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Re: UBC97-- Redundancy Factor[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org
- Subject: Re: UBC97-- Redundancy Factor
- From: Roger Turk <73527.1356(--nospam--at)compuserve.com>
- Date: Sat, 27 Feb 1999 14:16:26 -0500
Redundancy, when applied to structures, means that there are alternate load paths should any one structural member fail. Years ago in Great Britain, a gas explosion blew out the walls of an upper level corner apartment in a high rise apartment building which caused the floors above it to collapse and take out the all the corner apartments below. IIRC, the floor system was simply supported precast concrete planks and the walls were masonry bearing walls. Once a bearing wall was gone, there was no support for the concrete planks which collapsed on the lower apartments, overloading the bearing walls and causing them to collapse. As a result of this explosion, there was a great push for redundancy, particularly in Great Britain. Once again, IIRC, the British codes required considering any member failing and providing alternate load paths with the forces in the remaining members being no greater than 150 percent of the allowable forces. In the U. S., the precast industry came up with providing negative moment reinforcing across supports to try to support the slab as a cantilever. Calculating alternate load paths considering *any* member to fail (be removed from the structure) is very difficult and time consuming although with computers it is much more achievable that it was with hand calculations. However, IMO, that is the only way to say that a structure has redundancy. With regards to stability, codes do not permit using an identical member to provide lateral support. Nor should we consider an identical member that may be subjected to the same loads as a failed member as providing redundancy. A. Roger Turk, P.E.(Structural) Tucson, Arizona P.S. To our British colleagues: If I pulled wrong information from the deep recesses of my mind, please feel free to correct the information.
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