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Re: Roof Equipment

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On average, the 1997 UBC F-sub-p equation has been calibrated to be 1.4
times bigger than that from the 1994 UBC, the difference between the
allowable stress EQ and the strength EQ.  Your C-sub-a value of 0.57
indicates that you must be seeing the effects of the near-source factor
N-sub-a.  In that case, you should be seeing the same increase in your
structure loads.  Your increase from the old codes is due to the seismic
coefficient C-sub-a, not Equation 32-2.

Rick Drake, SE
Fluor Daniel, Aliso Viejo, CA


                    "Larry Hauer"                                                                                  
                    <lrhauer@earthl      To:     "seaint" <seaint(--nospam--at)>                                      
                    04/03/01 12:45       cc:                                                                       
                    Please respond       Subject:     Roof Equipment                                               
                    to seaint                                                                                      

What is the common practice for anchoring roof top  mounted equipment based
on the '97 UBC? Per Table 16-O, 3),C), an Ap of 2.5 and  Rp of 3.0 is
required. Using Formula 32-2 with Ca=0.57, I'm coming up with  1.36W,
(ASD). Has it really increased this much over the older  codes?

Thanks in advance,

Larry Hauer, S.E.

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