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Re: R value for the design of braced frame in a plywood shear wall building

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The issue is whether or not the bracing system is "required" to support
gravity loads.  The gravity system must be cable of maintaining function
even if inelastic behavior / energy dissipation occurs in the brace.  For
example, a typical chevron frame may be designed where the beam is capable
of supporting the gravity loads even if the bracing was removed, or the beam
may be sized with reliance on support from the bracing for vertical
integrity.  In both cases the braces will carry gravity load in the braces
prior to inelastic behavior.


Paul Feather PE, SE
pfeather(--nospam--at)SE-Solutions.net
www.SE-Solutions.net
----- Original Message -----
From: "Alexander Sasha Itsekson" <sasha(--nospam--at)engstruc.com>
To: <seaint(--nospam--at)seaint.org>
Sent: Wednesday, August 14, 2002 9:03 AM
Subject: R value for the design of braced frame in a plywood shear wall
building


> Paul,
>
> Thank you for your response.  I have to agree that the arrangement I
> described is not a dual system even though I do have a plywood shear wall
in
> the same line of resisitance that just didn't have enough capacity to
resist
> seimic loads but will add some redundancy to this line of lateral
> resistance. But this is not the point.
>
> How can you detail a X-braced frame that where braces do not carry any
> gravity loads?
>
> Most of  gravity loads will go into columns, but some (proportioned to
> stiffness of brace+connections vs column) will get to braces as well.  Am
I
> missing something?  Slotted bolted connection will not work as the
> connection will not be able to carry lateral loads. If this is the case,
can
> the R=5.5 be used at all in this situation?
>
> Regards,
>
>
> Alexander (Sasha) Itsekson, SE
> Enginious Structures
> Oakland, CA
> tel. 510.601.1646
> fax  510.420.8110
>
>
____________________________________________________________________________
> _____________
> From: "Paul Feather" <pfeather(--nospam--at)SE-Solutions.net>
> To: <seaint(--nospam--at)seaint.org>
> Subject: Re: R value for the design of braced frame in a plywood shear
wall
> building
>
> This is a multi-part message in MIME format.
>
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>
> Depends on your brace configuration.
>
> You do not have a "dual" system.  Transitioning to a single frame line =
> somewhere in a structure does not qualify as a dual system.  If the =
> building is essentially a wood bearing wall / shearwall system, the =
> appropriate R factor would be 5.5 (less than three stories).  If the =
> braced frame element is not configured in such a way that the braces =
> carry gravity load, the same 5.5 factor would apply for the braced frame =
> per 1630.4.2, 1630.4.3, and 1630.4.4.
>
> If the bracing does in fact carry gravity load, then the R value of 4.4 =
> would apply to the entire structure, including the wood shear walls =
> under the same code sections.
>
>
> Paul Feather PE, SE
> pfeather(--nospam--at)SE-Solutions.net
> www.SE-Solutions.net
>   ----- Original Message -----=20
>   From: Alexander Sasha Itsekson=20
>   To: seaint(--nospam--at)seaint.org=20
>   Sent: Tuesday, August 13, 2002 8:03 AM
>   Subject: R value for the design of braced frame in a plywood shear =
> wall building
>
>
>   Hi,
>
>   Should I be using R of 4.4 for an X- braced frame at the first story =
> and for all of the plywood shear walls in the direction of the braced =
> frame including the ply shear wall above the braced frame?
>
>   I originally used R=3D5.6 (item 2.4.a of table 16N of the UBC) because =
> braces are not designed to support gravity loads.  The plan checker =
> commented that the use of R=3D4.4 is appropriate per item 1.4.a because =
> this is a bearing wall building.  In fact I believe that this is a dual =
> system building where part of it is a bearing wall and other part is a =
> building frame system (steel columns and beams at the line where the =
> brace frame occurs).
>
>   Any thoughts?
>
>   Regards,
>   Alexander (Sasha) Itsekson, SE
>   Enginious Structures
>   Oakland, CA
>   tel. 510.601.1646
>   fax  510.420.8110=
>
>
>
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