"We have never sensed there were any troubles with this particular bridge," agreed Rep. Frank Hornstein of Minneapolis. Both are members of the Minnesota Democratic-Farmer- Labor Party.Hortman speculated that 90-plus-degree heat Wednesday and the above-normal temperatures of the past two summers may have been a contributing factor.
"Did the heat put extra strain on the steel?" Hortman said. "You wonder if this bridge was built to withstand the massive heat we have had this summer." denverpost.com
If a 1,907 foot bridge speced out before 1967,
that a 2001 evaluation of the bridge, prepared for the state transportation department by the University of Minnesota Civil Engineering Department, reported that there were preliminary signs of fatigue on the steel truss section under the roadway, but no cracking, detnews.com...were to undergo an increased range of expansion and contraction due to warmer than unusual summers in Minnesota. Would it fail ahead of projections for replacement after 2012?
All structures have specified tolerances based on what engineers currently know about climate. When you take into account 70,000 bridges in the US that have been found to be structurally deficient and a highway system that is 40-60 years old there are alot of assumptions based on what we "did" know about climate data.
A drastic increase in temperature as a result of a rapid increase in greenhouse gases in the near future might have implications in the longevity of structures built and designed when maximum temperatures were thought to be lower.
Bridge failure is one thing I never would have associated with Global Warming, but it may be something to think about.
One bridge expert stated that his guess was that one of the giant rollers used to account for expansion and contraction of the span on its support got stuck. Unable to move, the forces may have built up with the hot weather sending already fatigued metal into failure.
That scenario would make sense...