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Seismic Zone 1 - U. L. Steel Beam Substitution[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org
- Subject: Seismic Zone 1 - U. L. Steel Beam Substitution
- From: rlewis(--nospam--at)techteam.org (Richard Lewis)
- Date: 29 Mar 1999 21:48:40 GMT
I am sending this out again with the Seismic heading because nobody responded to the first message. It seems everbody responds to a Seismic question so I thought I would give it a try. By the way, it really is in Zone 1! I am confused about a U.L. floor assembly. I have a floor assembly of say U.L. D902 which states the minimum beam size is a W8x28. Now if you scan through the book you find that most beams are a minimum of W8x28. In the front of the manual it states: "For fire resistance purpose, the minimum beam size is expressed in terms of a W/D ratio, where W is the weight of the beam per lineal foot and D is the perimeter of protection material at the interface between the steel section and the protection material. Accordingly, beams of the same configuration and having a greater W/D ratio than the beam size specified in the fire resistive design are considered larger than the specified minimum size beam and may be used in that design." So, I interpret this to take the weight of the beam and divide it by the perimeter of the beam section, minus the top flange width which is against the slab/deck. If I want to substitute a deeper beam in this W/D ratio, I must use a heavier beam than the 28 PLF because a deeper beam will increase the 'D' value which reduces the W/D ratio. Now I know I have used beams smaller than 28 PLF in previous designs and nobody has ever questioned it. Have I always been wrong using beams lighter than 28 PLF that are spray fireproofed? Am I interpreting this wrong? Is there a table somewhere that already has all of the W/D ratios figured out? Thanks for your help. __________________________________________________ Richard Lewis, P.E. Missionary TECH Team rlewis(--nospam--at)techteam.org The service mission like-minded Christian organizations may turn to for technical assistance and know-how.
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