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Re: FW: FW: R-values in Seismic Provisions

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>It would depend on the ratio of the mass to the stiffness (that stiffness
>contributing to the building stiffness).  If the non-structural elements had
>a higher mass to stiffness ratio than the structural elements, then the
>period would increase from the bare structural model.  The reverse would
>also be true.  In any event, as the non-structural elements degrade and lose
>stiffness (independant from other actions), the period of the structure
>would increase.  T=2*pi*Sqrt(W/gk).

Does this k in the equation includes non-structural element stiffness or no?

If not inculded ( which is usualy the case), then reduction of k due to loss
of stiffness contribution does not make sense to me.

If it is included (supposedly that we acurately added stiffness of
non-structural element and included them in k, lets call it k'), then loss
in stifness contribution, would reduce stiffness from k' to that of bare
frame, k.
So, in no circumstances behavior of non-structural elements stiffness would
cause the global stiffness to go lower than that of bare the frame, k, which
we usually use to calculate period. 

Please correct me if I am wrong.

Majid Sarraf

>Curt La Count
>Jacobs Engineering
>Portland, OR.
> ----------
>From: Majid Sarraf
>To: seaint(--nospam--at)
>Subject: RE: FW: R-values in Seismic Provisions
>Date: Wednesday, September 16, 1998 1:43PM
>With all due respect to Mr. Hamburger, I agree with Bill and I must add that
>Non-structural elemnts are indeed stiff but rather brittle elements that
>addiotional stiffness, by acting in parallel with the main structural frame.
>They must incerease the overal stiffness which results in decreased period
>(i.e. increased frequency) in the initial dynamic response, and later, as a
>result of failure of these non-structural elements or their stiffness
>degradation, overal stiffness reduces to that of the bare frame, and dynamic
>response corresponding to the period based on the bare frame stiffness
>should prevail.
>Please feel free to correct me on this.
>Majid Sarraf

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