Unknown force
Keith A. Thomas
Saturday, September 1, 2007
WHEN THE Minneapolis bridge and all other bridges were designed, there were future unknowns that naturally were not considered or factored into the equation. The force that brought the bridge in Minneapolis down could easily damage any bridge now standing and should be controlled with regulations for threatened bridges.
The previously unknown or unconsidered force that is now a major problem is forward or backward thrust that is caused by trucks and cars when braking. When trucks and cars apply their brakes, this becomes forward or backward thrust. It is possible that millions of pounds of thrust could exist on any bridge under certain conditions when traffic is throbbing through construction zones or under adverse conditions causing an immediate or future failure. I have seen as many as 10 big trucks loaded with asphalt backing together for a position to unload. When one stops, they all stop together. With this much tonnage moving and stopping in unison, this creates an enormous stress. The same is true when traffic throbs through work zones. It is possible that this is the force or one of the forces that brought the bridge down.
It goes without saying that one section of failure should not affect the integrity of another section when properly designed. However, there needs to be new regulations that all traffic must remain in a more controlled motion when on threatened bridges.