Drag coefficients and shear performance of metal roofing for building diaphragm loading

[fastline12]

Trying to finalize some numbers for wind protection of a building. I need to account for diaphragm action of the building to better estimate wind load ratings. I am looking for any standards or help in determining the proper drag coefficient to use here and how I might account for the shear performance of the corrugated metal roofing that will be applied to the walls and roof. Ultimately, I need to drive this back to building standards for final approval.

The roofing is a 26ga PBR ribbed.

 

[hokie66]

For some reason, I didn't think fastline was talking about farm buildings. Maybe his "Aerospace" area of interest led me to think aircraft hangar.

 

[Brad805]

I think he is talking about a personal project he is making some sort of glulams for.

I have seen these pole buildings up to 60'x300'. They started as farm bldgs, but you see them pop up in commercial locations where the building inspectors are lax. Personally, I think the designers of the ones in my neck of the woods do not consider lateral loads at all.

 

[fastline12]

Maybe I can explain more to see if you guys can offer some design ideas? The building is for personal use, not commercial or aerospace related.

General design minimums per code are 20psf live roof, 10psf dead roof, 75mph cont wind, 90mph gust. Dimensions are 60x96x17 with 3:12 pitch free span, 12ft bay spacing. This presents a unique challenge in the custom roof trusses but I think we have our load in order on the trusses. The design calls for all girts/perlins to be installed in joist hangers, purlins are 2x8 SPF on 24" centers, girts are 2x6 on 36" centers. 26ga PBR roof paneling installed on walls and roof. Main columns are 5 ply 2x8 glulam, embedded 4ft, concrete floor.

Without applying diaphragm action, the columns are undersized but we know from experience in the area that lesser buildings survive here in the midwest.

Technically, we could probably sign off the building to meet the minimums but are looking at further improvements that will increase survivability at high wind ratings. It is inevitable that the structure will see 100+ MPH. We are trying to determine proper drag of the paneling to better estimate loading. We may also install blocking to better handle the shear.

There is to be a wall all the way across the building at the 36ft mark. We have yet to determine if we will need shear capacity in that wall. It is intended to be drywalled on both sides.


There are some lengthy studies available from universities that indeed prove shear ability through the roof panels but we want to stay conservative with that. One element I personally am trying to avoid which is stitching screws which connect the 3ft panel widths. They are not very attractive but do increase shear handling.

 

[DaveAtkins]

There are various ways to justify lateral loads on these buildings:

Design the columns as cantilevers (usually won't work).

Design the columns and trusses as moment frames (usually will require knee braces).

Design the roof as a diaphragm, and the side walls as shear walls (this is the way I have typically done it).

You could also use that interior wall as a shear wall, but it would need to be connected to the underside of the roof diaphragm (alternatively, a drag truss could be positioned over the wall).

DaveAtkins

 

[fastline12]

Dave, just as a general, I am curious, are you typically able to validate the roof paneling over the purlins as a sufficient diaphragm?

Also, to throw a wrench here, I was desiring a "reverse" rolling PBR panel on the walls which, if not familiar, is the exact same panel form, just flipped over so the fasteners are in the valleys. I can see some structural concerns with that but I assume you would typically need blocking on the ends for shear anyway? This would also create an air gap between the frame and panels which may or may not be a good thing. I would like to think I can get some worth while convection cooling behind there but that will probably just introduce dirt into the wall system.