Semi-Rigid Diaphragm

[CBEngi]

Hello,

I have an extremely large industrial building. with purlins running at 2.4 m c/c, continuous over all beams/girders. the purlins are about 12" deep with a metal decking on top.

My question is how can I determine if the purlins are capable of transferring the load to and from the decking into my LLRS or should I not consider it a diaphragm to the building at all with such a high purlin offset?

Thanks in advance.

 

[KootK]

I do love a discrete horizontal bracing system for this kind of structure. But economy is king.

A large building does not necessarily mean large unit diaphragm shears. And those unit shears are just eccentric axial loads on your purlins which can be designed for. Moreover, the purlins themselves may not need to take any of the unit diaphragm shears. If need be, you could use hot rolled perimeter steel for that purpose.

The only concern that I'd have with the 12" purlins is if you're attempting to resist shear at the purlin ends via rollover. Collector elements / shear lugs may be a better choice there.

If you post a plan framing sketch, we'll be happy to review it and provide comment.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[CBEngi]

Perfect! thanks a lot for the help KootK.