There is much discussion in the engineering community. There were detected 0.25" long cracks in the bridge bearings. These are the connection points between the truss and the substructure (piers). It was these cracks among other deficiencies which caused the bridge to be poorly rated.
Also, the bridge was being resurfaced. Resurfacing entails removal of the existing superstructure surface, likely with jack hammers. Speculation is that the jerk caused by the hammers caused the catastrophic failure of one of the bearings. Such a failure would cause the superstructure to move perpendicular to the direction of travel (the lateral shift mentioned by the head of the NTSB) and eventual collapse of the entire structure. My coworkers mention a particular bridge in Alabama with the same problem that is due to be resurfaced this fall (no pun intended). Terry On 8/4/07, R.C.Macaulay <[EMAIL PROTECTED]> wrote: > > > Howdy Vorts, > > Rather surprised that one of our structural engineers in the group has not > posted a comment on the Minneapolis bridge collapse. > > Truss bridge designs have an inherent weakness at the joints. Used to use > rivets back then. It does require a stretch to accept the premise that a > single joint failure could result in such a chain reaction free fall. I > could almost buy a series of failures given a time frame but the US Corps of > Engineers vid shows the whole shebang dropping together.. hmmm. > > I used to be sucha trusting soul ..but.. after bldg 7 world trade center > collapse... well.. > > Richard > >
