Two successful full-scale fire tests conducted by the American Iron and Steel Institute and the American Institute of Steel Construction at Underwriters Laboratories provide insight for construction professionals struggling to decide whether to specify restrained or unrestrained fire protection thicknesses for structural steel-framed buildings. The answer is that the required fire protection will be the same, at least for the floor construction described in the new U.L. Design No. D982.
AISI and AISC conducted tests of two unrestrained structural steel-framed floor specimens with 4.5” of normal weight concrete over steel deck supported by a W-shape beam. The first test was conducted on January 8, 2013 and ran for 2 hours and 32 minutes before the loading mechanism reached its limit. The second test was held on March 13, 2013 and ran for 2 hours and 29 minutes before the limit was reached. Both tests exceeded expectations.
“Based on tests that the steel industry conducted 30 years ago and on empirical observations made since then, we have always advocated that restrained ratings are applicable for the vast majority of structural steel-framed building designs,” said Robert Wills, P.E., vice president, Construction Market Development for the Steel Market Development Institute, a business unit of AISI. “These new tests give the steel industry the opportunity to update the state of fire science and document for a new generation of architects, engineers and code officials that steel-framed buildings can be designed with fire protection thicknesses that are both safe and cost-effective.”
The new UL Design No. D982 provides for two-hour unrestrained assembly ratings with unprotected steel deck and SFRM (Spray-Applied Fire-Resistive Materials) protection on the steel beam with thickness sufficient to obtain a one-hour unrestrained beam (temperature-based) rating.