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RE: Drift per 1997 UBC

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Shocks! I was hoping that is not a mistake and that someone in his right
mind decided to keep 30-7 as a minimum.

	-----Original Message-----
	From:	Mike Valley [SMTP:mtv(--nospam--at)skilling.com]
	Sent:	Friday, February 02, 2001 1:43 PM
	To:	seaint(--nospam--at)seaint.org
	Subject:	RE: Drift per 1997 UBC

	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