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RE: Inclined Diaphragms

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Yes, Eric, you answered my question.

Thank you very much

Alberto Guida

----- Mensaje original -----
De: T. Eric Gillham PE <gk2(--nospam--at)>
Para: seaoc list <seaint(--nospam--at)>
Enviado: miércoles 24 de noviembre de 1999 18:34
Asunto: Re: Inclined Diaphragms

> >Usually, existent software accepts only horizontal diaphragms. Which is
> reason of >this? and how  are considered the inclined diaphragms, for
> example, most of the roofs, in >the seismic analysis?
> >Thank you
> >Alberto Guida
> Alberto:
> Since you are asking about horizontal diaphragms, I am assuming that you
> dealing with rigid diaphragms (e.g. concrete slab/deck).  Most FEM
> does assume a horizontal rigid diaphragm, and this is adequate for many
> cases.  If you are modelling a roof diaphragm, with a slope for drainage,
> would think that assuming it was horizontal would be OK, since the slopes
> are typically less than 1/4" per foot.
> Now, if you are talking about a pitched roof, with say a 1:3 ratio, then
> assuming a rigid horizontal diaphragm would not be all that good of an
> You can still model it, though, using shell elements available though a
> general purpose FEM program such as SAP2000, RISA3D or (ugh) STAAD.  Just
> remember, though, that applying the inplane horizontal loading gets
> trickier, since you won't be able to apply the load (or displacement for
> that matter) at the centroid of the diaphragm.
> Does this answer your question?
> T. Eric Gillham PE
> GK2 Inc.
> PO Box 3207  Agana, Guam  96932
> Email - gk2(--nospam--at)
> Ph:  (671) 477-9224
> Fax: (671) 477-3456