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RE: Drift per 1997 UBC

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ICBO issued an erratum on January 18, 2001 (which has not yet been
published) which changes this section to read as follows:
"1630.10.3 Limitations.  The design lateral forces used to determine
the calculated drift may disregard the limitations of Formula (30-6)
and (30-7) and may be based on the period determined from Formula
(30-10) neglecting the 30 or 40 percent limitations of Section
1630.2.2, Item 2."

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Michael Valley, P.E., S.E.                   E-mail: mtv(--nospam--at)skilling.com
Skilling Ward Magnusson Barkshire Inc.              Tel:(206)292-1200
1301 Fifth Ave, #3200,  Seattle  WA 98101-2699      Fax:        -1201

-----Original Message-----
From: Gerard Madden [mailto: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