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RE: Flat Plate in Seismic Zone 4

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I agree with Harold.  Some plan checkers may give you problems with the
higher R, though.  Some have asked for proof that the gravity system will be
intact if the shearwalls have lost all load bearing capability.  Deformation
compatibility under the 1997 UBC will definitely provide challenges not only
in the gravity column design, but also for slab punching shear.  Also, the
1997 UBC forces you to detail heavily loaded concrete columns like moment
frames no matter what the drift induced seismic moments on the column are.
Eric Lehmkuhl,  S.E.
KPFF Consulting Engineers, San Diego

-----Original Message-----
From: Sprague, Harold O. [mailto:SpragueHO(--nospam--at)]
Sent: Tuesday, May 09, 2000 11:24 AM
To: seaint(--nospam--at)
Subject: RE: Flat Plate in Seismic Zone 4

Obviously you are using the 1997 UBC.

You should be meeting the intent of the code.  Don't forget the deformation
compatibility using the 3*Rw/8 and the P-delta effect on the columns.

Harold Sprague

> -----Original Message-----
> From:	M. A. Mufti [SMTP:mam(--nospam--at)]
> Sent:	Wednesday, April 26, 2000 11:08 AM
> To:	seaint(--nospam--at)
> Subject:	Flat Plate in Seismic Zone 4
> I am designing a building in seismic zone 4. The architect has proposed
> a flat plate structure on rc columns with concrete shear walls.
> Of course, dual system is out of the question as UBC and ACI do not
> allow
> flat plate as a lateral force resisting system in zone 4. Can we design
> the structure as a Building Frame System with Rw=8 with shear walls
> taking 100% of seismic force and designing the flat plate system for
> gravity loads and seismic moments induced by deformation compatibility.
> This frame will be designed as Ordinary Moment Resisting Frame without
> detailing for ductility.
> If the above works out well, does it fulfil the intent of the code?
> M. A. Mufti