Hanging by a Thread: The Life of a Bridge Inspector

Those who crave security and comfort need not apply

Published: Monday, December 12, 2022 - 13:02

Yup, that’s me in the photo. You’re probably wondering how I ended up hanging under a bridge over the Mississippi River. I’m a certified bridge safety inspector.

If you have questions after seeing people hanging under a bridge, in a basket suspended from the long arm of a truck, or have seen people crawling over the steel structure with seemingly nothing preventing them from falling off, I’ve got some answers.

After a long ride in a windowless van with 10 other people into the middle of Louisiana, a scramble over a barrier, I go down a ladder to get on a pier of the Horace Wilkinson Bridge on Interstate I-10, which carries traffic in and out of Baton Rouge. In order for it to continue to do so, the bridge will undergo a rigorous inspection. Our team will spend the next two weeks climbing and crawling over every single inch of the 54-year-old “new bridge,” as it is referred to by locals.

There’s nothing glamorous about bridge inspection—especially during July in Louisiana—but, in the interest of public safety, we carry on.

Making my way out of a shallower floor beam using beam clamps

Routine bridge inspections identify defects that professionals report back to state transportation agencies and commissions to facilitate key funding and maintenance decisions. It was a routine bridge inspection that found a nearly completely severed in-tension member of the Hernando de Soto Bridge in Memphis, Tennessee, last year. If that member had failed, the entire bridge could have collapsed. A fracture-critical bridge inspection requires that every part of a bridge receive “hands-on” inspection, meaning the inspector must get within an arm’s length of every structural member.

Not a bad view of the city: The dual Greater New Orleans bridges from the highest tower peak of the structure.

Origins of the Federal Bridge Inspection Program

As is the case with most federal policies and regulations, the National Bridge Inspection Program and Standards came about because of a preventable tragedy. On December 15, 1967, the Silver Bridge over the Ohio River connecting Point Pleasant, West Virginia, and Gallipolis, Ohio, collapsed during the height of rush hour. Forty-six people lost their lives. The bridge had been constructed in 1928 and featured nonredundant eyebars in tension. High-strength steel was used in the eyebars, which gave the impression that the typical four- or six-eyebar chain wasn’t required.

From a pure strength standpoint, the Silver Bridge was sufficient to carry the loads for which it was originally designed. The structure was built during a time when the standard family vehicle, the Model T, weighed 1,500 lb. When the bridge collapsed, the average vehicle weight had ballooned to 4,000 lb, and vehicle traffic had greatly increased. Deterioration over the life of the bridge had left one of the eyebars cracked and structurally compromised. When it finally gave out, the load transferred to its partner, which also fractured.

Taking notes while completing inspection of the bridge’s top chord

The Silver Bridge disaster was the first high-profile bridge collapse in the United States during the rise of automobile ownership and the creation of the National Highway System. The Tacoma Narrows Bridge in the state of Washington had famously collapsed in 1940, but there were no fatalities. Naturally, the failure in Memphis, which came at a time when Americans had taken to automobiles in large numbers, drew intense scrutiny. Congress acted immediately (that must be nice) and passed the Federal-Aid Highway Act in 1968, establishing a set of standards for bridge inspection and requiring states to maintain written inspection reports.

By 1971, further legislation had ironed out the details of the federal bridge inspection standards that became the National Bridge Inspection Standards (NBIS) and remain in place today. Under NBIS, structures longer than 20 ft that are part of the federally aided highway system must be inspected every two years. These structures form the original National Bridge Inventory. During the past 50 years, the program has continued to evolve and was expanded to encompass all structures on public roads in 1979. Further guidance on the inspection of fracture-critical bridges was passed into law in 1988, prompted by the 1983 collapse of the Mianus River Bridge in Connecticut. The 2007 collapse of the I-35 bridge over the Mississippi River in Minneapolis was caused by the failure of a gusset plate, prompting a nationwide push for a more thorough inspection and load ratings process for specific components of truss bridges.

