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Drift per 1997 UBC

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Does anyone know why the drift check requires you to use the minimum base shear for buildings in Zone 4? What I'm talking about is UBC 1630.10.3 Limitations where it states that the limitations of equation (30-6) may be disregarded when checking drift. No mention is made of equation (30-7) which is the zone 4 minumum. There was no distinction in the 1994UBC based on zone.

This can greatly impact design for buildings with periods greater than 3 seconds in zone 4.

Any comments are appreciated.


Gerard Madden, P.E.
Civil Engineer

Middlebrook + Louie, Structural Engineers
71 Stevenson Street, Suite 2100
San Francisco, CA 94105
Tel: 415.546.4900
Fax: 415.974.3680
Email: gmadden(--nospam--at)