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Posted: Sat Dec 20, 2003 11:16 am Post subject: IS 6533
Hello Mr. Kadam I think hourly mean wind (8.2 of IS 875) is to be used only with gust factor method for dynamic effects. We are converting basic wind speed (which is peak gust speed averaged over a time period of 3 seconds) into hourly mean speed (maximum wind speed averaged over 1 hour) by multiplying it with factor k2 of Table 33 of IS 875.
Then we calculate the force ( 8.3 IS 875) using gust factor which gives the peak load. In case of static load calculation the factor k2 (Table 2 of IS 875) is the variation of basic wind speed with terrain, ht and structure size. Then we calculate the force by using design pressure (=0.6* Vz(=Vb*k*1k2*k3)*Vz) . So what I understand is, the gust factor is 1 for static case (as we are using peak gust speed here) and the gust factor is more than 1 for dynamic effects (as we are using hourly mean wind speed here).
So for chimneys static analysis should be done as per 5 of IS 875 and dynamic analysis should be done as per 8.3 of IS 6533.
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