wind drift criteria

huangyhg

wind drift criteria
i have a general question regarding the inter-storey drift. i am talking relative to nbcc95 and i am sure there would be a similar clause in other building codes. as we know that this is l/500 for the 10 year return period for serviceabilty.
to check this l/500 should we add the effect for torsional component of wind action or just simple orthagonal(wx orwy)wind. torsional component is similar as we introduce 10% eccentricity for eq.
please clarify me. thanks or your help.