Factory Mutual FM for Bar joist support.

[X4vier]

Hello,

Factory Mutual FM uses different assembly numbers for the roof with Bar joists as supports.
Does anybody know why bar joist assemblies are classified as separated from other Steel members?
Finally, they are concerned with the clip pulling out from the structural element - thickness is the only controlling factor.

 

[DanKile]

Two possibilities for bar joists being separated:
1) some panels got tested with cold formed solid web members and open web bar joists and had very different results
2) some panels use different clips for bar joists to anything else

For the clip screw pullout, when screwing in to thin material ( < 1/8" ) the thickness limits you to 1 to 2 threads of the screw. The thread failure is a function of material thickness. In thicker material, you'll want to check the screws tensile capacity.

 

[SandwichEngine]

FM not only charges somewhere near $10k to do a test to get one assembly rated, you also have to pay $10k per year to keep your product listed. Any tiny difference means they get to charge for a different assembly in perpetuity. FM is not your friend when it comes to using common sense or engineering to justify using anything that they haven't set up their protection racket for.