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Something to think about the next time you drive across a bridge

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Just because a bridge is said to be structurally sound doesn’t mean it won’t fall down, as we see HERE:

Thousands of bridges around the U.S. may be one freak accident or mistake away from collapse, even if the spans are deemed structurally sound.

The crossings are kept standing by engineering design, not supported with brute strength or redundant protections like their more modern counterparts. Bridge regulators call the more risky spans “fracture critical,” meaning that if a single, vital component of the bridge is compromised, it can crumple.

Those vulnerable crossing carry millions of drivers every day. In Boston, a six-lane highway 1A near Logan airport includes a “fracture critical” bridge over Bennington Street. In northern Chicago, an I-90 pass that goes over Ashland Avenue is in the same category. An I-880 bridge over 5th Avenue in Oakland, Calif., is also on the list.

Also in that category is the Interstate 5 bridge over the Skagit River north of Seattle, which collapsed into the water days ago [see photo above] after officials say an oversized truck load clipped the steel truss.

Public officials have focused in recent years on the desperate need for money to repair thousands of bridges deemed structurally deficient, which typically means a major portion of the bridge is in poor condition or worse. But the bridge that collapsed Thursday is not in that deficient category, highlighting another major problem with the nation’s infrastructure: Although it’s rare, some bridges deemed to be fine structurally can still be crippled if they are struck hard enough in the wrong spot…

The most famous failure of a fracture critical bridge was the collapse of the I-35W bridge in Minneapolis during rush hour on Aug. 1, 2007, killing 13 people and injuring more than 100 others. The National Transportation Safety Board concluded that the cause of the collapse was an error by the bridge’s designers — a gusset plate, a key component of the bridge, was too thin. The plate was only half of the required one-inch thickness.

Because the bridge’s key structures lacked redundancy, where if one piece fails, there is another piece to prevent the bridge from falling, when the gusset plate broke, much of the bridge collapsed…

About 18,000 fracture critical bridges were built from the mid-1950s through the late 1970s in an effort to complete the nation’s interstate highway system, which was launched under President Dwight Eisenhower, LePatner said in an interview. The fracture critical bridge designs were cheaper than bridges designed with redundancy, he said.

Thousands of those bridges remain in use, according to an AP analysis.

“They have been left hanging with little maintenance for four decades now,” he said. “There is little political will and less political leadership to commit the tens of billions of dollars needed” to fix them…

There is wide recognition at all levels of government that the failure to address aging infrastructure will likely undermine safety and hinder economic growth. But there is no consensus on how to pay for improvements. The federal Highway Trust Fund, which provides construction aid to states, is forecast to go broke next year. The fund gets its revenue primarily from federal gas and diesel taxes. But revenues aren’t keeping up because people are driving less and there are more fuel-efficient cars on the road.

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3 Comments

  1. Steverino

    Every metropolitan area in the US has hundreds of bridges that require repair or replacement. That’s a lot of good construction jobs that can feed the economy for many years.

  2. Robert

    Steverino, from what I’ve read, the long term plan is to privatize the nations bridges, streets and highways and includes the repair of these pathways by the new private owners. In turn they will make them tollways and toll bridges. The usage of streets and highways are going to be charged by the mile driven. Those little nipples on new cars since 2006 are part of that plan. This is also why we’re seeing the return of the bicycle as a main transportation method. Global climate change is also playing a role in this plan.

    There’s a pilot plan, that’s been in place for several years, using taxi’s as the beta test to charge cars by the mile to use the public thoroughfare’s. Thoroughfare’s we tax payers built and paid for with our tax dollars.

    The whole country’s public infrastructure is going to be sold off. That includes schools, water systems, public transportation networks, and eventually, the police forces. Welcome to the utopian world the capitalists have dreamed of for decades. This is also why the inner cities, especially in the larger metro’s are being developed to increase the population density, as people move closer in to be near where the central services will be offered the cheapest.

    This all coincides with the price of energy escalating because the easiest to reach, cheapest to refine and cleanest sweet crude oil to discover, is behind us. This is why we are now seeing more and more deep water wells being dug and why we are seeing the usage of new technologies like fracking/high pressure steaming, which will release reserves that were in prior times not accessible. Between the privatization of civil services and the rising cost of energy, the lifestyle we once knew is going to change dramatically. Fortunately, this change will still take many decades to complete, but none the less noticeable.

    You know how when you go see a play, there’s an usher that hands out a program to give you an overview of what the evenings entertainment will include? Well, there’s a long term plan out there, but we the people never received the program. It’s being dribbled out to us a little bit a time as big change are very difficult for most.

    Just how hard to Obama fight for works programs like we saw under FDR? He didn’t. Paid lip service but that where it stopped. Never did he rally the people to back him for jobs programs. He never even showed up in Wisconsin to back the labor unions. And yet many people on the left think he’s their savior.

  3. Craig Knauss

    Bridges are designed to distribute the loads (vehicles and the bridge) to multiple members (girders) and then transfer the load to reaction points (piers and abutments). Vehicle loads are usually vertical due to gravity, with a little linear loading due to traffic starting and stopping. The bridges are not designed for major transverse impact loading because traffic seldom goes crosswise on the bridges. However, sometimes bridges are hit by ships and barges that are going crosswise. That’s why we would see large pier protection structures made of pilings or caissons placed in front of the piers that are in or adjacent to the navigation channel. This is not done for non-commercial navigation channels since small boats couldn’t cause enough damage to the piers. We could design and build bridges with protection from all conceivable impacts from all conceivable directions, including aircraft, but we can’t afford to build them.

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