Regarding the NTSB's statement of January 15, 2008: Today the NTSB investigators of the Minneapolis I 35W Bridge collapse (August 1, 2007) released their findings so far. They feel the gusset plates on the truss were inadequately designed, leading to the collapse of the bridge.
I, on the other hand, know that the approach highway pavement can create a horizontal force of a large magnitude. Reading the inspection reports, engineering studies and physically examining the highway approaches I conclude that when the deck and joints were partially removed, the bridge could not withstand that horizontal force. Separation of the trusses occured at the panel points just past the main river piers, practically simultaneously.
A number of states have introduced a stress relief joint in the highway pavement to mitigate this horizontal force including New York State which employed me as a bridge engineer for 34 years.
Bill Kallman, PE www.myspace.com/billkallmanpe billkallman@charter.net 310 Mesnard Street, Hancock, Michigan 49930
recommend
Facebook
Twitter
bookmark 
email
print
Comments: 2
From what I read, the NTSB is releasing an interim finding not so much as to say why the bridge failed but as a warning for the states to review the design of other bridges.
Their final report may agree with your findings.
Bill,
I thank you for your reports which drew attention to a number of factors involved in the bridge collapse..
In the video from the security camera we see the deck on the Southbound lane of I35 "explode" skyward in fairly small fragments. We also noted the buckling of the roadbed immediately South (SE) of the bridge structure. Another piece of evidence we see is the large slab of roadbed which was formerly on the North bound lane on the bridge structure which was over the river road on the SE bank of the river and which had been "cast" to the ESE of that portion of the total bridge structure which consisted of 3 basic interdependent elements. The main span and its two critical "approach" spans on either end of the main span.
I would have to conclude, as you have, that the emphasis on the plate failures given by the NTSB is erroneous. My conclusion is that the plate failures are a RESULT of other failures which immediately proceeded the collapse of the bridge.
The problem you and I have is 'How in the world does one explain the dynamics of the failure in such a way as to make the analysis comprehendible to those who do not understand structural engineering?'
Bill, try this for example: If a person is using a very long extension on a socket in order to reach a bolt in an "inaccessible" location and the bolt we are attempting to remove requires a large torque to get that bolt "unfrozen", when the bolt does "break free" the resulting "whiplash" in the long extension will break the socket. The initial torque did not cause the socket to fail, but the sudden change in forces (oscillation) does cause the metal to fail.
In the collapse of the I35 bridge, I think we see the same series of dynamic forces in that if the bridge deck was under severe compressive stress, and that stress is suddenly "relieved" as the deck "explodes" from the compressive stresses, the resulting shock waves absorbed by the bridge causes the plates to fail.
Are we both "on the same page" here in our analysis of the failure?
John