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[SEAOC] Re: [SEAOC] Plywood Shear Walls on Metal Studs and lightweight metal roof trusses

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The SEAOSC cyclic load test procedure (which is finalized but not officially
adopted as yet by the SEAOSC Board of Directors) is the only one like it in
the U.S. for framed wall assemblies (wood or steel framing). It is based on
a cyclic load test procedure recommended for masonry walls, developed in
1987 by a joint U.S.-Japanese structural/seismic engineering conference
(TCCMAR).   ATC 24 has a similar procedure for steel assemblies (not shear
walls), but it does not include some of the SEAOSC provisions. The City of
LA (COLA) Building & Safety Dept. asked SEAOSC to develop such a procedure
after the Northridge earthquake experience, and plans are to submit it to
COLA when officially adopted by SEAOSC.  Researchers in the U.S. (including
APA, UC- Irvine, Virginia Polytechnic Institute & State University and
Simpson Strong-Tie) are already using this procedure for preliminary studies
on shear walls, and a modified version of it is under consideration by ASTM
E6 for cyclic load testing of fasteners.  Until more cyclic load data is
available, the code recognized values can be used for design. COLA and the
County of LA have implemented an interim 25% reduction in shear values based
on monotonic tests, for seismic design (not wind design). This reduction
will be reconsidered again when cyclic load test data is available.  For
shear walls, both maximum shear strength (strength limit states) and
displacement (serviceability limit states) will be criteria that will be
considered, the latter to limit building damage.

As noted in other messages, there are shear values recognized by ICBO ES for
wood structural panel sheathing attached to steel framing for shear walls
and diaphragms (ICBO ES #4144 for Erico and #3447 for Pneutek), and another
manufacturer (Aerosmith) is/has submitted info to ICBO ES for a product
approval report.  Also, AISI is proposing shear wall values for this
application in the 1997 UBC (Code Change #240).  The info in APA Research
Report #154 can be used to support a specific design.

It appears to be necessary to "back up" end studs (chords) of shear walls
with back-to-back steel studs, to prevent buckling of the stud flanges.
Also, attachment of the top and bottom steel tracks (plates) need to be
reinforced at the connections with a plate washer to prevent
crippling/buckling  under lateral (sliding); and uplift forces on the tracks
must be avoided to prevent buckling of these components by using an
effective hold-down connector with low slip (such as Simpson Strong-Tie's
hold-down for steel framing).

John Rose/APA, Tacoma, WA
___

>I previously reported that a SEAOSC Ad-Hoc committee was issuing a draft
>for cyclic testing of metal stud walls. This was not quite correct. I
>received a copy of the current draft this afternoon and provide the
>following Scope of work as noted on the report. Please note that this is a
>procedure only - for the cyclic testing of any framed wall system - not
>limited to wood and steel stud. The report is a current draft only. To
>obtain a copy, I suggest you contact SEA of Southern California and request
>the following title dated January 18, 1996 (11 pages total):
>
>
>"Standard Method of Cyclic (Reversed) Load Test for Shear Resistance of
>Framed Walls for Buildings
>Based upon ASTM Standard E 564-76 (Reapproved 1984)
>
>1. Scope
>1.1 This method is designed to evaluate the shear stiffness and shear
>strength of a typical section of a framed wall system, including its shear
>connections and hold-down connectors, under cyclic (reversed) load
>conditions. 
>1.2 This method may involve hazardous materials, operations, and equipment.
>This method does not purport to address all of the safety problems
>associated with its use. It is the responsibility of whomever uses this
>standard to consult and establish appropriate safety and health practices
>and determine the applicability of regulatory limitations prior to use."
>
>Essentially, this is a proposal for establishing testing criteria for any
>framed shearwall system. Once established and accepted, this criteria can
>be used to obtain working stress values for various shearwall systems
>including steel stud and wood frame.
>
>What I interpret from this is that there is no conclusive standard for the
>evaluation of shear wall systems under cyclic (seismic) load. Although the
>values published by ICBO appear to be the most current allowable stress
>which we are allowed to use, these are applicable to wood framed systems
>only.
>
>Once the Ad-hoc committee report is approved, appropriate testing can be
>done by the AISI and other interested proprietary suppliers to determine
>allowable values for each system.
>
>Finally, it appears to me that there are really two choices at the present
>for the design of plywood shear panels on steel stud. That is:
>1. Use the values provided by APA under the research report #154 (John R.
>Tissell, Structural Panel Shear Walls, APA Tacoma Washington, May 1993) for
>wind governed loads only.
>2. Disallow the use of steel studs with plywood sheathing for designs
>governed by seismic. The steel stud system may be able to be designed as a
>braced framed system rather than accounting for the capacity of plywood and
>screws.
>3. Design for alternative shearwall elements.
>
>Does this sound reasonable, or is there any other information out there?
>
>Finally, are there any standards for the manufacturing of lightweight metal
>roof trusses to be used on steel stud walls. These would be trusses spaced
>at 24" on center. 
>
>You comments are greatly appreciated.
>Sincerely
>Dennis S. Wish PE
>
>...
>
>
>

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