openings on roof deck

[CecileRod]

We need to make some openings on a metal roof deck (1970, 18ga, 1.5"B). What is the effect of these new openings on the deck in terms of strength decrease? I read in an old catalog that openings cannot sum up to more than 0.5% of the entire deck area, but I haven't read that anywhere else.

 

[PAstructural08]

I would frame the opening out with channels or angles and attach the decking to those members (bolts, screws, welds, etc..). If you do that than the opening could be as large as required.

 

[jayrod12]

How big of openings and how many?

 

[KootK]

I think our standard detail indicates that nothing needs to be done for openings 18" square and smaller. Above that, we require CFM/hot rolled angle/channels to frame out the perimeter for gravity loads. Even with the framing, there will be a limit beyond which deck diaphragm capacity would be impacted in a meaningful way and one would need to start viewing the edge support framing as collector elements transferring force around the opening (often collectors need to extend beyond the opening).

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.