How do I determine the fire rating or resistance of hollowcore plank? Should I specify a UL Rating?
Like all precast, prestressed concrete products, hollowcore slabs have excellent fire resistance. Depending on thickness and strand cover, ratings up to a 4-hour endurance can be achieved. A fire rating is dependent on equivalent thickness for heat transmission, cover over the prestressing strand for strength in a high temperature condition and end restraint. Underwriters Laboratory (UL) publishes fire ratings for various assemblies. The fire ratings should be considered in determining the slab thickness to be used in preliminary design. A typical 8-inch thick hollowcore plank has a 2-hour fire rating. For a higher rating (3- or 4- hour), typically a concrete (or gypsum based) topping would be applied or a spray-on fire resistant material can be added to the underside of the plank. This is also shown in the UL directory. Model codes like the IBC have prescriptive fire ratings. This is the best way to indicate ways to accomplish specified fire ratings and should be the first choice. UL
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