Metal Deck Flexible Diaphragm with Cantilever
Metal Deck Flexible Diaphragm with Cantilever
(OP)
I have a 36 foot cantilever on a verco HSB-36, 20 gage roof deck. The depth is approximately 72' for a medical center here in Salem, OR. It is controlled by seismic design. The engineer I'm debating with on this says that the diaphragm is considered flexible under 12.3.1.1 of the ASCE 7-10. So far, I'm having a hard time fighting this one, but principles of mechanics don't seem to be properly addressed in the ASCE 7-10. The "a" dimension on the diaphragm doesn't seem to matter if under 200 ft if you look at page 6 0f 57 of the ER 2078P. I am a new plans examiner with 17 years of prior structural consulting experience. In my gut, I would design the roof deck as a rigid diaphragm and a flexible diaphragm and take the envelope solution for the horizontal distribution of forces as well as the collector design elements. Can anyone comment on the accuracy of just assuming simple tributary loading and neglecting the rotation?
In my opinion, I need to at least have him calculate the diaphragm flexibility to substantiate the design based on the esr report.
Thanks.
In my opinion, I need to at least have him calculate the diaphragm flexibility to substantiate the design based on the esr report.
Thanks.





RE: Metal Deck Flexible Diaphragm with Cantilever
RE: Metal Deck Flexible Diaphragm with Cantilever
An engineer may feel comfortable taking an envelope of rigid and flexible diaphragm results. When I am using software to analyze the lateral system and the diaphragm rigidity/flexibility is uncertain, I model the diaphragm stiffness rather than enveloping rigid and flexible.
RE: Metal Deck Flexible Diaphragm with Cantilever
Do you actually model the flutes and ribs and orientation of the diaphragm? Seems like modeling it would give you inaccurate results. I'm a big proponent of modeling what you actually have as FEA programs are only as intelligent as the user...
Thanks.
RE: Metal Deck Flexible Diaphragm with Cantilever
There is also a procedure outlined by Bentley that you could use as well:
http://communities.bentley.com/products/structural...
RE: Metal Deck Flexible Diaphragm with Cantilever