UPDATE: Turns out this was a legitimate question to ask — the feds did examine this issue in detail, but ultimately concluded it was not a factor (see their final report here, page 126).
I got a little flak when I made a similar suggestion back in August, prompted by my Minneapolis-based brother. So I will try to report as neutrally as possible on an article in the Minneapolis Star Tribune just sent to me by said brother, headlined:
Did heat, rusted plates doom bridge?
Federal investigators are trying to determine whether 91-degree heat caused expansion that put too much pressure on the corroded gusset plates that held the I-35W span together.
What does the article say?
… authorities are analyzing what role the 91-degree heat on Aug. 1 might have played in increasing stress on the already-weakened L-11 gusset plate, which connected four steel beams located near the bridge’s south end.
Like the New Orleans levees that failed during Katrina, this bridge was not well-designed. In particular, it apparently could not handle the consequences of the cold and heat that Minneapolis is subjected to:
One of the structural engineers who has viewed the wreckage and knows the design of the bridge said runoff of salt and de-icing chemicals from the bridge deck could have contributed to the corrosion in the L-11 gusset-plate connection. That’s because a diagonal, H-shaped beam running into the joint could have acted to channel the liquid toward the gusset plate, the engineer said.
If so, the response to cold Minneapolis winters set the stage for a hot summer failure:
Both structural engineers interviewed by the Star Tribune … say federal authorities are examining whether intense heat on Aug. 1 triggered a chain reaction of force that overpowered gusset plates in crucial locations — such as the one at L-11.
The I-35W bridge was designed to flex, to handle expansion in extreme heat and contraction in bitter cold. But that design assumed that roller bearings would move accordingly.
Roller bearings are mounted on top of bridge piers. They support the weight of the bridge and contain steel cylinders that allow the bridge to roll smoothly back and forth as it expands and contracts with temperature changes.
MnDOT officials had long known from their inspections that the bearings were not working correctly because of corrosion and buildup of debris. And in July 2006, a consultant’s report highlighted the problem. “The bearings are not allowing the structure to move linearly with changes in the … temperature,” the report said.
Roller bearings recovered from the river are stacked neatly in the NTSB’s secure area for inspection. One of the structural engineers who asked not to be named said the bearings appear to be lacking marks of wear, indicating they may have been locked up or their movement restricted by debris and corrosion.
Does this mean climate change contributed to the Minneapolis bridge collapse? We don’t know the final answer to that yet, but it certainly seems now like it was a not unreasonable question to ask after all.
One thing is clear — global warming means more extreme weather in the future, and our infrastructure designers need to plan accordingly. Reassuringly, Minnesota public radio ran a segment titled, “Can the new bridge stand the heat?” (available here) where they interviewed Linda Figg, the lead designer of the I-35W bridge replacement project, “about how the new I-35W bridge will be designed to withstand Minnesota’s extreme winters and summers.”
I am not an “I told you so” type of person — well, maybe a little (isn’t that one of the central points of blogging?), but my brother is a “your blog on the matter was well ahead of the curve” type of person. Okay, ’nuff said.
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I’ve got my theory on the bridge collapse. I drove across the bridge about 3 times a week and every time I did, I thought of how stupid it was to close off the east 2 lanes of both northbound and southbound traffic for the resurfacing. They should have closed the 2 outside lanes on the northbound and southbound traffic and run the traffic on the inside 2 lanes of the northbound and southbound traffic. After resurfacing those, they should have closed the 2 inside lanes of northbound and southbound traffic and then resurface the outside 2 lanes of northbound and southbound traffic.
The way they did it meant all the weight of traffic and resurfacing trucks and loads was on the west side of bridge with no loads pushing down on the east side of the bridge. The lower east side of the bridge blew out to the east, just as would be expected if all the forces downward was on the west side of the bridge. They maybe didn’t calculate those stresses enough when they designed the bridge many years ago.
From what I have read, the unbalanced loading on the bridge during resurfacing is being looked at as a cause of the collapse.
Joe, I know you’re the only person who will probably ever read this post, but remember what I said in the original thread? Well, here are the results -
http://ap.google.com/article/ALeqM5goB9pwml7xJ3rY1RFgsuvJB_TQ7AD8U6GP880
Gov’t: Design Flaw in Bridge Collapse
By FREDERIC J. FROMMER – 2 hours ago
WASHINGTON (AP) — Undersized gusset plates in the Interstate 35-W bridge in Minneapolis were “the critical factor” in the bridge collapse last year that killed 13 people and injured 100, the National Transportation Safety Board said Tuesday.
Chairman Mark Rosenker said the plates, which connected steel beams, were roughly half the thickness they should have been because of a design error. Investigators found 16 fractured gusset plates from the bridge’s center span, he said.
“It is the undersizing of the design which we believe is the critical factor here. It is the critical factor that began the process of this collapse. That’s what failed,” Rosenker said.
The Minneapolis bridge was a steel-deck truss bridge that opened in 1967. Rosenker said it wasn’t clear how the design flaw made it into the bridge because investigators couldn’t find the design calculations.
Once they made it into the completed bridge, he said, there was little chance they would be noticed by inspectors.
There are about 465 other steel-deck truss bridges around the country. Rosenker said the safety board had no evidence that the deficiencies in the Minneapolis bridge design “are widespread or go beyond this bridge.”
But he cautioned that states and contractors should look at the original design calculations for such bridges before they undertake “future operational changes.”
The Minneapolis bridge was deemed “structurally deficient” by the federal government as far back as 1990, and the state’s maintenance of the structure has been questioned. But Rosenker said the NTSB investigation has found no evidence that cracking, corrosion or other wear “played any role in the collapse of the bridge.”
Investigators also found no flaws in the steel and concrete material used in the bridge.
In his update Tuesday, Rosenker also noted structural weight had been added to the bridge in two major renovations, as well as construction materials that were on the bridge the day it collapsed as part of a resurfacing project.
The findings are consistent with what the NTSB said about a week after the Aug. 1 collapse, in which the bridge plunged into the Mississippi River. At the time, the NTSB said it had found issues with the collapsed bridge’s gusset plates, but expected a full investigation to take more than a year.
Transportation Secretary Mary Peters was expected to issue an advisory urging states to check the gusset plates when modifications are made to a bridge — such as changes to the weight of the bridge or adding a guardrail, said a federal official with knowledge of the plans. The official spoke on condition of anonymity because Peters had not yet made the announcement.
Currently, such calculations are done for the entire bridge, but not down to the gusset plates, the official said.
Last August, Peters advised states to consider the additional stress placed on bridges during construction projects. An 18-person crew was working on the bridge when it collapsed.
Nearly three months later, she told a gathering in Washington of a “working theory” of a poorly designed gusset plate and a heavy load of construction materials.
Meanwhile, state lawmakers announced plans last month to spend up to $500,000 to hire legal counsel to aid in a legislative inquiry into the collapse.
Late last year, President Bush signed a massive spending bill which included $195 million to help replace the bridge. That came on top of the $178.5 million the federal government has already given Minnesota for the project.
The bridge was originally designed by Sverdrup & Parcel, a company acquired in 1999 by Jacobs Engineering Group Inc. of Pasadena, Calif. A message left by The Associated Press with Jacobs wasn’t immediately returned.
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DUH!
You go guy.
Ron — Please read your comments before posting them. I am going to delete all petty and gratuitous insults.
Ron — again.