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RE: SStud: Need opinions about residential construction andsteelstud shearwalls -Reply -Reply

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-----Original Message-----
From:	Tim McCormick [SMTP:TMCCORMI(--nospam--at)BAS.CI.LA.CA.US]
Sent:	Wednesday, December 03, 1997 10:22 AM
To:	seaoc(--nospam--at)
Subject:	Re: SStud: Need opinions about residential construction andsteelstud shearwalls -Reply -Reply


You raise the issue of stud buckling as the failure mode for structural
wood panel shear walls on metal framing. Does the APA report show
buckling at the wall ends? Can this be resolved by additional studs at the
wall end? If so, will this change the failure mode to the fasteners?

[Dennis S. Wish]  Tim, yes Table #4 in APA's Report #154 by John R. Tissell, PE which was dated May 1993 shows the mode of failure for each gauge stud and panel combination. With the exception of 14 gauge studs the mode of failure indicated was "studs buckled". The load factor (factor of safety determined by dividing the ultimate load by the target design shear) varied from 2.8 to 3.7 where the studs buckled.
However the text contains the following paragraph on page 9:
"Most of the walls tested failed prematurely when the end studs buckled or the bottom plate buckled at the buttress of the test fixture due to tearing of the bottom track at the anchor bolts. The tests did not provide a true indicator of the capacity of sheathing panels fastened to framing due to the weakness of the metal framing. Shear walls using metal framing require careful design of the end studs as highly loaded columns, and sufficient anchor bolts to provide for shear transfer from the bottom plate into the foundation or to the diaphragm supporting the wall."

Tim, in all fairness, I have not completed a review of LGSRG-3-96 - Shear Wall Values for Light Weight Steel Framing as prepared by Hoang Nguyen and Georgi Hall for the Project Director Reynaud Serrette for the Light Gauge Steel Research Group, Department of civil Engineering, Santa Clara University. Professor Serrette has been leading the way in his research on steel stud shearwalls and has been very active by his research sponsor - AISI as well as his association with the Light Gauge Steel Engineering Association. I suspect that it is this document which lead to the 1997 UBC provisions.

I will review the document and report back as to what changes have been achieved.

Dennis Wish PE