- Asset Management
- Solutions or Hardware?
- Key Project Summaries
- Bridge Preservation
- White Papers
- Contact Us
White Paper #1
Why We Just Can’t Spend Our Way to Safer Bridges
A White Paper by LifeSpan Technologies
Since August 1st, the public has been bombarded with the term, “structurally deficient”. And the TV images of the Minneapolis I-35W bridge collapse keep reminding us about the next bridge we drive over. Is it structurally deficient? Should I take a detour? Who’s looking out for my family?
LifeSpan would like to examine this complex issue and suggest how we, as citizens and transportation users, can more confidently use and most efficiently improve our transportation network. And without feeling stressed every time we cross a bridge, or bankrupt our country in a politically-correct frenzy to throw money at the problem.
First, let’s explore how we arrived at this state of affairs.
In 1967, the Silver Bridge collapse over the Ohio River resulted in a programmatic response from Congress and the Federal Highway Administration (FHWA) (1) to institute a biennial bridge inspection program called the National Bridge Inspection Standards, or NBIS. Inspectors were hired by State Departments of Transportation (DOTs), training courses were implemented, and the inspection process began in earnest.
In the main, inspectors are technically oriented, but they are generally not professional engineers. For over thirty years, inspectors have used their eyes, flashlights, ball-peen hammers, wire brushes, rulers, cameras and clipboards to assess the condition of every bridge in their state over twenty feet long. Recently, more inspection work has been subcontracted to third parties to meet the need as large numbers of retirements have hit the DOTs. Inspectors have done a reasonably good job over time, but many of America’s bridges are reaching the end of their design life, are being crossed by overweight vehicles, and have not received adequate maintenance in a long time.
Over the past several years, thought leaders in the transportation industry have been questioning the effectiveness of visual inspection using the NBIS protocols. In a 2001 landmark study, Reliability of Visual Bridge Inspection (2), the FHWA concluded that visual inspection is subjective, highly variable, and non-repeatable.
In response to this problem, the FHWA proposed the Long Term Bridge Performance Program (LTBPP), twenty years in duration. The purpose of the LTBPP is to demonstrate better condition assessment technologies and analytical methods that can accurately determine the health of a bridge structure – in near real time. But, as much promise as this program has for a long-term solution, we have to address our short term crisis right now.
The National Bridge Inventory (NBI), basically a database used by the FHWA for analytical purposes, currently classifies about 150,000 total bridges (out of a total 590,000 bridges) as structurally deficient or functionally obsolete. There is a big difference between these two classifications. Functionally obsolete means the bridge is not current with today’s design standards or cannot handle the necessary traffic demands. Importantly, this classification does not mean the bridge is unsafe to use. On the other hand, the classification of structurally deficient means there are problems that have been found which diminish the structural integrity of the bridge. It doesn’t mean the bridge is about to fail – rather, it tells owners that the bridge should be “posted”, (allowable loads restricted), repaired or replaced; and probably inspected more frequently. In hindsight, the term “structurally deficient” was probably a bad choice of words, especially when trying to explain this term to the press and public.
Bridges are complex structures and, consequently, are designed and constructed with what are called Factors of Safety (FOS). To explain FOS in simple terms; if a bridge needs to routinely carry 50,000 pounds safely, the final design may be capable of actually carrying 150,000 pounds upon completion of construction. This is good engineering practice and is widely used for bridges, buildings, dams and other civil structures. Because we can’t know today what the future loading or deterioration rate may be, engineers purposely over-design (use an FOS) to create a safety cushion to meet tomorrow’s demands.
The American Association of State Highway Transportation Officials (AASHTO) (3), a quasi-government organization, is responsible for developing and setting design standards for bridges. AASHTO is to be commended for its success over many decades in making sure American bridges are well designed and have a long, useful life. However, AASHTO can’t stop the aging process and that is what is causing so much angst among bridge owners, the FHWA, and American citizens that use the transportation infrastructure.
