Effect of reinforcing on UL fire ratings

[danhahn]

A composite slab design for a hospital in California has been reinforced for diaphragm forces using #4 at 16 e/w. The UL design quoted (D916) called for 6x6/10x10 mesh. The design replaced the mesh with the rebar. The fire marshal says this design does not meet the UL requirement because the rebar is diferent than the mesh. Does anyone have a reputable source that adresses the effect of reinforcing on fire ratings?? UL is no help, they want to thicken the slab by the difference in reinforment diameters???

 

[Focht3]

I think you're stuck thickening the slab or reverting to the mesh (yuck!). The issue is thermal conductivity, not structural equivalence. Steel conducts heat much better than concrete does -



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[jheidt2543]

To meet the UL rating, you must provide exactly the same detail that was tested. However, I do seem to remember that there are calculation methods that can be used to figure out the fire rating that can be assigned to the slab. I would contact either NFPA, ACI or PCA (or all three) and find out the details on the method.

BUT, if it is a UL rating you MUST have, then you are stuck with meeting the EXACT requirements of the UL rating.

After some of the tragic fires around the country this summer, I can see why the Fire Marshal's are getting picky.