Yesterday, I wrote about the NTSB's new interest in the gusset plates that held the St. Anthony Bridge's girders together as a possible cause of its collapse. The Cleveland Plain Dealer reports today on a near-collapse of an Ohio bridge that started with construction work and ended with failed gusset plates eleven years ago (h/t: CQ commenter Mike):
Two failed bridges. Two scarily similar scenarios.
Last week, the Interstate 35W span over the Mississippi River in Minneapolis collapsed under the weight of rush-hour traffic and construction crews. Federal investigators now wonder whether the design of steel plates joining beams is to blame.
Eleven years earlier, the eastbound I-90 bridge over the Grand River in Lake County failed. The reason: the same steel plates, called gussets. They had corroded, then buckled after crews blasted them during painting preparations. ...
The spans are Warren truss bridges, made of diagonal compression members joined by gussets. Both bridges are nonredundant, meaning that if one part fractures, the whole structure can fall down. At the time of the failures, both bridges had work crews and equipment weighing them down.
Was this a missed warning sign? It's hard to know for sure. The NTSB apparently didn't think so at the time, and they had some good reason for that conclusion. The Ohio bridge incident differed in some particulars. For one, it wasn't rated for the kind of heavy construction equipment that the crew had parked on it during the work. Secondly, they used steel shot to blast away corrosion from the superstructure during the work, which seriously degraded the integrity of the gusset plates. Nothing like that had been done to the St. Anthony Bridge before its collapse.
Still, the similarities seem rather compelling. Once the Ohio bridge had one gusset plate fail, a number of them bowed outward. No one seems to know why the entire bridge didn't fail, but it did sink three inches and had to be closed for almost six months. It calls into question whether the NTSB should have reconsidered the Warren truss design and warned states of potential issues with the thickness of gusset plates on similar bridges, such as the St. Anthony Bridge in Minneapolis. Ohio focused more of their inspection on these plates after the 1996 incident, but the word did not appear to get to other states.
There are no national specifications for gusset plates, either. Designing support structures is part science and part art, as designers have to assume many variables for use, traffic weight, age, and corrosive elements in the environment. However, the St. Anthony Bridge had a uniquely long span over the river with no center supports. As the Plain Dealer notes, there are no charts for correct specifications on gusset plates.
In other news, divers retrieved three bodies from the river yesterday, including a mother and he baby and a man who died trying to save others:
Peter Hausmann, a father of four from Rosemount, survived the collapse and escaped from his van into the murky, turbulent waters, according to a source involved with the investigation. In the resulting chaos, he apparently swam toward victims in another vehicle in an attempt to render assistance, the source said. ...
Hausmann spent about three years doing missionary work in Kenya and maintained ties to Africa, working on AIDS projects and building a church. If he was trying to rescue someone, it would be typical of Hausmann's selflessness, his friends and co-workers said. "Pete is the type of guy who would do anything to help someone," said Jeff Olejnik, Hausmann's boss at Assurity River Group in St. Paul.
Another friend echoed that sentiment. "That would be Pete," said Gerry Fisher, a friend and former co-worker of Hausmann. "If there was a last act of Pete on this Earth, that certainly would be consistent [with who he was]."
The other two victims identified were Somali immigrant Sadiya Sahal and her 22-month old daughter Hana. The Star-Tribune has a heartbreaking photo of Sadiya and Hana, and published a portion of a letter Sadiya wrote about how excited she was to come to America for a better life. Both stories put the tragedy in stark personal terms, and reminds us how many people will need healing and support from this community.
UPDATE: Numerous commenters and e-mailers point out the obvious, which is that the salt water mentioned in the article would have come from road salt during the winter, which is also true here in Minneapolis. I took out that "difference" from the paragraph above. Also, the other gusset plates bowed outward, not "blowed".