Vijaya- Brian Carlisle already responded with regard to wind drifts. For seismic, drifts are computed per ASCE 7-10 Section 12.8.6. The drift of concern is that due to seismic alone (not in combination with other loads). Seismic drifts are computed using the horizontal forces associated with the base shear force V, computed in accordance with the ELF or RSA procedures without further modification or load factors.
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Ronald Hamburger, SE
Consulting Principal
Simpson Gumpertz & Heger
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