Transferring Horizontal Shear Through Joist Seat at Concrete-Filled Metal Deck Diaphragm

[abusementpark]

I've been reviewing different articles and resources regarding the use of joist seat rollover to transfer horizontal forces in joist-framed floors and roofs. On page 35 of the Designing With Vulcraft publication (linked below), it indicates that if sidelap fasteners are required, then a drag strut or other shear transfer device "would likely be required", and joist rollover could not be used. I can see the logic of that for a bare metal roof deck, since the number of sidelap fasteners appears to be directly related to diaphragm shear capacity.

However, for a concrete-filled non-composite metal deck, the sidelap fasteners make very little difference in shear capacity. Take for example a Vulcraft 1.0C 26 gage metal deck with #12 support fasteners, #10 sidelap fasteners, and a deck of 3 feet. The 0 sidelap fastener diaphragm capacity with a 33/4 support pattern is 1160 plf. However, increasing the number of sidelaps to 5 only ups the capacity to 1357 plf. I am thinking that the logic about transferring the horizontal shear through joist seat rollover cannot apply to concrete-filled metal deck diaphragms, since the concrete strength factors into the diaphragm strength, but not the shear transfer. Thoughts?

How do you normally prove the load transfer path in this scenario?

https://www.vulcraft.com/upload/cat...STEEL-JOISTS-JOIST-GIRDERS-AND-STEEL-DECK.pdf

 

[XR250]

I believe the boundary conditions are still governed by the perimeter fastening and conditions. The shear still needs to have a path OUT of the concrete diaphragm. I would call out some 2 1/2" tube steel between joists and use that for boundary fastening that can resist the design shear.

 

[SteelPE]

Did you look at page 147?

I don’t remember the last time I used a collector as shown on page 35. The are a pain to get right in the field.

I haven’t used shear collectors in a while, but if I ever use them on concrete floors (4” slab of .6c deck) I usually weld shear studs to them.

 

[txeng91]

The ideal situation for using the rollover capacity would be at a deck/slab edge where the edge angle would collect the load from the diaphragm and transfer it to the joist seat through the welds. It’s only practical for relatively low shears (<400 plf) but you can get around having to put tubes between the joists like XR250 mentioned.