Our dear Saraight bridge is also nearing it's designed life. Someday it may also collapse and snap the communications. There is talk of building another 4-lane bridge alongside. When this will come up is a matter of guess.
-manoj On 8/9/07, Dilip/Dil Deka <[EMAIL PROTECTED]> wrote: > > If you have been following the Minnesota bridge collapse, you may find the > following article interesting. These are speculations right now. But I > suspect they are based on the shape of the steel debris. The extra weight > due to maintenance equipment and material could have resulted in > concentrated loading on some of the gusset plates. It is a standard practice > in USA to keep some lanes open on roads and bridges during repair. The > combined loading may not have been taken into consideration by those who let > out the contract to repair. > > In the refinery and chemicals business, it is a standard practice to look > at both operations and maintenace while designing the plants. > Dilip Deka > ================================================================ > > *Potential Flaw Seen in Design of Fallen Bridge* > By MONICA > DAVEY<http://topics.nytimes.com/top/reference/timestopics/people/d/monica_davey/index.html?inline=nyt-per>and > MATTHEW > L. > WALD<http://topics.nytimes.com/top/reference/timestopics/people/w/matthew_l_wald/index.html?inline=nyt-per> > Published: August 9, 2007 > MINNEAPOLIS, Aug. 8 — Investigators have found what may be a design flaw > in the bridge that collapsed here a week ago, in the steel parts that > connect girders, raising safety concerns for other bridges around the > country, federal officials said on Wednesday. > > <http://topics.nytimes.com/top/reference/timestopics/subjects/b/bridges_and_tunnels/bridge_disasters/index.html> > > Ruth Fremson/The New York Times > Work continued on Wednesday in removing wreckage from the collapsed > Minneapolis bridge. > The Federal Highway Administration swiftly responded by urging all states > to take extra care with how much weight they place on bridges of any design > when sending construction crews to work on them. Crews were doing work on > the deck of the Interstate 35W bridge here when it gave way, hurling > rush-hour traffic into the Mississippi River and killing at least five > people. > The National Transportation Safety > Board<http://topics.nytimes.com/top/reference/timestopics/organizations/n/national_transportation_safety_board/index.html?inline=nyt-org>'s > investigation is months from completion, and officials in Washington said > they were still working to confirm the design flaw in the so-called gusset > plates and what, if any, role they had in the collapse. > Still, in making public their suspicion about a flaw, the investigators > were signaling they considered it a potentially crucial discovery and also a > safety concern for other bridges. Gusset plates are used in the construction > of many bridges, not just those with a similar design to the one here. > "Given the questions being raised by the N.T.S.B., it is vital that states > remain mindful of the extra weight construction projects place on bridges," > Secretary of Transportation Mary E. Peters said in a statement issued late > Wednesday. > Since the collapse, the concern among investigators has focused on > "fracture critical" bridges, which can collapse if even a single part fails. > But neither the safety board nor the federal Department of Transportation on > Wednesday singled out any particular design of bridge in raising its new > concerns about gusset plates and the weight of construction equipment. > Concerns about the plates emerged not from the waters of the Mississippi > River here, where workers have only begun to remove cars and the wreckage > with cranes, but from scrutiny of the vast design records related to the > steel truss bridge. > In Minneapolis, state transportation department officials seemed surprised > by the sudden focus on the bridge's gusset plates, which are the steel > connectors used to hold together the girders on the truss of a bridge. On > this bridge, completed in 1967, there would have been hundreds of them, > officials here said. > Gary Peterson, the state's assistant bridge engineer, said he knew of no > questions that had ever been raised about the gusset plates, no unique > qualities to distinguish them from those on other bridges, no inkling of any > problem during decades of inspections of the bridge. > "I don't know what this could be," Mr. Peterson said. "I'm frankly > surprised at this point. I can't even begin to speculate." > If those who designed the bridge in 1964 miscalculated the loads and used > metal parts that were too weak for the job, it would recast the national > debate that has emerged since the collapse a week ago, about whether enough > attention has been paid to maintenance, and raises the possibility that the > bridge was structurally deficient from the day it opened. It does not > explain, however, why the bridge stood for 40 years before collapsing. > In an announcement, the safety board said its investigators were > "verifying the loads and stresses" on the plates as well as checking what > they were made of and how strong they were. > State authorities here said the plates were made of steel, and were, in > most such bridges, shaped like squares, five feet by five feet, and a half > inch thick. Such plates are common in bridges as a way to attach several > girders together, said Jan Achenbach, an expert in testing metals at the > Northwestern > University<http://topics.nytimes.com/top/reference/timestopics/organizations/n/northwestern_university/index.html?inline=nyt-org>Center > for Quality Engineering and Failure Prevention. > A consultant hired by the State of Minnesota in the days after the > collapse to conduct an investigation of what had gone wrong, even as the > national safety board did its work, first discovered the potential flaw, the > board said. Representatives at Wiss, Janney, Elstner Associates Inc., the > consulting firm, could not be reached late Wednesday. > *Federal authorities said one added stress on the gusset plates may have > been the weight of construction equipment and nearly 100 tons of gravel on > the bridge, where maintenance work was proceeding when the collapse > occurred. A construction crew had removed part of the deck with 45-pound > jackhammers, in preparation for replacing the two-inch top layer, and that > may also have altered the stresses on the bridge, some experts said.* > The chairman of the National Transportation Safety Board, Mark V. > Rosenker, said on Sunday that investigators were calculating the stresses > generated on each girder and other bridge components from the construction > equipment and materials. > While cautioning states on Wednesday about the weight of construction > equipment and materials, the federal transportation department did not > immediately issue any broader warnings about gusset plates. Brian Turmail, a > spokesman for the Transportation Department, said on Wednesday evening that > his agency was "conducting additional analysis to determine whether we need > to ask the states to do checks of their designs." > If there was a design error in the 1960s, failure to identify it before > the bridge > collapse<http://topics.nytimes.com/top/reference/timestopics/subjects/b/bridges_and_tunnels/bridge_disasters/index.html?inline=nyt-classifier>indicates > a problem with the federal inspection program, said Thomas M. > Downs, who was the associate administrator of the Federal Highway > Administration from 1978 to 1980. > Here, state officials were racing to respond to the new concerns about a > design flaw, but said they had no details. "We're going to leave that to the > N.T.S.B.," said Bob McFarlin, assistant to the commissioner of the > Minnesota<http://topics.nytimes.com/top/news/national/usstatesterritoriesandpossessions/minnesota/index.html?inline=nyt-geo>Department > of Transportation. > Of a potential design flaw, Brian McClung, the spokesman for Gov. Tim > Pawlenty, said the state's transportation department "will be looking into > every single issue and possibility raised by the N.T.S.B. or the parallel > investigation ordered by Governor Pawlenty, including this one." > Mr. Peterson said that concerns about gusset plates might normally focus > on questions of corrosion over time, but that he had never heard of a > question over the original design or metal make up of a plate here. Had > ultrasonic testing of the plates shown signs of corrosion or cracking, that > would be a concern, he said. But in the case of the I-35W bridge, Mr. > Peterson said he recalled "no gusset plate issues at all." > When the bridge was built, in the 1960s, its hundreds of gusset plates > were attached with rivets, though bridge designers here switched to bolts, a > stronger option, in the 1970s. > "Bolts are better," Mr. Peterson said, "but we wouldn't consider anything > wrong with rivets." > Monica Davey reported from Minneapolis, and Matthew L. Wald from > Washington. > > _______________________________________________ > assam mailing list > [email protected] > http://assamnet.org/mailman/listinfo/assam_assamnet.org > >
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