Defining the Challenge
The American Society of Civil Engineers (ASCE) (4) a private organization, publishes a Report Card on America’s Infrastructure (5) every two years. The last publication was 2005 and bridges received a grade of C, not bad when compared to dams, wastewater treatment and schools, which all received a D grade. The ASCE estimates a total cost of $1.6 TRILLION dollars to correct our infrastructure deficiencies. That’s over six times greater than what the last Transportation Bill allotted for a six year period, almost triple what we’ve spent in Iraq, or over $5,000 for every man, woman and child in America – a very scary total.
Bottom line: Our infrastructure won’t all get fixed and certainly not quickly.
Where are your Federal tax dollars going instead of fixing bridges? Over 80% of the Federal budget is for non-discretionary spending – debt interest, social entitlements, and defense (6). And, we are still in the red every year, spending more than we take in.
Bottom line: Even meaningful funding to repair all structurally deficient bridges won’t be available for the foreseeable future. We just don’t have that much discretionary funding.
Something changed in the later part of the 20th century that caused America’s infrastructure to slip from first class to third class. Those who travel in Europe or Asia experience well maintained and smooth roads, bridges without weight limits, and generally less congestion (big cities are exceptions of course!). Why have we let this happen? The answer is easy – MONEY. With ever more pressing needs for Federal funding, including. Social Security, Medicare, national debt interest, and the other programs that are important; we’ve taken our eye off the proverbial ball.
State DOTs, who are tethered to the Federal spigot, have done the best they can with limited funding. State DOTs start every morning with the intent of making the best decisions regarding maintenance, inspection, evaluation, repair, and replacement; or building new capacity. But all too often, DOTs have their priorities changed by political demands from the state legislative and executive branches. New spotlights better than repair.
In an odd twist of fate, the state DOTs have been hampered by the NBIS visual inspection protocol.
If the visual inspection of a bridge and the subsequent analytical work indicates that a bridge is structurally deficient, i.e. it received an overall sufficiency rating of four or less, in the real world the bridge might be a two or a six. The subjectivity and variability in visual inspection, coupled with highly conservative analytic protocols, could make all the difference in how that bridge is managed in the future. If engineers knew the bridge was actually a six, they could safely defer planned repair or replacement projects without concern for public safety. Conversely, if engineers knew the bridge was really a two, they might take significant, immediate action to repair, restrict weight, or even close the bridge.
The point is this — the inherent variability and subjectivity in the visual condition assessment protocol, as stated in the 2001 FHWA report, make optimized bridge management more difficult and may result in either work that doesn’t need to be done, or work delayed that definitely needs to be done.
Here’s an example. One of LifeSpan’s clients received a third party bridge visual inspection report that noted some corrosion on the steel truss members and recommended a refurbishment program that would cost almost $1 million dollars. Before the repair work was started, LifeSpan installed a structural health monitoring system and captured key strain and temperature data for approximately six months. After the data was captured, a major U.S. engineering firm developed a mathematical model (finite element model) of the structure and used the captured LifeSpan bridge data to calibrate the model.
The engineering firm recommended safe deferral of the repair program, but also noted another problem that was not addressed in the visual inspection report. This problem, typical with old bridges, would not allow stresses from large temperature differentials to redistribute or be attenuated; rather it concentrated those forces, which is not desirable for long-term bridge operation.
So in this example, LifeSpan was able to demonstrate to our client how to save nearly $1 million dollars, but also pinpointed another problem that wasn’t noted on the visual inspection report. Further, our client now has a calibrated mathematical model that can be used to plan future inspections, which will focus the inspections on high stress areas shown on the finite element model, and generally make the next inspection cycle more productive.
The challenge bridge owners face is twofold. First, they don’t really have sufficiently precise knowledge about the condition of their bridge infrastructure. This is the result of an inspection process that is subjective and highly variable. And second, they don’t expect to have sufficient funding to address all the perceived needs, so compromise is absolutely essential.
But where and how do we all start compromising when we can’t precisely define the problem?
The Reasoned Path Forward
About 150,000 bridges across the U.S. in the National Bridge Inventory are either structurally deficient (70,000 +/-) or functionally obsolete (80,000 +/-) (7). So …
- Should we address the deficient or obsolete bridges first?
