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The Brooklyn Bridge
(from USA Today) WASHINGTON (AP) – …An Associated Press analysis of 607,380 bridges in the most recent federal National Bridge Inventory showed that 65,605 were classified as “structurally deficient” and 20,808 as “fracture critical.” Of those, 7,795 were both – a combination of red flags that experts say indicate significant disrepair and similar risk of collapse.
A bridge is deemed fracture critical when it doesn’t have redundant protections and is at risk of collapse if a single, vital component fails. A bridge is structurally deficient when it is in need of rehabilitation or replacement because at least one major component of the span has advanced deterioration or other problems that lead inspectors to deem its condition poor or worse.
Engineers say the bridges are safe. And despite the ominous sounding classifications, officials say that even bridges that are structurally deficient or fracture critical are not about to collapse.
Cracked concrete exposes parts of reinforcement bars on the Frederick Douglass Memorial Bridge which spans the Anacostia River in Washington on Sept. 4, 2013. (Photo: Alex Brandon, AP)
The AP zeroed in on the Frederick Douglass Memorial Bridge into Washington DC and others that fit both criteria – structurally deficient and fracture critical. Together, they carry more than 29 million drivers a day, and many were built more than 60 years ago. Those bridges are located in all 50 states, plus Puerto Rico and the District of Columbia, and include the Brooklyn Bridge in New York, a bridge on the New Jersey highway that leads to the Lincoln Tunnel, and the Main Avenue Bridge in Cleveland.
The number of bridges nationwide that are both structurally deficient and fracture critical has been fairly constant for a number of years, experts say. But both lists fluctuate frequently, especially at the state level, since repairs can move a bridge out of the deficient categories while spans that grow more dilapidated can be put on the lists. There are occasional data-entry errors. There also is considerable lag time between when state transportation officials report data to the federal government and when updates are made to the National Bridge Inventory.
Many fracture critical bridges were erected in the 1950s to 1970s during construction of the interstate highway system because they were relatively cheap and easy to build. Now they have exceeded their designed life expectancy but are still carrying traffic – often more cars and trucks than they were originally expected to handle. The Interstate 5 bridge in Washington state that collapsed in May was fracture critical.
Cities and states would like to replace the aging and vulnerable bridges, but few have the money; nationally, it is a multibillion-dollar problem. As a result, highway engineers are juggling repairs and retrofits in an effort to stay ahead of the deterioration.
There are thousands of inspectors across the country “in the field every day to determine the safety of the nation’s bridges,” Victor Mendez, head of the Federal Highway Administration, said in a statement. “If a bridge is found to be unsafe, immediate action is taken.” At the same time, all that is required to cause a fracture critical bridge to collapse is a single unanticipated event that damages a critical portion of the structure. …
Signs of age are clear. The Douglass bridge into D.C., also known as the South Capitol Street Bridge, was designed to last 50 years. It’s now 13 years past that. The district’s transportation department has inserted so-called catcher beams underneath the bridge’s main horizontal beams to keep the bridge from falling into the river, should a main component fail.
Alesia Tisdall, who drove over the bridge every day for 15 years but now crosses it only occasionally, said she found its “bounce” unnerving. “You’d look at the person sitting next to you like, ‘Did you feel that bounce?’ And they’d be looking back at you like they were thinking the same thing,” said Tisdall…
Peter Vanderzee, CEO of Lifespan Technologies of Alpharetta, Ga., which uses special sensors to monitor bridges for stress, said steel fatigue is a problem in the older bridges.
“Bridges aren’t built to last forever,” he said. He compared steel bridges to a paper clip that’s opened and bent back and forth until it breaks. “That’s a fatigue failure,” he said. “In a bridge system, it may take millions of cycles before it breaks. But many of these bridges have seen millions of cycles of loading and unloading.”
That fatigue is evident in a steel truss bridge over Interstate 5 in Washington state – south of the similar steel truss that collapsed in May. The span that carries northbound drivers over the east fork of the Lewis River was built in 1936.
Because of age, corrosion and metal fatigue caused by vibration, the state has implemented weight restrictions on the bridge. Washington state Department of Transportation spokeswoman Heidi Sause said the bridge wasn’t built for the kind of wear – bigger loads and more traffic – that is now common. “This is a bridge that we pay close attention to and we monitor very carefully,” Sause said.
….
There are wide gaps between states in historical bridge construction and their ongoing maintenance. While the numbers at the state level are in flux, Iowa, Nebraska, Missouri and Pennsylvania have all been listed recently in the national inventory as having more than 600 bridges both structurally deficient and fracture critical.
….
Officials say northeastern states face particular challenges because the infrastructure there is older and the weather is more grueling, with dramatic and frequent freeze-thaw cycles that can put stress on roads and bridges.
Many Pennsylvania lawmakers have long sought to boost transportation funding, in part to address crumbling bridges. But this year’s proposals, including Gov. Tom Corbett’s $1.8 billion plan, stalled amid fights over details.
That’s a common issue among infrastructure managers in other states, who say they don’t have the money to replace all the bridges that need work. Instead, they continue to do patch fixes and temporary improvements.
…..
Congressional interest in fixing bridges rose after the 2007 collapse in Minneapolis, but efforts to add billions of extra federal dollars specifically for repair and replacement of deficient and obsolete bridges foundered. A sweeping transportation law enacted last year eliminated a dedicated bridge fund that had been around for more than three decades. State transportation officials had complained the fund’s requirements were too restrictive. Now, bridge repairs or replacements must compete with other types of highway projects for federal aid.
The new law requires states to beef up bridge inspection standards and qualifications for bridge inspectors. However, federal regulators are still drafting the new standards.
