Maximum Diaphragm Dimension
Maximum Diaphragm Dimension
(OP)
IBC 2006 section 2305.2.3 gives ratios for maximum diaphragm dimensions for wooden structures.
Is there a maximum diaphragm dimension for a roof diaphragm with VERCO steel deck attached to reinforced concrete shear walls?
Thanks
Is there a maximum diaphragm dimension for a roof diaphragm with VERCO steel deck attached to reinforced concrete shear walls?
Thanks






RE: Maximum Diaphragm Dimension
DaveAtkins
RE: Maximum Diaphragm Dimension
RE: Maximum Diaphragm Dimension
Can the building grow in only one direction or two? This will depend upon brace locations and construction details.
Is the building heated, air conditioned or exposed to outside temperatures (ex. parking garage).
Types of construction: Prestressed, Post tensioned, conventional cast in place, steel, etc.
RE: Maximum Diaphragm Dimension
Mike McCann
MMC Engineering
RE: Maximum Diaphragm Dimension
RE: Maximum Diaphragm Dimension
One conversation that's been floating about my office is on these really large buildings, does a light gage steel deck really act like we think it will on such a large diaphragm? Not much testing at that scale. An option is to provide horizontal cross bracing in each direction instead of a diaphragm.
I've done several buildings with diaphragms that size and no expansion joint. We haven't had high winds or earthquakes yet to see how they perform. No complaints from the client though.
RE: Maximum Diaphragm Dimension
I'm performing a plan check review. I've used cross bracing as well as standard steel decking with diaphragm capacities. My original concern is that the columns, which are spaced at 50 ft OC each way are only gravity bearing. Typical designs I have used and seen on structures this large are cantilevered column designs, so they are taking up their portion of the seismic instead of perimeter walls taking all the seismic loading/reactions.
RE: Maximum Diaphragm Dimension
Plus, the diaphragm is much stiffer than the columns, so I doubt that the columns would ever be loaded to the degree calculated. You would have to calculate the stiffnesses based on relative deflections and back into the solution. The center columns would take more load than those closer to the walls too based on the deflection pattern of the diaphragm.
Mike McCann
MMC Engineering
RE: Maximum Diaphragm Dimension
Mike McCann
MMC Engineering
RE: Maximum Diaphragm Dimension
Thanks for the input! The structure is similar to a Super WalMart in design, except reinforcedd concrete walls instead of CMU walls.
Your comment: "That's a new one on me. I would never do it. It would drive up the required lateral force significantly." Are you saying you would or would not use cantilevered column design?
Thanks
RE: Maximum Diaphragm Dimension
If you are using unreinforce masonry limit your length to 200ft. Also for masonry the emperical approach limits the diaphragm width to length ratio to 2:1 per table 2109.2.1.2 FBC or IBC.
You said your walls are concrete. For tilt up construction the top of wall drift limitations are .005 x Height generally speaking though I don't think this is codified.
Mike I too would like to get the IBC reference for maximum length to width ratios for steel diaphragms. I have limited mine to a 2:1 ratio.
http://
John Southard, M.S., P.E.
http://www.pdhlibrary.com
RE: Maximum Diaphragm Dimension
Jon