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RE: Exposed Beam Roof Design (fwd)

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Dennis:

If you really think about it there should be little concern about a clay
tile roof being "tossed" off a SIP roof.

Clay tile roofs weigh about 20 psf max (at least per weights in the AISC
manuals...those manuals actually say 14 psf...so I tossed you a little
extra to 20 psf).  Let's say that an earthquake causes a lateral interia
force on the tiles of 5 times that of gravity (this should be WAY
conservative...for heavy roof top units, others were talking a max of 4
times).  That is a lateral force of 100 psf.  Covert that to psi and you
get about 0.7 psi.  This would in effect be that lateral shear force
applied to the top skin of the SIP panel and thus, the shear force in the
EPS foam.  EPS foam has significantly greater shear capacity than 0.7 psi.
There is literature out there with values (one that I found with Google
had a value of 31 psi for 1 lb density foam, but I will admit that I am
not fully sure of accuracy, but that seems about right from what I
recall...the other value for say compression that this document had
"tracks").  But, even if you don't believe the values in literature, then
you could back calculate a shear in the foam from panel load span tables
and a transformed section analysis of the composite SIP panel.

Beyond all that, one could potentially argue that the SIP foam layer could
actually act kind of dampening layer much like elastomeric/rubberized
based isolation dampeners that have been used in some situations.  But, I
definitely don't know of any testing to support this idea.

Regards,

Scott
Adrian, MI


On Fri, 23 Jun 2006, Dennis Wish wrote:

> Chuck,
> It still comes down to how the shank of the connector will perform (bending)
> and any displacement (laterally) that will toss the heavy clay tile off the
> roof.
> 7-1/2" is not bad, but we need at least a 2x10 for BATT Insulation here in
> the Mojave Desert for control of the energy calculations. Beyond this, we
> also need a way to get the HVAC through, over or around the Heavy Timbers
> unless there is enough room to bring it through the sides of the 38-foot
> room. Going above, while not meeting the thin edge look that the Architect
> created is the best choice for running electrical and mechanical through the
> framing.
>
> Best Regards,
> Dennis
>

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