(AP) - State transportation officials are replacing a St. Cloud bridge even though engineers believed a repair to strengthen its steel plates would be adequate in the short run, the St. Cloud Times reported on Sunday.
The DeSoto bridge shares the same design as the Minneapolis bridge that fell on Aug. 1, and like other Minnesota bridges it was re-inspected after the collapse.
On Aug. 10, Minnesota Department of Transportation maintenance engineer Dan Anderson wrote to Nancy Daubenberger, a bridge planning engineer, about failing paint, corroding rebar in the St. Cloud bridge deck, and "some expansion problems with the approaches and concrete deck girder spans on either end of the bridge."
But he reported nothing that would warrant immediate closure, according to the Times, which reviewed MnDOT memos, e-mails and reports.
"In conclusion, the question of do we need painting, plating, deck work that is extraordinary at this time? No," Anderson wrote. "Do we need funding to replace the bridge in the next 8-12 years? Yes."
On March 20 the bridge was hastily closed after inspectors found that four of the steel plates that help hold the bridge together had bowed by about a quarter inch. The same gusset plates are blamed in part for the collapse of the Minneapolis bridge.
A few days later, an engineering firm hired by MnDOT to inspect the gusset plates determined that the bowing probably stemmed from a problem with the original design, not any changes to the bridge's load.
The report by Wiss Janney Elstner Associates stated that the distorted plates are likely due to "original fit up issues," such as mismatched pieces of different thicknesses.
Wiss Janney recommended bracing the gusset plates with steel stiffeners. The firm said the gusset plates are adequately sized and have "sufficient strength" to carry current bridge loads, which were about half that of the I-35W bridge before it collapsed.
The distortions "have not compromised the abilities of the affected gusset plates to sustain required design loads," Wiss Janney's report states.
The immediate closing on March 20 was "admittedly in hindsight a very conservative decision," state bridge engineer Dan Dorgan said.
But he noted the decision was made based on the information available at the time, before the Wiss Janney report was issued.
"That depth of analysis we didn't have the afternoon of March 20," Dorgan said.
The four-lane bridge was built in 1957 and carried 31,000 vehicles a day. It was scheduled for replacement in 2015, and MNDOT had been considering accelerating the timetable to 2010 even before the emergency closure. Dorgan said that was a factor in replacing it instead of repairing it.
The new bridge is scheduled to be open to traffic by November 2009.
Mayor Dave Kleis and Dorgan both said the city's push to build a new bridge rather than repair DeSoto was a significant factor in MnDOT's decision to replace it.
"Our insistence was replace the bridge right away," Kleis said. "Because it makes no sense to put any dollars into it and then have it disrupted for as long as it would be, and then have it disrupted again in 2010."
Information from: St. Cloud Times
(Copyright 2008 by The Associated Press. All Rights Reserved.)