On Aug 4, 3:01 pm, "N:dlzc D:aol T:com \(dlzc\)" wrote: ...
An article in todays Minneapolis Star/Tribune newspaper has some disconcerting information about previous inspection reports.State bridge inspectors warned for nearly a decade before its collapse that the Interstate 35W bridge had "severe" and "extensive" corrosion of its beams and trusses, "widespread cracking" in spans and missing or broken bolts.
Not only was the superstructure in poor condition, but certain components were "beyond tolerable limits," and one of the bridge's piers had "tilted to the north," they reported.
By 2000, the inspectors wrote that "eventual replacement of the entire structure would be preferable" to redecking the bridge. They added: "If bridge replacement is significantly delayed, the bridge should be re-decked."
That recommendation was repeated in every report afterward, but it never happened.
Since the collapse, public attention has focused on consultant reports in 2006 and 2007 that expressed serious reservations about the bridge. But a Star Tribune review of older reports by state inspectors shows that their concerns had been growing since the mid-'90s. ... However, in every report since 2000, inspectors urged the state to replace bolts in a specific area of the bridge, a job listed each year under "Immediate Maintenance Recommendations." .... "The fatigue cracks in the approach spans that occurred in the late1990s were addressed by repairs and retrofitting of connections," MnDOT spokesman Kevin Gutknecht said in a written statement. He added that early replacement of the bridge was not considered in part because "no fatigue cracks had occurred in the main truss spans." ... In 1996, reports took on an urgent tone In many cases the reports simply lay out a long list of problems found rather than rating their severity, but in 1996 the inspectors began to take an urgent tone. Noting that a pier supporting steel spans had tilted to the north, the inspectors warned then, "As this will not be repaired in the near future, this area should be closely inspected!"
In 1998, inspectors wrote that "numerous fatigue cracks were found" in the approach spans on the north and south sides of the bridge, which was then three decades old. The report said the cracks were drilled out and the fractured beams reinforced with bolted plates. ... The 1999 report said those cracks were among "areas of major concern," adding that "due to the widespread cracking these areas will now be inspected on six-month intervals."
Later reports recommended only annual inspections. Gutknecht said no further cracking was reported after November 2000, so the monitoring cycle was increased. ... The university's research concluded in 2001 that "fatigue cracking of the deck truss is not likely",...."As a result, MnDOT does not need to prematurely replace this bridge because of fatigue cracking, avoiding the high cost associated with such a large project." ... But MnDOT inspectors continued to express concern about fatigue cracking after the university report and the department asked the engineering design consultant URS to review the bridge's condition.
URS in 2006 expressed concerns that a serious fatigue crack might go undetected because of the difficulty in inspecting parts of the bridge that were difficult to reach. URS recommended steel plating as a fix.
But MnDOT engineers asked URS to come up with other options and the department ultimately chose an alternative that called for increased inspections and repairing any problems found. URS called that option the "most cost efficient," but warned that "the critical issue of this approach is to ensure" that inspectors don't miss any measurable flaws.
Chief bridge engineer Dan Dorgan said previously that MnDOT chose the inspection option because it worried that drilling to add plates might weaken the bridge.