The NBIS program has been in place for more than 50 years and has been largely successful. In the rare case of bridge failure in the U.S., reaction is typically swift and aggressive. Funding, however, remains a major concern. This was apparent with the collapse of the Fern Hollow Bridge in Pittsburgh. The K frame-structure bridge had been placed on a shortened inspection cycle of 12 months vs. 24 due to its poor condition. It was also load-restricted, and in its most recent inspection report, numerous recommendations for repairs and maintenance hadn’t been carried out. Fortunately, no one died when the bridge collapsed under its own weight in the early morning hours of Jan. 28, 2022.

Identifying areas of section loss and corrosion on steel bridges is one of the most important jobs of a bridge inspector. Severe section loss, like what is shown in this picture, can drastically reduce the load-carrying capacity of a bridge.

Spalling and exposed rebar are among the more common defects seen on a concrete bridge. As concrete deteriorates, it can expose a bridge’s reinforcement. As spalling becomes more widespread, structural capacity may be reduced. It is important for an inspector to accurately measure the area of spalling to help determine the extent of needed repairs.

There’s no telling how many lives have been saved by the creation of the NBIS, though we can’t say for certain that the bridge collapse that influenced the NBIS’s creation could have been prevented by a bridge inspection alone. The Silver Bridge, with its nonredundant design, was a ticking time bomb. The cracked eyebar that ultimately brought the structure down was in a location that couldn’t have been seen. Specialized equipment for testing steel and locating cracks had yet to be invented. Therefore, the bridge inspectors of the time wouldn’t have found the defect.

Sliding out to ensure that the bottom flange weld on a floor beam on the Horace Wilkinson Bridge in Baton Rouge is in good condition

National rating standards

As stated earlier, every bridge more than 20 ft long on the National Highway System must be inspected every two years. So must bridges of shorter length if specified by the state. Together, they make up the National Bridge Inventory.

Spalling and exposed rebar are among the more common defects seen on concrete bridges. As concrete deteriorates, it can expose the bridge’s reinforcement. As spalling becomes more widespread, structural capacity may be reduced. It’s important for an inspector to accurately measure the area of spalling to help determine the extent of needed repairs.

As deterioration advances and the condition of a bridge worsens, it may be necessary to inspect the bridge at 12- or six-month intervals. As each bridge is inspected and its condition inventoried, the results and corresponding report are used by state and federal agencies to allocate funding. Inspections are important, not just for keeping drivers and pedestrians safe but also for ensuring that taxpayer dollars are spent efficiently and effectively.

The snooper is the most common way to inspect a bridge superstructure when lane closures are permitted.

The nationwide inspection standards ensure that even small rural bridges aren’t neglected. These types of bridges make up the majority of structures in the National Bridge Inventory system. Of the thousands of structurally deficient bridges across the country, the vast majority are of the single-span variety. Although the smaller bridges don’t command the attention of their bigger, more traveled counterparts, the smaller bridges are still an integral part of the nation’s transportation infrastructure and contribute to the overall movement of people and goods.

Bridge inspections are broken down into components (deck, superstructure, substructure and culvert) and elements (more specific items, such as steel beams, guardrail, signage, bearings, and abutments). The element-level items feed into the component ratings, which govern the overall bridge rating. The overall bridge rating is controlled by the lowest component-level rating and is given in tiers of Good, Fair, Poor, and Critical. Components are rated on a scale of 0 to 9, where a rating of 9 is excellent condition without a single defect, and a rating of 0 is a failed bridge that must be taken out of service.

Ratings of 7 to 9 are considered “Good,” 5 and 6 are considered “Fair,” 3 and 4 are “Poor,” and anything 2 or below is “Critical.” Condition ratings are based on the level of deterioration and potential impact on the structure’s load-carrying ability. Advanced section loss, cracking, spalling, unexpected movement, or deflection all contribute to a bridge receiving a Poor or Critical rating. These standards are national, so ratings mean the same thing in every state; inspectors across the country evaluate bridges consistently regardless of location. What the individual state agencies choose to do after inspection reports are issued is up to them.

The job of a bridge inspector

To become a Certified Bridge Safety Inspector, candidates must take a one- or two-week course, depending on whether they are licensed engineers. Individual states may require additional course work beyond the federal requirements. Additional training is available for inspectors who are interested in inspecting more complex structures like fracture-critical bridges or tunnels. Underwater inspections also require additional course work. Inspectors may become team leaders as their careers progress, and they successfully complete inspections and keep up with their training. Educational requirements vary by state. An engineering degree helps, but it’s not required.