- And, in what order?
- And, when can we add new capacity to relieve congestion?
- And, the most important question, how are we going to afford all this?
Here’s the rub: To really upgrade our transportation network, we need to correct the deficiencies, replace obsolete structures, AND add new capacity to cut down on congestion. That probably means the U.S. has need for up to 200,000 separate bridge actions; repair, replace, or new. The ASCE estimates nearly $200 billion over 20 years.
Simple conclusion: It won’t happen in our lifetime.
A functionally obsolete bridge is still safe to use, so its replacement can be delayed without jeopardizing the public safety. However, a structurally deficient bridge must be considered a candidate for repair or replacement at some future date. The truly important issue we must face is how we can make definitive, objective plans to defer, repair, or replace our nation’s deficient bridges, while adding sorely needed new capacity.
It won’t be easy.
The real answer to this challenge originates in capturing and using better information.
The structure owners simply must receive more precise, objective information about the condition of their bridges before they start allocating billions of dollars to replace them. LifeSpan and other firms are discovering that bridges, especially short span bridges, typically have load carrying capacity higher than visual inspection might indicate. In many cases, this single fact allows owners to defer repair or replacement actions on bridges determined to be in better condition and concentrate those monies on bridges that rate immediate attention. It’s all about better decisions that are supported by better information.
When the NBIS program was initiated, highly accurate sensors, wireless communication and the Internet were not available. Today, the product of these enabling technologies, called structural health monitoring systems, makes it possible to capture highly accurate data on a 7×24 basis that can be used to determine the health of a structurally deficient bridge. In addition, monitoring systems can provide alerts to bridge managers if some captured bridge data is out of tolerance – the equivalent of what you might experience if you have a home burglar and fire alarm coupled to a central monitoring facility.
In the aftermath of the Minneapolis I-35W bridge collapse, the FHWA directed state DOTs to re-inspect all 750+ deck truss bridges of similar design. Using the same old visual inspection techniques, why should we expect different results this time? And given this tragic experience, one has to wonder why America continues to rely solely on an inspection protocol which the FHWA acknowledges has significant limitations.
Our suggestion is to rapidly implement commercially available structural health monitoring technologies for bridges that are classified as structurally deficient. Start with the most deficient. Yes, it will mean that some other government program will be delayed. But considering the cost of failures, both in human and capital terms, why should we avoid adopting better technology? Given the events of last week, we think most would agree that structural monitoring technology should be considered state-of-the-art and perhaps the standard of care for the engineering community.
Consider this — if all 750+ steel deck truss bridges in the U.S. just ordered re-inspected by the FHWA had structural monitoring systems installed tomorrow, the total cost of all installed systems would be less than half the funding that was allocated for the Bridge to Nowhere in Alaska several years ago.
Also, don’t be surprised if your county can’t get liability insurance coverage or pays sky-high premiums next year for the structurally deficient bridges that they own.
Conclusions and Final Comments
Industry and owner experience with structural health monitoring shows that a significant percentage of bridges are in better condition than visual inspection indicates. Therefore, bridge owners can win two ways by adopting structural health monitoring technology:
- Bridges in better condition could have planned repair or replacement programs deferred or weight limitations removed.
- Bridges in worse condition could have weight limitations imposed or lowered; repair programs accelerated, and, most importantly, improved margins of safety for the public.
Perhaps someday soon, public officials will be just as happy having their picture taken standing under an older monitored bridge as they do cutting the ribbon for a new bridge. LifeSpan will even be happy to provide the sign — $50 million of your tax dollars were saved by safely extending the life of this structurally sound bridge.
And finally, we have great sympathy for those families who lost loved ones as a result of the I-35W bridge collapse. This tragic, watershed event in Minneapolis gives elected officials and bridge owners a powerful mandate to adopt better condition assessment technologies – and fast. After all, it’s about being responsible and responsive to the American taxpayers, who write the checks on April 15th.
6. http://www.gpoaccess.gov/usbudget/ and a pie chart at
For more information, contact LifeSpan Technologies on the Web at www.lifespantechnologies.com,
or by calling 770-234-9494.