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RE: frame drift

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Paul,

It depends on how you detail the connections of the metal studs to the
steel frame. You can either allow the "cladding" to accommodate the
drift by allowing it to rotate/hinge as the building moves or it sounds
like you are trying to design the studs to withstand the drifts in
bending.

I think you should think of the cladding as a rigid body and allow it a
path to move either in the joints of the cladding system or via the
connections to the steel frame. Isolate the systems.

If the metals studs were bearing/shear elements, what you are proposing
would make sense to me, but l/480 seems okay to me. It gets back to what
is your objective, save lives or prevent unsightly cracks.

Hth,
-gerard
Santa Clara, CA

-----Original Message-----
From: PFFEI(--nospam--at)aol.com [mailto:PFFEI(--nospam--at)aol.com] 
Sent: Wednesday, November 06, 2002 7:31 AM
To: seaint(--nospam--at)seaint.org
Subject: frame drift

i have a condition with a building with a 4" stone veneer on metal stud 
backup in seismic zone 4.  in the majority of areas, there is enough
solid 
wall that i can utilize braced frames as the lateral force resisting
system 
to control building drift.  

however, on some elevations of the building, the layout of the windows
and 
wall openings is such that braced frames are not feasible, and i need to
use 
moment frames.  (the mass of the building is way beyond limits of
plywood 
shear walls and concrete or masonry shear walls in these elevations is
not an 
option). the code specified drift seems excessive for a building with
this 
type of brittle veneer. (results in "delta s" of l/480 deflection if
consider 
R as 8.5 or even greater if i consider the braced frames in the
building). 
veneer ties have some capacity to allow lateral deflection.  what would
a 
reasonable drift limit be to damage in the veneer. i am inclined to use
l/600 
max delta deflection based on code limits for support of stone, masonry
and 
other veneer.

thanks in advance -

paul franceschi s.e.

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