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RE: Old Seismic Values

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For general comparison of code seismic formulas:

V = (Sds*W)/(R/I) = 2.5*(0.40*Sds)(W)/(R/I)	2000 IBC 
V = 2.5*Aa*W/R 						1996 BOCA
V = 2.5*Ca*I*W/R = 2.5*Ca*W/(R/I) 			1997 UBC
V= Z*I*C*W/Rw = C*Z*W/(Rw/I) 				1994 UBC

In these formulas, 0.40*Sds, Aa, Ca, and Z represent effective design ground
acceleration. Prior to the 2000 IBC, codes typically based ground
accelerations on 10 percent probability of being exceeded in 50 years. The
2000 IBC bases Ss on 2 percent probability of being exceeded in 50 years;
but Sds is based on 2/3*Ss, so you really are not designing for the full
effects of the more infrequent earthquake. 


William C. Sherman, PE 
(Bill Sherman) 
CDM, Denver, CO
Phone: 303-298-1311
Fax: 303-293-8236
email: shermanwc(--nospam--at)cdm.com
 

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