Transferring diaphragm shears through purlins sitting on beams
Transferring diaphragm shears through purlins sitting on beams
(OP)
I'm wondering if it's possible to transfer diaphragm flange forces through purlins running perpendicular to the flange beam sitting on it (sorry if this is confusing, I've attached a sketch). My concerns are:
1 - this is a torque on the purlins
2 - purlins are spaced at 5', is this too great?
3 - connector strength, this required contribution of several connectors on the purlins to safely resist load.
I've see a design that welded HSS to the eaves to avoid transferring shear through joist seats before, but purlins are stronger than joist seats.
More misc info - 30'widex40'longx10'tall building, W16x26 purlins on W16x35 beams. Very low seismic, wind loads
~30 psf net in one direction. Haven't done much roof diaphragm design outside of cookie cutter stuff, it's atypical in the industrial sector I work in
1 - this is a torque on the purlins
2 - purlins are spaced at 5', is this too great?
3 - connector strength, this required contribution of several connectors on the purlins to safely resist load.
I've see a design that welded HSS to the eaves to avoid transferring shear through joist seats before, but purlins are stronger than joist seats.
More misc info - 30'widex40'longx10'tall building, W16x26 purlins on W16x35 beams. Very low seismic, wind loads
~30 psf net in one direction. Haven't done much roof diaphragm design outside of cookie cutter stuff, it's atypical in the industrial sector I work in






RE: Transferring diaphragm shears through purlins sitting on beams
Why do you need to do this? Is the lower beam a drag strut?
Mike McCann, PE, SE (WA)
RE: Transferring diaphragm shears through purlins sitting on beams
RE: Transferring diaphragm shears through purlins sitting on beams
RE: Transferring diaphragm shears through purlins sitting on beams
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.
RE: Transferring diaphragm shears through purlins sitting on beams
RE: Transferring diaphragm shears through purlins sitting on beams
I'd think that the stiffeners would be cheaper than in plane roof bracing or the HSS shear lugs. The stiffeners can be shop installed and you should easily be able to get by with one-sided, partial height stiffeners.
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.
RE: Transferring diaphragm shears through purlins sitting on beams
RE: Transferring diaphragm shears through purlins sitting on beams
Mike McCann, PE, SE (WA)
RE: Transferring diaphragm shears through purlins sitting on beams
Another option could be to upset your purlins 6" or so and cantilever out with a channel or HSS. This would get you back to a more conventional rollover height and wouldn't require field welding.
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.
RE: Transferring diaphragm shears through purlins sitting on beams