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- Subject: wind
- From: Michael Hemstad <mlhemstad(--nospam--at)yahoo.com>
- Date: Tue, 25 Feb 2003 07:31:14 -0800 (PST)
I'm trying to get familiar with the IBC wind load provisions. I have run a comparison between the IBC provisions, ASCE 7-98, and the 1997 UBC. The results are a little dismaying, especially the IBC values. Can someone tell me if I've made a mistake somewhere? The analysis is for a fictitious 42 foot tall building in Minnesota, Exposure C. Iw = 1.0; topographic constant 1.0. The building is enclosed, with a flat roof. IBC 1609.6: V = 90 mph Table 1609.6.2.1(1) (Interior Zone Wall) gives pressure = 8.5 psf Table 1609.6.2.1(4) gives Ht+Exp coeff = 1.51 load factor = 1.6 w = 12.84 psf, x 1.6 = 20.5 psf If instead I use the last columns of Table 1609.6.2.1(1), I get a pressure of 7.2 - (-5.8) = 13.0 psf. Then, w = 19.63 psf, x 1.6 = 31.4 psf ASCE 7-98 Simplified Procedure (shouldn't be used since ht > 30 feet) Fig. 6-1: v = 90 mph Table 6-2 give p = 14 psf Exp. C multiplier = 1.40 load factor = 1.6 w = 19.6 psf, x 1.6 = 31.4 psf ASCE 7-98 Analytical Procedure Figure 6-1: v = 90 mph Table 6-6 gives Kd = 0.85 Table 6-5, Case 1 gives Kh = 1.05 Figure 6-4 gives GCpf = 0.40 - (-0.29) = 0.69 Table 6-7 gives GCpi = 0.18 qh = 18.51 psf load factor = 1.6 w = 18.51 x (0.69 + 0.18) = 16.1 psf, x 1.6 = 25.8 psf 1997 UBC Fig. 16-1: v = 80 mph (fastest-mile, not 3-second) Table 16-F: qs = 16.4 psf Table 16-G: Ce = 1.32 Table 16-H: Cq = 0.8 + 0.5 = 1.3 load factor = 1.3 w = 28.14 psf, x 1.3 = 36.6 psf Factored loads vary from 20.5 psf to 36.6 psf. Nice tight grouping. Can anyone tell me if these values seem right? In the IBC calcs, I assume the higher value is the one to use. What is the lower value for? Where does it say this? In the ASCE 7 Analytical Procedure, footnote 3(ii) of Table 6-7 indicates GCpi is applied to all interior surfaces. Thus, it should cancel out for the MWFRS. However, Section 6.5.12.2 indicates it is additive to the exterior pressures for the MWFRS. Can someone shed some light on that? Thanks for any help. Mike hemstad TKDA st. Paul, Minnesota __________________________________________________ Do you Yahoo!? Yahoo! Tax Center - forms, calculators, tips, more http://taxes.yahoo.com/ ******* ****** ******* ******** ******* ******* ******* *** * Read list FAQ at: http://www.seaint.org/list_FAQ.asp * * This email was sent to you via Structural Engineers * Association of Southern California (SEAOSC) server. To * subscribe (no fee) or UnSubscribe, please go to: * * http://www.seaint.org/sealist1.asp * * Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you * send to the list is public domain and may be re-posted * without your permission. Make sure you visit our web * site at: http://www.seaint.org ******* ****** ****** ****** ******* ****** ****** ********
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