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.
Middlebrook + Louie, Structural Engineers
71 Stevenson Street, Suite 2100
San Francisco, CA 94105