# RE: Modeling Diaphragm Stiffness of Unreinforced Masonry

• To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
• Subject: RE: Modeling Diaphragm Stiffness of Unreinforced Masonry
• From: Ing. Arturo Martínez <amartine(--nospam--at)udep.edu.pe>
• Date: Fri, 30 Apr 1999 13:45:04 -0500
```Rodrigo:
Once you obtain results from the structural analysis, i.e. axial force in the X-brace, do you use the horizontal component of this force to check shear in-plane stresses on the wall?
I doubt this may work, at least for low h/l ratios.

Arturo

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De:     	Rodrigo Lema[SMTP:rlema(--nospam--at)arnet.com.ar]
Enviado: 	Martes 27 de Abril de 1999 1:28 PM
Para:   	seaint
Asunto:     	RE: Modeling Diaphragm Stiffness of Unreinforced Masonry

Yes, by structural element I mean the adjacent concrete framing member.  Sorry I translate literally.  A little history; we use a lot and I mean a LOT of concrete and very few steel.  It's a problem of relative costs.  So, by the time the code was written, the authors intended to generalize the concepts, and that's why it reads "structural element" instead of just plain "concrete".
And "x-brace", it was the term I was seeking until I decided to explain it as "inclined prop".  And, you are right, you have to model it as a compression only member.
The expression for A comes from (I once verified it) taking into account the shear in-plane stiffness the infill adds to the frame.  Of course, it's an elastic approach (which I think is suitable for your wind problem), but for seismic design purposes it's ok too given the uncertainties present once you look at the whole picture.
BTW, when I mentioned Paulay & Priestley's book, It was "Seismic design of reinforced concrete and masonry buildings", by John Wiley & sons.  But back then, I haven't yet noticed that seismic loads were not your main concern.

Rodrigo Lema.
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