A bridge last for 40 years...and it was designed wrong? Makes you think that is NOT the answer.
Read the reports....
It wasn’t Tim nor “W’s” fault.....
You design things with margin. When the margin is lower than expected things can fail unexpectedly even after a long time. Clearly the bridge failed. Assuming it was maintained and the soil didn’t fail that leaves the bridge itself as the source of the failure.
Fatigue can make the difference.
I got all interested in this in the aftermath, and studied the reports available on the internet, and I feel they have completely bypassed the maintenance issue. As I pointed out earlier, the FATIGUE EVALUATION AND REDUNDANCY ANALYSIS for Bridge No. 9340, I-35W over Mississippi River, July 2006, cites important maintenance problems, which it unaccountably ( to me ) dismisses lightly. I refer to the roller bearings at the base of the columns, which are major design elements of the bridge. The report states there was “dirt packed into various areas of the bearing.” and “All the roller bearings seem to have thick coatings of paint and did not appear to be functioning as intended under live load.” This last phrase was a euphemism, admitting only that the bearings could not adjust from moment to moment, when in fact they were “frozen” for months, and possibly years. Under extreme thermal stress, they could give way and cause the entire bridge structure to “spring”.
Incredibly ( in hindsight as it may be ) this analysis accounts only for the static conditions, admitting “the actual force-displacement relationship of the bearings is nearly impossible to charactize.” So, “In the computer modeling, two extreme bearing bearing conditions were investigated for their impact: 1) the ‘as-designed’ condition based on the plans; and 2) the fully ‘locked’ condition.”
This ‘locked’ conditon refers to the bearings “frozen” by rust, dirt, and paint. But what if the rust, dirt, and paint should suddenly give way ?
I personally believe that this is exactly what happened.