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Re: Steel SMRF on Conc. shearwall

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Gerard:

No the steel SMRF is not sitting on a collector.

It's sitting directly on the top of the Conc. Shearwall.

The steel collector connects to the top of the SMRF at frames' beam level and it's inline with it.

I hope this clarifies.


Regards
Casey (Khashayar) Hemmatyar
Private email <k(--nospam--at)hemmatyar.com >
California
==========================================

From: Gerard Madden, SE [mailto: gmse4603(--nospam--at)gmail.com]
Sent: Wednesday, February 21, 2007 8:42 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: Steel SMRF on Conc. shearwall

 

What do you mean the SMRF is connected to a steel collector? It's pretty common if not unusual if there is no collector to DELIVER load to the SMRF. Are you saying that the SMRF sits on a collector which then takes the load to the concrete shearwall that's left/right of the steel frame? Maybe if you clarify the situation, we can figure out why the plan checker is making you design the thing as a discontinuous system. Plan and Vertical Irregularities don't trigger Omega level forces (there are other penalties/additional work to do) but discontinuities will do that.

-g

Experienced SE for a plan checker is generally good, but that doesn't always translate to correctness. Maybe I'm not understanding the question/description.

On 2/21/07, Casey K. Hemmatyar <khemmatyar(--nospam--at)gmail.com > wrote:

Gerard and  David:

 

Thanks for kind responses.

The plan check engineer, which is an experienced SE, has indicated that both steel SMRF and Conc. shearwall to be designed for Em.

On my first email to the SEAINT Listserve, I did not mention that the SMRF is connected to a Steel Collector which brings about 60% of it's total seismic load.

Do you believe that the SMRF should not be designed for Em?

If SMRF does not need to be designed by Em then the Conc. shearwall qualifies for "Vertical Combination" per 1630.4.2. and does not need to be designed for Em either.

Thanks in advance

Casey (Khashayar) Hemmatyar
Private email <k(--nospam--at)hemmatyar.com>
California

================

Casey,

Wouldn't this qualify as a "Vertical Combination"?  See CBC 1630.4.2 
David A. Topete, SE

Structural Engineer

GFDS Engineers

543 Howard St., First Floor

San Francisco, CA 94105

v : (415) 512-1301 x21

f : (415) 512-1302

dtopete(--nospam--at)gfdseng.com

www.gfdseng.

==============

It's not discontinuous.

What you do is design the portion above the shearwall using the appropriate R factor. Then you get your reactions from the above structure, scale them by the relative Rtop/Rbot ratios and design the lower portion using the R for the lower system.

It's like treated them as two separate structures where you transfer the reactions from above to below.

It's not a soft story or anything like a vertical irregularity. In tall structures it's something to monitor and examine the combined stiffness effects and drift issues.

-gm