The complete, total and uniform failure of the center span is difficult to reconcile. One might expect the span to fall to one side or to fall to one end. The center span sits on only four bearings. Being of non-redundant cantilever construction the other sections were not self supporting and also failed when the center span gave way.
The real time video clearly shows a nearly uniform failure of the entire center section. What is amazing is that both ends of the bridge detach at almost the same time.
http://www.youtube.com/watch?v=EjCic0YlJwQ
The critical points appear to be the four bearings that the center section sits on. If just one bearing moves or breaks a collapse will occur.
Here is my scenario
- Steel corrosion of the trusses and especially the bearings weakens the steel trusses and creates misalignment of the bearings.
- Cold weather reduces the ability of the steel to flex which induces cyclic fatigue stress cracks. (Hoan bridge failure in 2000)
- De-icing of the bridge deck with various corrosive agents further attacks the steel and the bearings.
- Recent spate of high temperatures and poor maintenance of the expansion joints results in the expansion joints being “locked up”.
- Lane closures, stationary traffic and repaving equipment creates an asymmetrical load on the bearings.
With some or all of the expansion joints clogged with dirt and debris a tremendous load is building across the top of the bridge. This unplanned top loading is creating excessive stress in some areas of the bridge and actually relieving stress on other components of the bridge. Asymmetrical loading due to the lane reductions is further contributing to the uneven loading of the bridges and misalignment of the bearings. Distribution of heavy trucks and construction vehicles on one end and or side of the bridge further contribute. Some or all bearings are not sitting in full contact in their pockets. At this point a bearing or truss support which has been weakened by corrosion and stress cracks has a catastrophic failure. Other trusses or bearings let go within a fraction of a second and the whole center section falls to the river in one piece.
Eye of Unk makes an interesting observation regarding the construction vehicles and harmonics. Very interesting.
Lastly, I also think we are going to hear a lot more about expansion joints.
Jury selection begins in Elzahabi trial.
This dude was arrested in 2004.
Just don't want to be too quick with the "terrorism" impossibility.
There are a few articles on this guy that are worth reading and pondering.
Somewhat disagree. Every bridge I am aware of (I used to inspect them and supervised other inspectors afterward) has bad expansion joints. Every one of them is rusted and most are totally locked up. It sometimes causes localized failures, particularly on the deck if it is concrete, however, I have never heard of that being a primary cause of failure.
My bet is a fatigue crack that was hidden or missed during inspection. The combination of bumper-to-bumper traffic and the construction machinery was more than the remaining tension (the uncracked area) could take.