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RE: Dual System - SCBF w/SMRF

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I would put in my 2 cents about why IMHO this is a superior system:

The main advantage is drift control. Much of the damage to SMRF's in
Northridge could possibly have been avoided if a dual system was used rather
than only SMRF's. The large displacement demands on the connection is
probably one of the major causes of the connection failures. As far as I
know no damage was reported to the connections in any buildings that
utilized dual system (although that might be because there were no such
buildings in that area!). 

In a dual system the SMRF is a backup to the braced frame and it is only
required to resist a minimum of 25% of the total load. However, there is no
limitation on the height of a building that uses this system, whereas for
braced frame only, there are such limitations.

As far as the distribution of loads it is basically distributed in
accordance to the rigidity of the lateral force resisting elements (hence a
rigid type diaphragms is required for such system). Usually a 3D analysis is
performed for evaluating the response of such buildings.

Ben Yousefi, SE
San Jose, CA

	-----Original Message-----
	From:	Eddie Gonzalez [SMTP:Eagonzal(--nospam--at)ENG.CI.LA.CA.US]
	Sent:	Friday, November 12, 1999 8:05 AM
	To:	seaint(--nospam--at)
	Subject:	Dual System - SCBF w/SMRF

	The Code seems to allow one to used a dual system composed of SBCB
w/ SMRF. 
	Has anyone ever used such an animal.  If so,
	Q1: What does it usually look like - perimeter frames with braced
core, or
	adjacent SMRF in same brace line or even both a SMRF and SBCB in the
same bay. 
	That last version would seem to be a connection nightmare.
	Q2: Do you have difficulty evaluating the overall response, being
that one
	system is usually much stiffer than the other?
	Q3: Why might one seek to used this - - architectural restrictions?

	Ed Gonzalez

	p.s. The SEAOSC seminar on SCBF by the AISC-LA Chapter was very
insightful and
	packed full of information. If anyone did not get to go, you should
try to get
	the notes from SEAOSC.