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RE: Gypsum sheathed shear walls

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I don't think there is any specific item listed that prohibits it, but if I
can't calculate deflection of a shearwall by a rational means without
testing, then technically I can't calculate story drift.  If I can't
calculate drift how do I know I meet the code criteria?  It seems reasonable
to assume that in most cases that there would be more flexibility in GWB
shear walls than that of wood structural panel shear walls, implying a rigid
diaphragm, but if I don't have the ability to compare the stiffness of the
walls to the diaphragm I can't really determine whether the diaphragm is
flexible or rigid (as defined per IBC 2000).  Without knowing stiffnesses
how do I know the force distribution?  Do I simply look at both cases (rigid
and flexible) and envelope the solution?  I don't want to be overly
conservative but I'm trying to improve my approach and also meet the code
requirements as best I can.  Thanks for your input.

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


-----Original Message-----
From: Scott Maxwell [mailto:smaxwell(--nospam--at)engin.umich.edu]
Sent: Thursday, September 05, 2002 12:02 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Gypsum sheathed shear walls


Albert,

Just a note...is there anything in the 2000 IBC that prohibits the use of
gypsum sheathed shear walls (assuming that conventional construction or
the simplified design are not used) or is the only "prohibition" that you
found in FEMA 303, but  not in 2000 IBC?

The reason that I ask is that the FEMA documents don't have any real
"force" (other than standard of care type "force") unless it is a
governement project, and even then there is some "wiggle" room.  The
reason is that the FEMA/NEHRP documents are NOT written as code documents
(i.e. use mandatory language).  That is why the 2000 IBC and other codes
cannot just reference the NEHRP provisions.  The NEHRP provisions must be
first "converted" into code speak and then included in the codes.

Now, I am not saying that the recommendations or provisions in the NEHRP
should be ignored...just pointing out that you might be reading a little
too much of the NEHRP provisions into the 2000 IBC.  Just want to make
sure that you basing the perceived "prohibition" on what is actually in
the IBC.

HTH,

Scott
Ypsilanti, MI


On Thu, 5 Sep 2002, Al Meyer wrote:

> 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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