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RE: Basic Roof Diaph. Question

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Haan, Scott M POA wrote

" Also for z purlins you need to lay them out depending on the slope of the
roof: have adjacent purlin top flanges facing each other for a low slope
roof and purlin top flanges facing up slope for a high slope roof. "


I don't believe "need" is the case. It is preferable to have the top flange
pointing up the slope to minimise rotational instabilities of the section.
Whilst alternating orientation can minimise the tendency of the cladding and
purlins to roll-over. An effective bridging/bracing system is more reliable.
Bridging across the ridge of a doubly pitched roof also beneficial,
permitting weight of one side of the roof to balance the other.

Apparently it has been known for inappropriately braced roof cladding system
to rollover and crack concrete wall panels. And this is whether use z or c
purlins.

As you say however analysing cold-formed by hand can be "nasty".

Check out the following:

Assoc. Prof. Ben Schafer website at the John Hopkins University, CUFSM
software available for download to investigate the direct strength method of
assessing sections, and plenty of additional information available.

http://www.ce.jhu.edu/bschafer/

Also try CFS software for checking sections to the US code, the light
version is free but limits section to about five segments. Using steels
other than US steels is a bit cumbersome even with licensed version, but
other than that excellent program.

http://www.rsgsoftware.com/home.html


Regards
Conrad Harrison
B.Tech (mfg & mech), MIIE, gradTIEAust
mailto:sch.tectonic(--nospam--at)bigpond.com
Adelaide
South Australia




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