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Re: Gusset Plates in a 3rd Minnesota Bridge (Blatnik Br) are Found to be Faulty

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Dear SEA-INT Friends:

It turns out that for this case of Blatnik bridge in Minnesota, in 1993, they have added 2 inches of "wearing surface" (concrete layer) to the deck. This is what was also done in I-35W and DeSoto Bridge. In my opinion, this additional layer of dead load is not the main culprit in creating these gusset plate problems, but one of the little storms that in case of I-35W added to other little and big storms and made the "perfect storm that broke the back of that bridge crushing 13 people to their violent and very tragic death.

I like to add that the seriousness of the problem here cannot be under-estimated. These determinate trusses of what I call "the second generation of steel bridges" (built right after world war II and before 1970's when we understood the fatigue phenomenon in steel bridges) are like house of cards waiting for a few individual deficiencies to add up, eliminate a member or gusset plate and the entire span to collapse progressively. What is urgent to do is to identify these bridges (apparently there are about 460+ of bridges of this type) and do a in-depth investigation and field inspection and study of their fracture critical members and connections to find out the problem and correct the situation before it is too late for some other commuters using these bridges. One hopes the steel industry will take the lead on this and while acknowledging the problem, which is quite limited anyway, find sound and economical solutions for it. AISC so far has not stepped forward, perhaps out of fear that if the problem is acknowledged, no bridge builder will build steel truss bridges and all will be lost to concrete! I think they underestimate grossly the wisdom of bridge and structural engineer. They only use a system that is safe and economical and performs well during the service life. No matter how much public relations one puts up, when a truss bridge such as I-35W collapses and all photos of the collapse show the majestic reinforced concrete arch bridge of 1930's (the 10th Street Bridge parallel to I-35W) is standing tall and looking down on this collapsed bridge, no matter what we do, the people of Minneapolis would have a second thought in using steel bridges, even very majestic cable supported or arch bridges of steel. And, that is what exactly they did. Chose a totally unimpressive bland R/C box girder replacement. Like to hear from you on what you think and how best we can protect public using our structures given the limited resources we have?

Sincerely

Abolhassan Astaneh-Asl, Ph.D., P.E., Professor and
Consultant on Structural and Earthquake Engineering and Protection of Buildings and Bridges against Blast and Impact
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Dear SEA-INT Friends:

For those of you who are interested in bridges , the Minnesota DOT has just announced that the gusset plates in the Blatnik Bridge (on I-535/HW53) has gusset plate problems , which from what they have said , to me, appears to be "edge buckling" problem. This is similar to what was photographed in 2003 to have occurred in I-35W bridge (collapsed on August 1, in 2007 resulting in 13 deaths and more than 100 injuries) and recently in DeSoto Bridge (closed for demolition and replacement) without any injury. The Blatnik bridge is a 1961 steel truss arch bridge about 8000 feet total length. MN DOT is planning to close certain lanes and repair/retrofit the gusset plates by adding angle stiffeners to the free edge of gusset plates.

You might wonder what s going on in Minnesota and why all these steel truss bridges are having gusset plate problems. Well, being a little bit familiar with gusset plates and steel truss bridges, this is a nation-wide problem and most likely the reason Minnesota DOT is finding out about these problems is that they are looking at their gussets!

Also, having worked on I-35W and the DeSoto bridge since last year, I feel that adding an inch or two of additional resurfacing concrete ( which was done in both cases) is not a good idea unless you check the stresses and find out that even with that additional dead load , the AASHTO factors of Safety are in place.

Sincerely

Abolhassan Astaneh-Asl, Ph.D., P.E., Professor and
Consultant on Structural and Earthquake Engineering and Protection of Buildings and Bridges against Blast and Impact
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