 13.3.3, include: 

3⁄4 Brinell hardness test 

3⁄4 Charpy impact test 

3⁄4 Chemical analysis 

3⁄4 Tensile strength test 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.9: Steel Rigid Frames 

8.9.13 

Locations Bearing Areas 

Examine the floor system, frame knee area and the web areas over the supports for 

cracks, section loss or buckling. If bearing stiffeners, jacking stiffeners and 

diaphragms are present at the supports inspect them for cracks, section loss and 

buckling also. 

Examine the bearings at each support for corrosion. Check the alignment of each 

bearing and note any movement. Report any build up of debris surrounding the 

bearings that may limit the bearing from functioning properly. Check for any 

bearings that are frozen due to heavy corrosion (see figure 8.9.15). See Topic 9.1 

for a detailed presentation on the inspection of bearings. 

Figure 8.9.15 Bearing Area of a Two Frame Bridge 

 Shear Zones 

Examine the web area of the girder portion near the bearings and knee areas for 

section loss due to corrosion. Check the web area of the girder portion near the 

bearings and knee areas for buckling. Inspect floorbeams and stringers (if present) 

near their respective bearing areas for corrosion or buckling. Check the bottom of 

the frame legs for corrosion or buckling. 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.9: Steel Rigid Frames 

8.9.14 

 Flexure Zones 

Check the tension and compression flanges for corrosion, section loss, cracks or 

buckling (see Figure 8.9.16). Special attention should be given to the flanges at 

the connection between the legs and girder portion of the beam. Bending moment 

is at its highest in this area. 

Figure 8.9.16 Flexural Zones 

 Secondary Members 

Check horizontal connection plates which can trap debris and moisture and are 

susceptible to a high degree of corrosion and deterioration. Investigate the areas 

beneath drainpipes and deck joints for corrosion from exposure to roadway 

drainage. Examine the connection areas of the lateral bracing or diaphragms for 

cracked welds, fatigue cracks, and loose fasteners. Check for distortion in the 

secondary members. Distorted secondary members may be an indication the 

primary members are overstressed of the substructure may be experiencing 

differential settlement. 

 Areas that Trap Water and Debris 

The areas that trap water and debris result in active corrosion cells and can cause 

in notches susceptible to fatigue or perforation and loss of section. On rigid frame 

bridges check horizontal surfaces that include top of bottom flange, lateral bracing 

gusset plates and pockets created by floor system connections. 

 Areas Exposed to Traffic 

Check underneath the bridge for collision damage to the frame sections and 

bracing if the bridge crosses over a highway, railway, or navigable channel. 

Document any cracks, section loss, scrapes or distortion found. 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.9: Steel Rigid Frames 

8.9.15 

 Fatigue Prone Details 

Examine any attachment welds located in the tension areas of the frame or floor 

system. Check web stiffener welds. Pay close attention to the knee area. Vertical, 

longitudinal, and radial stiffeners may all be present, and there may be a possibility 

of intersecting welds (see Figure 8.9.17). Inspect welded flange splices, 

particularly where changes in thickness and/or width occur (see Figure 8.9.18).

Figure 8.9.17 Knee Area: Fatigue Prone Details 

Figure 8.9.18 Welded Flange Splice 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.9: Steel Rigid Frames 

8.9.16 

8.9.5 

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 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 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 

The element level method does not have specific CoRe elements for steel rigid 

frames. Due to this fact, individual states may choose to create their own nonCoRe elements or use the AASHTO CoRe elements that “best describe” the rigid 

frame. In an element level condition state assessment of a steel rigid frame bridge, 

the AASHTO CoRe elements that relate closest to a rigid frame include: 

Element No. Description

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) 

151 Unpainted Steel Floorbeam 

152 Painted Steel Floorbeam 

201 Unpainted Steel Column or Pile Extension 

202 Painted Steel Column or Pile Extension 

The unit quantity for the rigid frame is meters or feet, and the total length 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 columns is each and the total 

quantity 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. 

For states that create their own non-CoRe elements, the bridge inspector must use 

that particular state’s Bridge Inspection Manual to determine the appropriate nonCoRe element(s) as well as the correct condition state(s). 

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 to fatigue, the “Steel Fatigue” Smart Flag, Element No. 356, can be 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.9: Steel Rigid Frames 

8.9.17 

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 steel rigid frames 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. 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.9: Steel Rigid Frames 

8.9.17 

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 steel rigid frames 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. 
SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.9: Steel Rigid Frames 

8.9.18 

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SECTION 8: Inspection and Evaluation of Common Steel Superstructures 

TOPIC 8.9: Steel Rigid Frames 

8.9.18 

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