你这种反华份子只看到中国的桥梁坍塌，却对美国的桥梁坍塌视若无睹，简直是标准的美狗。
将来你的美国爹地有桥梁倒塌，记得也做记录，然后也顺便打你自己的脸。
Thousands of U.S. bridges vulnerable to collapse
SEATTLE 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.
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. "It probably is a bit of a fluke in that sense," said Charles Roeder, a professor of civil and environmental engineering at the University of Washington. While the I-5 truck's cargo suffered only minimal damage, it left chaos in its wake, with two vehicles catapulting off the edge of the broken bridge into the river below. Three people involved escaped with non-life threatening injuries. Last August, Barry LePatner, author of "Too Big to Fall: America's Failing Infrastructure and the Way Forward," told CBS News correspondent Jeff Glor on "CBS This Morning" that the next bridge disaster was much closer than anyone wants to believe. "Since 1989," LePatner said, "we've had nearly 600 bridge failures in this country and, while they're not widely publicized ... a large number of bridges in every state are really a danger to the traveling public." 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. Mark Rosenker, who was chairman of the NTSB during the I-35W bridge investigation, said the board looked into whether other fracture critical bridges were collapsing. They found a few cases, but not many, he said. "Today, they're still building fracture critical bridges with the belief that they're not going break," Rosenker said. Fracture critical bridges, like the I-5 span in Washington, are the result of Congress trying to cut corners to save money rather than a lack of engineering know-how, said Barry B. LePatner, a New York real estate attorney and author of "Too Big to Fall: America's Failing Infrastructure and the Way Forward." 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. Along with being at risk of a fatal impact, the I-5 bridge was deemed to be "functionally obsolete," which essentially means it wasn't built to today's standards. Its shoulders were narrow, and it had low clearance. There are 66,749 structurally deficient bridges and 84,748 functionally obsolete bridges in the U.S., including Puerto Rico, according to the Federal Highway Administration. That's about a quarter of the 607,000 total bridges nationally. States and cities have been whittling down that backlog, but slowly. In 2002, about 30 percent of bridges fell into one of those two categories. Spending by states and local government on bridge construction adjusted for inflation has more than doubled since 1998, from $12.3 billion to $28.5 billion last year, according to the American Road and Transportation Builders Association. That's an all-time high. "The needs are so great that even with the growth we've had in the investment level, it's barely moving the needle in terms of moving bridges off these lists," said Alison Premo Black, the association's chief economist. http://www.cbsnews.com/news/thousands-of-us-bridges-vulnerable-to-collapse/
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发表于 15-7-2017 09:04 PM
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