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RE: Drift per 1997 UBC

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Personally, I am glad the minimum base shear per eqn. 30-7 was kept. Having
no minimum base shear for calculating the drift is a dangerous proposition
in high seismic areas. Many structures are drift controlled and if you
calculate the period by method B you may get a substantially large period
for these buildings, and you may end up designing the building for a drift
based on a small fraction of base shear that you design the elements for. In
my humble opinion, ignoring the 30% limitation on period calculation is
enough of a break

Ben Yousefi, SE
San Jose, CA

	-----Original Message-----
	From:	Gerard Madden [SMTP:GMadden(--nospam--at)mplusl.com]
	Sent:	Friday, February 02, 2001 12:50 PM
	To:	seaint(--nospam--at)seaint.org
	Subject:	Drift per 1997 UBC

	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

	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)mplusl.com