huangyhg

ibc 2003 - table 1604.3
in ibc 2003 - table 1604.3, note f states "the wind load is permitted to be taken as .7 times the "component and cladding" loads for the purpose of determining deflection limits herein."
anyone know the origin of this note? is it similar to the serviceability for drift information in asce?
thanks.

rc
all that is necessary for the triumph of evil is that good men do nothing.
edmund burke

check out this thread:
thanks for the information, but the note in ibc only states for components and cladding, where that thread was discussing drift limits of mwfrs.
any ideas on why this is limited to c+c?
rc
all that is necessary for the triumph of evil is that good men do nothing.
edmund burke

could it be that the reason for the 0.7 (per the linked threads) is that it is based on the statistical differences of the wind pressures that only really affect the peak pressures that c&c are so susceptible to?...while the mwfrs wind is more of a global averaging of the wind over larger areas and thus not affected to any degree by the difference in the statistical wind measurements?

i used 0.7w for checking serviceability drifts of mwrs all the time - the code does not explicitly cover wind drifts and thus it is left up to engineering judgement.
there is a return period factor in the commentary of asce 7. typically as willisv pointed out, drifts are checked for a 10 year return period storm while strength design is done at a 50 year return period. the factor for a 10 year return period is around 0.7.
i agree with willis. we use 0.7w for checking drifts all the time. i don't think this in inappropriate. first, it accounts for the 10-year return period (though, admittedly, i do use 0.71 for v=90mps, and a different - slightly higher - factor for higher velocities); second, if you want to get technical, the mwfrs and c&c wind loads are the same if the trib area is >750ft2, as would be the case for the whole building when checking drift.

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