“Do we have the funding to replace 18,000 fracture critical bridges right now?” Kelley Rehm, bridges program manager for the American Association of State Highway and Transportation Officials asked. “No. Would we like to? Of course.”
From the Associated Press. Reprinted here for educational purposes only. May not be reproduced on other websites without permission from USA Today. Visit the website at USAToday.com.
Questions
1. a) What is the National Bridge Inventory? (see “Background” below the questions for the answer)
b) How many U.S. bridges were inspected for the NBI report?
c) How does the FHWA determine which bridges to inspect for its NBI report? (see “Background” below the questions for the answer)
d) How many bridges were classified structurally deficient; how many were classified fracture critical; how many were classified as both structurally deficient and fracture critical?
2. Define structurally deficient and fracture critical.
3. Define vital component and redundant protections as used in para. 2.
4. a) How do engineers and officials view bridges that are structurally deficient or fracture critical?
b) What reassurance does the head of the FHA, Victor Mendez, give for concerns about bridge safety?
5. List the reasons that many bridges need to be repaired or replaced.
6. What is the main reason many bridges are not getting needed repairs, and instead getting patches or temporary improvements?
7. a) What do you think: The federal government gets its money from the states (income tax, corporate tax and other taxes). If the federal government does not have the money to give states the funding needed to repair bridges, should the money be taken from other government programs (education, military, medicaid/medicare, etc.) to do so? Or should taxes be raised to get the money needed? If so, which taxes? Or should the states find money to fix their bridges? Or are the repairs being made now adequate? Explain your answer.
b) Ask a parent the same question.
Background
The Federal Highway Administration (FHWA) is an agency within the U.S. Department of Transportation that supports State and local governments in the design, construction, and maintenance of the Nation’s highway system (Federal Aid Highway Program) …
Through financial and technical assistance to State and local governments, the Federal Highway Administration is responsible for ensuring that America’s roads and highways continue to be among the safest and most technologically sound in the world. (From the FHWA website: fhwa.dot.gov/about
For the FHWA National Bridge Inventory page, go to: fhwa.dot.gov/bridge/nbi.cfm.
The National Bridge Inventory:
- The National Bridge Inventory (NBI) is a database, compiled by the Federal Highway Administration, with information on all bridges and tunnels in the U.S. that have roads passing above or below.
- This bridge information includes the design of the bridge and the dimensions of the usable portion. The data is often used to analyze bridges and judge their conditions.
- The bridge inventory is developed with the purpose of having a unified database for bridges, including identification information, bridge types and specifications, operational conditions, bridge data including geometric data and functional description, inspection data, etc.
- Any bridge more than 20 feet long used for vehicular traffic is included.
The NBI is used for federal funding purposes. A “bridge sufficiency rating” is calculated, based 55% on the structural evaluation, 30% on the obsolescence of its design, and 15% on its importance to the public. As of 2008, a score of 80 or less is required for federal repair funding, and 50 or less for federal replacement funding.
- The NBI also classifies bridges as either “structurally deficient” or “functionally obsolete.” Neither necessarily implies lack of safety, though that could be a concern as well.
- “Structurally deficient” means that the condition of the bridge includes a significant defect, which often means that speed or weight limits must be put on the bridge to ensure safety; a structural evaluation of 4 or lower qualifies a bridge as “structurally deficient.” The designation can also apply if the approaches flood regularly.
- “Functionally obsolete” means that the design of a bridge is not suitable for its current use, such as lack of safety shoulders or the inability to handle current traffic volume, speed, size, or weight.
- In December 2008, 72,868 bridges in the United States (12.1%) were categorized as “structurally deficient,” representing an estimated $48 billion in repairs, and 89,024 (12.2%) were rated “functionally obsolete,” representing an estimated $91 billion in replacement costs.
- Some bridges are also identified as “fracture critical“, which means that (usually due to low-cost design) the failure of any one main structural member will cause a significant portion or the entire bridge to collapse. Such designs were discontinued in the 1970s. Fracture critical designs can leave bridges vulnerable to collisions with ships or large trucks, as in the I-5 Skagit River Bridge collapse.
The NBI was subjected to scrutiny and questions, after new actions revealed it might be outdated or inaccurate. Federal officials attempted to order emergency inspections of all steel truss bridges after a major bridge collapse in Minneapolis in 2007. However, it was found that many records within the NBI were inaccurate or out of date. (from wikipedia)
From the USA Today article:
The biggest difference between the bridge over the Lewis River and the one over the Skagit River that collapsed May 23 is that the span still standing has actually been listed in worse condition. State officials hope to replace it in the next 10 to 15 years.
While the Skagit span was not structurally deficient, the I-35W bridge that collapsed in Minneapolis in 2007 had received that designation. The bridge fell during rush hour, killing 13 people and injuring more than 100. The National Transportation Safety Board concluded that the cause of the collapse was an error by the bridge’s designers, not the deficiencies found by inspectors. A gusset plate, a fracture critical component of the bridge, was too thin.
Many of the bridges included in the AP review have sufficiency ratings — a score designed to gauge the importance of replacing the span — that are much lower than the Skagit bridge. A bridge with a score less than 50 on a 100-point scale can be eligible for federal funds to help replace the span. More than 400 bridges that are fracture critical and structurally deficient have a score of less than 10, according to the latest federal inventory.
The Brooklyn Bridge is among the worst.
Pennsylvania has whittled down its backlog of structurally deficient bridges but still has many more to go, with an estimated 300 bridges in position to move onto the structurally deficient list every year if no maintenance is done. Barry Schoch, the state transportation secretary, said in an interview that officials would like to add redundancy to fracture critical bridges when they can, particularly if a bridge is also structurally deficient.
“Those are high on the priority list,” Schoch said.
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