I think it was originally opened with six lanes, and had been upgraded to eight lanes, something common for bridges as traffic lanes are widened. . Also, the interstate system originally had limits of 60k lbs or so for trucks, while 80k seems common these days.
I-35 Bridge Collapse
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Yeah, another good point is that when this bridge was first opened it may have been more than adequate at the time. I am not familar with that area. 40 years ago the cities in that area and the population of the state may have been much less. But certainly today the cities there are major cities and need major bridges.
You need to be able to predict the future needs if possible. If the bridge was designed to handle only 6 lanes at first and then they went to 8 lanes without upgrading the bridge there is only so much a structure can take if it is not designed for the increased load.
But I still do not like the looks of this bridge. I have seen better designed smaller bridges that handle a lot less traffic. Of course, 40 years ago the cities in this area may have been much smaller and the tax base may have been a lot less. Maybe that was the best bridge they could afford and they thought at the time it would be adequate for a reasonable bridge lifetime.
And the bridge may have been let down by inadequate inspections and dirty dealing behind the scenes. Who knows? There are going to be a lot of investigations, lawsuits, hearings, etc. I imagine if there was some dirty dealing it will come out eventually. There are 5 people confirmed dead, some people missing who are likely dead, a lot of people injured, and a lot of property damage and cities trying to find alternative traffic routes. So it is likely that it will all come out in the wash. The replacement bridge will likely be built a little bit better.
You need to be able to predict the future needs if possible. If the bridge was designed to handle only 6 lanes at first and then they went to 8 lanes without upgrading the bridge there is only so much a structure can take if it is not designed for the increased load.
But I still do not like the looks of this bridge. I have seen better designed smaller bridges that handle a lot less traffic. Of course, 40 years ago the cities in this area may have been much smaller and the tax base may have been a lot less. Maybe that was the best bridge they could afford and they thought at the time it would be adequate for a reasonable bridge lifetime.
And the bridge may have been let down by inadequate inspections and dirty dealing behind the scenes. Who knows? There are going to be a lot of investigations, lawsuits, hearings, etc. I imagine if there was some dirty dealing it will come out eventually. There are 5 people confirmed dead, some people missing who are likely dead, a lot of people injured, and a lot of property damage and cities trying to find alternative traffic routes. So it is likely that it will all come out in the wash. The replacement bridge will likely be built a little bit better.
Yes, this was not a good bridge design by current standards, but the fact of the matter is they were designed and constructed all over, and many of the type still remain in service today. Would a similar design be done today? Not likely. We've learned too much since then to keep doing things the same way.
Cetainly this bridge was exposed to a climate that was harsher than many bridges experience, but no different in temperature extremes, snow, etc... than bridges throughout the state. The major issue that plagued the driveability of the bridge over the years was the constant moisture that was availible that caused serious black ice problems in the winter. The moisture was availble by virtue of St. Anthony Falls on the Mississippi River and a nearby heating plant. The moisture probably has played a role in overall corrosion of the bridge.
The black ice issues were severe enough that an automatic deicing system was installed in 1999. Since 1999, our usual deicer of Sodium Chloride (Salt), that we use everywhere else, was replaced by Potassium Acetate on this bridge. Theoretically, Potassium Acetate is supposed to be much less corrossive, making its use attractive on the bridge.
Overall, this bridge has certainly had its issues up to the point it failed and its poor design was part of why it was inspected on a yearly basis. The inspection crews through the years look like it has had many of the same folks associated with it - did over familiarity with the bridge lead to missing something?
I'm confident that a solid answer to the reason for the failure will be found and we'll all learn from it. With the video evidence, lots of information collected over the years, and several concurrent investigations happening, hopefully that will be the conclusion.
Cetainly this bridge was exposed to a climate that was harsher than many bridges experience, but no different in temperature extremes, snow, etc... than bridges throughout the state. The major issue that plagued the driveability of the bridge over the years was the constant moisture that was availible that caused serious black ice problems in the winter. The moisture was availble by virtue of St. Anthony Falls on the Mississippi River and a nearby heating plant. The moisture probably has played a role in overall corrosion of the bridge.
The black ice issues were severe enough that an automatic deicing system was installed in 1999. Since 1999, our usual deicer of Sodium Chloride (Salt), that we use everywhere else, was replaced by Potassium Acetate on this bridge. Theoretically, Potassium Acetate is supposed to be much less corrossive, making its use attractive on the bridge.
Overall, this bridge has certainly had its issues up to the point it failed and its poor design was part of why it was inspected on a yearly basis. The inspection crews through the years look like it has had many of the same folks associated with it - did over familiarity with the bridge lead to missing something?
I'm confident that a solid answer to the reason for the failure will be found and we'll all learn from it. With the video evidence, lots of information collected over the years, and several concurrent investigations happening, hopefully that will be the conclusion.
This bridge, in Michigan's U.P. was reported as similar design to the MN bridge. They checked it since the collapse and gave it a good bill of health.
http://www.michigan.gov/mdot/1,1607,7-151-9620_11154_11188-29665--,00.html
http://www.historicbridges.org/truss/us2/photos.htm
The first link won't paste in correctly, try using it "manually" ie, copy it then paste it into your "window".
The second link has some nice underneath pictures for you engineers. This is light traffic, 2 lane bridge. LOOK AT THE JOINTS SITTING ON THE LARGE PIERS TOWARDS THE BOTTOM OF THIS PAGE.
http://www.michigan.gov/mdot/1,1607,7-151-9620_11154_11188-29665--,00.html
http://www.historicbridges.org/truss/us2/photos.htm
The first link won't paste in correctly, try using it "manually" ie, copy it then paste it into your "window".
The second link has some nice underneath pictures for you engineers. This is light traffic, 2 lane bridge. LOOK AT THE JOINTS SITTING ON THE LARGE PIERS TOWARDS THE BOTTOM OF THIS PAGE.
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