Alternate steel diaphragm design
Alternate steel diaphragm design
(OP)
I have a project where the contractor did not puddle weld the steel roof deck to the bar joists with 5/8" puddle welds. The deck was just spot welded to the joists with a MIG welder from below. It was not noted by the inspector until after the roof had been completely constructed. I have talked to the deck supplier and SDI and they have never heard of anyone fastening the deck from the bottom and basically said the design tables would not apply to fastening from the bottom of deck. Has anyone ever ran into this situation before?
I looked at some type of screw/rivet system that would be equivalent to a #12 screw and provide compression from the top of the deck similar to a screw from the top. The contractor is concerned with the amount of predrilling that would be needed.
Could you neglect the deck and transfer the load with structural steel between the bar joists? What would be the most efficient and cost effective way to transfer the load? I would appreciate any input.
I looked at some type of screw/rivet system that would be equivalent to a #12 screw and provide compression from the top of the deck similar to a screw from the top. The contractor is concerned with the amount of predrilling that would be needed.
Could you neglect the deck and transfer the load with structural steel between the bar joists? What would be the most efficient and cost effective way to transfer the load? I would appreciate any input.






RE: Alternate steel diaphragm design
RE: Alternate steel diaphragm design
RE: Alternate steel diaphragm design
I'd also be worried that the deck welds would be insufficient for uplift and the smaller amount of shear capacity required to brace the joist top chords and transfer seismic inertial forces out of the roof and into the joists. QC on those overhead welds might be a problem.
As StructSU10 noted, you can use a discrete bracing system so long as a complete load path is provided. That's no small thing however. Among other difficulties, some of your joists will likely become axially loaded members. Vulcraft has a manual that deals with this although not with your specific situation: Link
If you install bracing across the entire roof, I imagine that you'll be stuck having to do something below your joists which is tricky. Depending on what your framing looks like, you may be able to scale your fix back to just smaller horizontal trusses around the perimeter of the building.
A colleague of mine did something related, albeit on a much smaller scale. She installed new drag struts into an existing roof. Hilti helped us work out a system for fastening below the deck. The issue seemed to be whether or not you could install the fasteners from the underside without simply pushing the deck away from the drag strut rather than piercing the deck and engaging it properly.
We ended up using hot rolled channels for the drag struts. Overhanging cold formed sheets were fastened to the channels on the ground. Once the channels were lifted into place, the last step was to screw the cold formed sheets into the deck. The thinking was that a CFM to CFM connection would be more successful than a hot rolled steel to CFM connection would be. I'm not sure if that's true but one advantage of this system was that it was pretty easy to verify the results.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Alternate steel diaphragm design
You have the diaphragm shear and uplift loadings so you might be the best to come up with a solution -
or you could put the monkey on their back and ask them to hire an engineer to solve - with your cooperation in providing required loads, etc. and demanding a PE produce calculations backing up any solution.
I've attached a sketch similar to what KootK suggested - only using all light gage and fabricating a large number of bent clips with screw fasteners.
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RE: Alternate steel diaphragm design
I was thinking about using Fab Lok fasteners. See the link below. The diameter would be larger than a #12 screw. Is it reasonable to consider it as an equivalent to a #12 screw and use the diaphragm values for #12 screws? Maybe it makes the most sense to use a combination of X-bracing and fasteners to achieve all of the design requirements. Thoughts?
http://www.elcoconstruction.com/Products/Metal-Fas...
RE: Alternate steel diaphragm design
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Alternate steel diaphragm design
There is insulation between the metal deck and roof membrane so I don't see any issues with penetrating the roof membrane.
Is it reasonable to use the Fab Lok fasteners as an equivalent to #12 screws?
RE: Alternate steel diaphragm design
RE: Alternate steel diaphragm design
Unlikely it will ever get done correctly from below.
Why would they have done overhead welds from below when doing it from above is so much easier?
RE: Alternate steel diaphragm design
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Alternate steel diaphragm design
RE: Alternate steel diaphragm design
RE: Alternate steel diaphragm design
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Alternate steel diaphragm design
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Alternate steel diaphragm design