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[mc.upadhyay1]

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.


Regards

Mukesh Upadhyay

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