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RE: SEISMIC FORCE -DISCONTINUITY

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Agreed, except I would add "or the shear wall itself" if in fact it is the weakest link in the chain.
 
One simple analogy is to think of the overall system as a chain composed of links representing the various mechanisms for the various components of the system.  In this situation, one element could be represented by more than one link - for example, a cantilevered R/C wall would have two links - one for shear (diagonal tension) failure, one for flexural yielding.  A frame might have many links - flexural yielding in beams, shear failure in beams, flexural yielding in columns etc.
 
The design process consists of identifiying all of the possible links and categorizing them.  For an R/C frame, shear failure is NOT a viable mechanism since it does not allow for sustained yieldings that can dissipate energy effectively over many cycles (as opposed to steel elements that COULD handle diagonal tension yielding)..  Flexural yielding in beams, however, is recognized as viable for R/C beams given proper detailing.
 
Anyway, those links that represent yield or failure mechanisms that are to be avoided must be made stronger than those links representing "good" yield mechanisms.  The chain MUST experience yielding, but it is the designer who determines where this yielding will occur - in the viable mechanism links and NOT in the "failure" links.  Once this has been accomplished, the elastic analysis that most codes let us use for seismic design ceases to be of value, since the relative strengths of the various links controls.  It needs to be remembered that inelastic action is assumed by the codes for the design earthquake, it is our job to design and detail the buildings such that it must yield in a stable manner that will allow for energy dissipation to occur over many cycles.
 
Regards,
 
Tiger
 

Terangue *Tiger* Gillham, PE
GK2, Inc.
PO Box 8061, Koror, Palau 96940
Phone: (680) 488-7282 office
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tiger(--nospam--at)palaunet.com <mailto:tiger(--nospam--at)palaunet.com>

-----Original Message-----
From: Tom.Hunt(--nospam--at)fluor.com [mailto:Tom.Hunt(--nospam--at)fluor.com]
Sent: Thursday, May 18, 2006 5:08 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: SEISMIC FORCE -DISCONTINUITY


Eliseo,

Anything in the lateral force resisting system/frame that contains your shear wall that has a capacity less than the shear wall.

Thomas Hunt, S.E.
Fluor



Eliseo Arellano <eliseoas(--nospam--at)earthlink.net>
05/17/2006 09:46 AM
Please respond to seaint
To
seaint(--nospam--at)seaint.org
cc
seaint(--nospam--at)seaint.org
Subject
SEISMIC FORCE -DISCONTINUITY






Hello


Could comment on a simmilar cituation. A shear wall supported by beam. What would be the maximum force deliver by the system to the beam?. Thanks

Eliseo Arellano

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