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RE: Cap Beam Shear Wall System

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The shearwall design procedure in UBC 1921.6.6.5.2 is for a shearwall hinging at the base.  The cap beam may itself form a hinge and so you may need to use the procedure mentioned in 1921.6.6.5.1.
 
I don't think the cap beam necessarily needs to remain elastic.  If it forms a plastic hinge it must be detailed appropriately. 
 

Eric Lehmkuhl,  S.E.
KPFF Consulting Engineers, San Diego
(619) 521 8500 phone
(619) 521 8591 fax
eric.lehmkuhl(--nospam--at)kpff.com

-----Original Message-----
From: Michael Bryson [mailto:MBryson(--nospam--at)mhpse.com]
Sent: Wednesday, January 23, 2002 4:51 PM
To: 'seaint(--nospam--at)seaint.org'
Subject: RE: Cap Beam Shear Wall System

Thanks for your reply. Can you elaborate on what you mean by your last sentence?
 
I do think you need to design the cap beam to remain elastic i.e. design it for omega0 or for the capacity of the walls.
 
 -----Original Message-----
From: Eric Lehmkuhl [mailto:eric_lehmkuhl(--nospam--at)kpff.com]
Sent: Wednesday, January 23, 2002 12:02 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: Cap Beam Shear Wall System

I recently designed a concrete shearwall that is outriggered with story high beams to perimeter gravity columns at mid-height of the building.  This has some similarities to your situation.  I did a typical dynamic analysis and a pushover which was helpful.  One thing I would watch out for - the "joint" shear where the coupling beam intersects the wall.  These shears may be very high.  Is the bottom flange of the coupling beam braced by a slab?  Also, the typical displacement design for concrete shearwalls (in the UBC) must be modified to account for more than one plastic hinge.
 

Eric Lehmkuhl,  S.E.
KPFF Consulting Engineers, San Diego
(619) 521 8500 phone
(619) 521 8591 fax
eric.lehmkuhl(--nospam--at)kpff.com

-----Original Message-----
From: Michael Bryson [mailto:MBryson(--nospam--at)mhpse.com]
Sent: Monday, January 21, 2002 4:45 PM
To: 'seaint(--nospam--at)seaint.org'
Subject: Cap Beam Shear Wall System

Anybody have any opinions about a Cap Beam concrete shear wall system?
 
I am reviewing an 18 story building that has a 6ft deep beam at the roof that couples the walls. The result is that there are two plastic hinges, one at the roof level and one at the ground level.