MnDOT officials had concerns about the I-35W bridge over the Mississippi River last winter, focusing on the same fatigue and potential cracking that has grabbed the focus of the post-collapse coverage. Engineers debated whether to apply patches to the more worrisome points of fatigue, but in the end, opted to continue inspections instead:
Structural deficiencies in the Interstate 35W bridge that collapsed Wednesday were so serious that the Minnesota Department of Transportation last winter considered bolting steel plates to its supports to prevent cracking in fatigued metal, according to documents and interviews with agency officials.
The department went so far as to ask contractors for advice on the best way to approach such a task, which could have been opened for bids later this year.
MnDOT considered the steel plating at the recommendation of consulting engineers who told the agency that there were two ways to keep the bridge safe: Make repairs throughout the 40-year-old steel arched bridge or inspect it closely enough to find flaws that might become cracks and then bolt the steel plating only on those sections.
Fears about bridge safety fueled emotional debate within the agency, according to a construction industry source. But on the I-35W bridge, transportation officials opted against making the repairs.
Officials were concerned that drilling thousands of tiny bolt holes would weaken the bridge. Instead, MnDOT launched an inspection that was interrupted this summer by unrelated work on the bridge's concrete driving surface.
In the rush to point fingers, we have heard from experts on local and national television about the neglect of our infrastructure. Our local crank at the Strib decided to write a column blaming everyone from Tim Pawlenty to David Strom for killing the victims of the collapse. Instead, it looks like the engineers at MnDOT simply decided that the bridge did not appear to have sufficient problems for immediate intervention.
That was not a question of money. MnDOT officials, according to the Strib, acknowledged that they had the money in the budget to pay for the suggested repairs. In fact, MnDOT was the agency that made the determination that the I-35W bridge would not need an overhaul or replacement until 2020. Those recommendations were forwarded to the state government, which didn't have any reason to reject the evaluations supplied by the MnDOT engineers.
This could explain why Pawlenty has decided to outsource the new bridge inspections. He announced yesterday that all Minnesota bridges would undergo an extra and immediate round of inspections. At the same time, he also announced that the state had hired a consultant firm to review the inspection process and to conduct inspections themselves.
Some still insist that it must have been all about money, but MnDOT itself insists that was not the issue. They did not want to risk the bridge structure by drilling the necessary holes in the girders that would have allowed them to rivet repair plates in place. They felt the situation was not critical and that the repair could have made the structure even more unstable.
It doesn't appear that money or neglect played a part in this collapse. It looks instead that MnDOT either didn't evaluate the bridge properly, or that the fatigue it noted didn't have anything to do with the collapse.