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Gypsum sheathed shear walls

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As I go deeper into the IBC 2000, I am finding more and more interesting
things!  I have a building which was originally designed per the 1996 BOCA
building code.  I am now redesigning the building for the IBC 2000.

I know that the trend is to avoid the use of gypsum sheathed shear walls,
but many residential builders prefer them at interior locations for obvious
reasons since most interior  load bearing wood frame walls require 5/8" Type
X gypsum wall board for fire ratings.  In chapter 23 (WOOD) values are given
for capacities of gypsum sheathed shear walls.

If the structure you are designing does not conform to the provisions of
Section 2308 "CONVENTIONAL LIGHT-FRAME CONSTRUCTION" (no specific seismic
analysis required) or you can not use the simplified analysis provisions of
Section 1617.5 (diaphragms of wood structural panels are permitted to be
considered flexible for horizontal force distribution and story drift can be
taken as 1% of the story height unless a more exact analysis is provided)
you can not use gypsum sheathed shear walls.

The reason I say can not is that in FEMA 303 (Part 2 - Commentary - 1997
NEHRP Provisions for Seismic Regulations for New Buildings and Other
Structures) states the following: "The capacity of shear walls shall be
determined either from tabulated values that are based on experimental
results or from standard principles of mechanics.  The tables of allowable
values for shear walls sheathed with other than wood or wood-based
structural use panels were eliminated in the 1991 provisions {I think they
mean 1994 provisions} as a result of re-learning the lessons from past
earthquakes and testing on the performance of structures sheathed with these
materials during the Northridge Earthquake..........One stipulation is that
there are no accepted rational methods for calculating deflections for
diaphragms and shear walls that are sheathed with materials other than
wood-based structural-use panel products fastened with nails.  Therefore, if
a rational method is to be used, the capacity of the fastener in the
sheathing material must be validated by acceptable test procedures employing
cyclic forces or displacements.  Validation must include correlation between
the overall stiffness and capacity predicted by principles of mechanics and
that observed from test results."

Does anyone know if any testing has been done on gypsum wallboard (GWB)
sheathed shear walls?

I know that many buildings have been constructed with GWB shear walls, even
in California.  What approach are others using in this situation, tell the
client "you can no longer do what you have been doing for the past "XXX"
years?

How have you approached clients with this issue?

Any other comments or insights?

Thanks in advance for your responses.

Albert J. Meyer, Jr., P.E.
Senior Project Engineer
Cagley, Harman and Associates
Structural Engineers / Parking Consultants
1015 West Ninth Avenue
King of Prussia PA 19406-1222
ameyer(--nospam--at)cagleyharman.com
(610) 337-3360
(610) 337-3359 Fax
www.cagleyharman.com


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