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RE: FW: R-values in Seismic Provisions

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I think it depends on what a non-structural element is, infill masonary
walls, for example, which are not traken into account in lateral stiffness
of the frames, can increase the stiffness of the frame in initial response,
once they crack they lose their stiffness contribution, and become like
other masses on the frame, with a difference that they can dissipate some
energy too.

Initial increased stiffness (reduced period) can indeed intensify the
initial response and induce high demand in the frame than it was originally
designed for. It is indeed very logical to separate the infills from
structure to avoid this negative effect of stiffness increase. Of course the
brittle walls would damage and disspiate energy through friction, etc... but
this happens at a later stage in dynamic response. This somewhat depends on
the frequency content and nature of damging pulses too. If the most damaging
puls occurs first , it would not be of much use to have non-strucural
elements disspiating energy and reducing demands, as the pick response has
passed (i.e too late for help, damage is done!). When the sever shaking
happens at a later stage though, and after that walls crack, then
disspiation of energy + stiffness of the bare frame is would alliviate the
response and reduce the demands in the frame. However, we can not predict
the nature of the shaking, so why taking any chances.

Just another humble one,

Majid Sarraf


>>If the non-structural elements had
>>a higher mass to stiffness ratio than the structural elements,
>Not to beat this completely bloody, but their individual stiffness 
>doesn't matter as much as their ability to contribute to the overall 
>energy of deformation. To the extent that they just ride along with the 
>rest of the structure without being a part of the overall load path, 
>non-structural elements just add mass. 






>
>Christopher Wright P.E.    |"They couldn't hit an elephant from
>chrisw(--nospam--at)skypoint.com        | this distance"   (last words of Gen.
>___________________________| John Sedgwick, Spotsylvania 1864)
>http://www.skypoint.com/~chrisw
>
>
>
>
>

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