Once the training has been completed, the fun really starts. For smaller bridges, the inspector will work entirely on foot, walking the bridge deck looking for cracking and other signs of stress. It’s normal for a certain level of minor cracking to be present in a bridge deck, but as cracks propagate and become wider or concentrated in a single location, it presents a means for water to corrode the reinforcement or leach the strength from the cement. While working topside, inspectors also inspect all of the bridge’s safety features, like guardrails, for advance warning signs that could indicate a narrow bridge or load posting, and approach roadways for signs of settlement at the abutments. The pavement approaching a bridge isn’t necessarily part of the bridge, but it should be monitored.

Moving under the deck to inspect the beams or girders and substructure units, the inspector will focus on high-stress concentration zones on the beams, specifically looking for cracks and exposed strands in prestressed concrete beam bridges, and cracks, corrosion, and section loss in steel superstructure bridges. Defects in the superstructure will commonly be found at the ends of the beams, where shear is at its highest; in the midspan, where moment is at its highest; or under open joints, where leaking water causes corrosion.

At the substructures, which are typically concrete abutments and piers, inspectors look for cracks, spalling, and signs of settlement. It’s not always easy or possible to inspect the foundation of a bridge—either the footing or deep foundation—but signs of distress in the exposed stem of the substructure can point to what might be happening below ground. For bridges at waterway crossings, inspectors must assess signs of scour and undermining of the substructure footings. As a stream or river flows past an unprotected substructure, its bearing soils can be washed away, leaving a giant scour hole underneath the footing or exposing piles.

While on the job, inspectors carry an array of tools for assessing the condition of bridge elements, such as hammers for sounding concrete to find deterioration, scrapers and brushes for removing corrosion from steel beams, and tape measures and rulers for determining the size of defects. (Additional tools may be carried onto the bridge, but these are the most common.) Inspectors use markers and paint to indicate defects and zones of deterioration. They quantify the size of defects and give locations so future inspectors can locate and monitor them.

It’s the larger, more complex bridges that provide the most challenges—and rewards. It’s to one such bridge in Louisiana that I was delivered after a long ride in the back of a windowless van.

You have to get up close and personal with a large, complex bridge that can’t be inspected on foot. You have a few options. For bridges that cross major bodies of water or highways, the first option is a snooper truck, which lowers a bucket that carries you over the side of the bridge with a telescoping arm. A skilled snooper operator is a wizard with a joystick who can perform a complicated dance to wiggle the bucket between truss members. Above deck, inspectors may use a manlift that can reach as high as 180 ft.

So why was I dangling under the bridge, rather than in a bucket off a snooper truck? It was a matter of convenience—for the motorists on I-10, that is. The truss bridges across the Mississippi carry a tremendous amount of traffic. The traffic in and out of Baton Rouge can be jammed for miles during rush hour. Using a snooper truck and manlift would require lane closures, creating even longer traffic jams and costing thousands of dollars per day for traffic control.

Bridge inspectors receive certification through the Society of Professional Rope Access Technicians (SPRAT). They must use a variety of rope skills. They’ll rig rope systems to climb deck trusses, use beam rollers to slide down stringers suspended in the air, or hang from a tension line to view both faces of deeper floor beams. As you might imagine, rope access work is extremely demanding, physical work.

But I can’t imagine anything more exciting. Here I was hanging from a harness 100 ft above the Mississippi River, then walking on the top chord 300 ft. in the air. Neither was expected after studying bridge engineering—but nothing could be as rewarding and necessary. A bridge isn’t a drawing on a page, a model on a screen, or a sheet of calculations. Inspecting a bridge up close and seeing how it behaves in the wind and the waves brings a wealth of understanding. You don’t get that working in an office.

This article brought to you by your friendly neighborhood bridge inspector, author Joshua Sadlock

First published Nov. 16, 2022, on engineering.com.

About The Author

Joshua Sadlock

Joshua Sadlock has been working as an engineer since 2011 in the transportation sector. He has worked primarily as a bridge designer with experience in steel, pre-stressed concrete, and culvert structures.