# RE: Design of RCC Dual Systems

• To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
• Subject: RE: Design of RCC Dual Systems
• From: "Yousefi, Ben" <Ben.Yousefi(--nospam--at)ci.sj.ca.us>
• Date: Mon, 7 Feb 2000 10:17:11 -0800
```The specific section in the 97 UBC is 1629.6.5 (pg. 2-12)

In regard to your modeling: your description of the model seems a bit
unusual. I don't know which program you are using, but most programs have
shear wall elements. So I am not sure why you have chosen beam-column
elements.

In regard to verifying the 25% rule. I would do a two-phase analysis/design:
1- First do the regular analysis with your design base shear and design the
shear wall.
2- From the output of your analysis determine what percentage of the base
shear is resisted by the frames. If less than 25%, artificially increase the
base shear to bring their portion to 25% and then proceed with the frame
design.

Hope it helps
Ben Yousefi, SE
San Jose, CA
-----Original Message-----
From:	satd(--nospam--at)techie.com [SMTP:satd(--nospam--at)techie.com]
Sent:	Monday, February 07, 2000 9:06 AM
To:	SEAOC
Cc:	satd(--nospam--at)techie.com
Subject:	Design of RCC Dual Systems

Hello everyone:

I am designing a reinforced concrete frame shear wall (dual) system
in Seismic Zone 4.  The frames are SMRFs.
I am using UBC-1997, FEMA-302 and ACI318 for design of these
systems.

For dual systems, FEMA 302 requires - "The moment frame must be
designed to have a capacity to resist at least 25% of the total required
lateral seismic force ..."

The system is 10 story tall with 3 equal bays.  The middle bay is
the shear wall and the outer two bays are SMRFs.  In other words, the frame
and the shear wall exist in the same vertical plane.  I have modelled the
shear wall using beam-column elements (i/c. shear deformation in the
analysis).  I have also modelled the thickness of the wall using rigid end
zones at the ends of the beams at each story level.  I have performed an
usual 2D-ELF analysis of the whole system.

How do I impose the 25% rule to the design of the SMRFs as required
by FEMA302?  Also, does this requirement exist in any particular section of
the UBC?

Any help and or suggestion in this regard will be appreciated.

Thanks,

Sat

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