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Calculate Equivalent Mechanical Fastener Attachment to 5/8" Puddle Weld at 8 Inch On Center

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TylerM94

Structural
Jun 2, 2020
26
Looking for a gut check to confirm an equivalent mechanical fastener attachment pattern to using 5/8" puddle welds at 8 inches on center. The situation I have is connecting new metal deck to existing metal deck. I came up with #10 screws at 3 inches on center is equivalent to 5/8" puddle welds at 8 inches on center.

Metal Deck: Vulcraft 3NL-32, 18 Gage (t=0.0474 in), Fy = 50 ksi, Fu = 65 ksi, G60 Galvanized Sheet.
Check Deck in Tension:
Pn = 0.7*t*da*Fu = 0.7*0.0474*0.5302 (Type B Double Thickness of Sheet)*65 ksi = 1,143 lbs
Using a #10 screw with 18 gage base metal, the SDI deck table I consulted provides a tensile capacity of Pn = 473 lbs. Solving for the equivalent spacing I get 3.3 inches.

Check Deck in Shear:
Pn = 0.88*t*da*Fu
Pn = 0.88*0.0474*0.5302*65 = 1,437.5 lbs

Using a #10 screw with 18 gage base metal, the SDI deck table I consulted provides a shear capacity of Pn = 789 lbs. Solving for the equivalent spacing I get 4 inches.

Tension controls in this case. Does it seem reasonable that an equivalent to 5/8" puddle welds at 8 inches on center is #10 screws at 3 inches on center? This seems like very close spacing to me.
 
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Have a look at the Vulcraft website. They have tools for diaphragm design. You can try various arrangements and compare to get equivalent capacities out of different fasteners.
 
Any diaphragm shear implications? If so, you may want to look at diaphragm stiffness when using mechanical fasteners. due to the increased fastener slip, the stiffness is often notably lower even if the strength calculations work out.
 
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