Analysis of Irregular Shaped Structures (Diaphragms)

[Simba13]

Good Afternoon all,

I'm working on an analysis of a concrete diaphragm with multiple large openings. I'll admit that as a junior engineer my knowledge of diaphragms is pretty much limited to the simple examples required to pass the PE. I've leafed through Malone and Rice's "Analysis of Irregular Shaped Structures" and beyond being a bit difficult to digest (for my monkey brain ) I have no idea how much of these examples apply since the book is pretty much exclusively looking at wood/flexible diaphragms. So how do you all approach analyzing rigid diaphragms with multiple large openings? I'm not looking to be spoon-fed, even just some simple bullet points on steps would be incredibly helpful. Also, is there a comparable reference to M & R's book but for rigid diaphragms? The closest I found was one of the examples out of SEAOC vol 3 but even that one only had 2 shears walls on each edge (I have 4 in the N-S dir.).

 

[driftLimiter]

NEHRP For cast in place. Can also apply to c.o. mtl deck diaphragms.

This is a very comprehensive guide with additional references.

Reg' your diaphragms dynamic behavior it looks like it will have alot of torsion so make sure you address that early on in your thought process.

 

[Simba13]

Yeah, should have mentioned that NEHRP was my first stop, but so much of it was focused on seismic and this building is in SDC A.

 

[driftLimiter]

Well, load path is load path. Sure there are many seismic provisions but you need to address diaphragm shear, chord forces, openings, diaphragm deflection.

 

[sticksandtriangles]

As far as practical, lets get this done advice, do you have this diaphragm in a piece of software like RAM or ETABs?
If so, I would go ahead and model in the estimated stiffness of the diaphragm, making it a semi-rigid diaphragm, and try to take section cuts through your diaphragm to see what forces are acting on your at areas of interest.

One note, at the locations adjacent to large openings, be sure to include both moment and axial force with designing chords and collectors.

In the example above, what I have typically done to design the rightmost chord element is take the moment, divided by the depth of the "sub diaphragm" and then add it the axial load divided by 2. This is some rough engineering and math, but I think this is standard of care for diaphragm design from the information that I have gathered.

S&T -

http://www.re-tug.com