MnDOT has released its previously suppressed 2007 inspection report on the Hastings Bridge, and it shows that the bridge needs immediate attention because of continued deterioration.
An increasing number of crucial bearings that support the bridge are tipped, bolts and plates are missing, and corrosion is so extensive that inspectors told the Minnesota Department of Transportation in August to reevaluate how much tonnage the bridge can support.
The inspection report on the state's busiest two-lane trunk highway bridge also said that the last time MnDOT conducted a load rating was eight years ago, and that a review was immediately necessary to "account for advanced section loss" -- that is, thinning of steel in the bridge's vertical beams and floor.
MnDOT said Monday that the existing 40-ton load limit remains appropriate and is not "controlled" by the corrosion. MnDOT said it is monitoring the bridge and other repairs will be made beginning in April.
As recently as mid-December, the agency had refused to release the August report.
It cited homeland security concerns, saying that criminals or terrorists could use the information to "determine the most vulnerable components of a bridge to target for attack by explosives or other means."
MnDOT didn't explain why it decided to release the information now. The inspectors wrote a 400-page report and a six-page executive summary.
MnDOT hired inspectors from Michael Baker Jr. Inc., an engineering services firm near Pittsburgh, after Gov. Tim Pawlenty ordered an emergency statewide review of all bridges following the Aug. 1 collapse of the Interstate 35W bridge. The inspectors spent 11 days scrutinizing the 57-year-old Hastings Bridge, which carries about 32,000 vehicles along Hwy. 61 across the Mississippi River every day.
Repair project starts in April
The bridge is not scheduled to be replaced for at least 10 more years, though MnDOT had already scheduled a $2.2 million repair project that will close two-way traffic for more than two months starting in April.
Like the I-35W bridge, the Hastings Bridge has a fracture-critical design. That means that if one load-carrying part fails, the whole bridge will fall.
In a sweeping executive summary, inspectors said that all 2,800 tack welds in the bridge's steel truss are of "very poor quality and exhibit porosity." Seventy-six of those tack welds were found to be cracked. Inspectors recommended that MnDOT keep all tack welds under thorough inspection or "carefully and properly" remove them to stop the cracks from spreading.
MnDOT said Monday that the tack welds have been inspected and will be inspected again this year.
"Tack welds of concern will be removed," said MnDOT spokeswoman Jeanne Aamodt.
In 1994, inspectors found rocker bearings "tipped excessively in contraction." No repairs were indicated. In the August report, inspectors found "additional bearings ... as being in a contracted position."
"The condition appears to be worsening, and could be the result of advanced pier settlement/ rotation," said the executive summary of the inspection report.
The summary also said that one set of bearings was in poor condition and damaged by severe surface corrosion and severe pack rust. The bearings appeared to be "frozen," or inoperable, the inspectors wrote.
Other bridge bearings were found to be missing components, such as one that had four sheared bolts. The inspectors recommended that MnDOT replace all bearings on the bridge with new "state of the art" assemblies. The bearings are designed to distribute weight and allow the structure to move with thermal expansion and contraction of steel.
Aamodt said MnDOT will replace bearings only on one pier and not until the April repair project begins. The agency plans to refurbish, retrofit or clean other bearings that are problematic, but not replace them, she said.
She also said that following the latest inspection, MnDOT has been monitoring the bridge piers for movement every month and will continue the checks leading up to the repair project.
Last month, the Star Tribune found that many flaws noted by inspectors were not repaired for years. In some cases, defects first noted in the mid- to late 1990s had not been addressed through 2006, the last year for which MnDOT provided inspection records.
Annual reviews of the bridge found deficiencies classified as "severe," "numerous," "extensive," and "excessive."
MnDOT says bridge is safe
Bob McFarlin, assistant to MnDOT Commissioner Carol Molnau, said last month that the public should not worry about the bridge's flaws. He said the bridge is safe and repairs are done as warranted.
In 1998, the bridge's deteriorating condition prompted MnDOT to post an individual vehicle load limit of 40 tons. The restriction prevents the heaviest trucks from crossing the bridge.