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Posted by Tasha Weiss on October 10, 2013 at 3:47 PM.
Two successful full-scale fire tests conducted by AISI and AISC at Underwriters Laboratories (UL) 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 in. of normal weight concrete over steel deck supported by a W-shape beam. The first test was conducted in January and ran for two hours and 32 minutes before the loading mechanism reached its limit. The second test was held in March and ran for two 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.
More information on the tests is available in an article from the September 2013 issue of MSC, “Restrained or Unrestrained?” by Charles J. Carter, S.E., P.E., Ph.D.; and Farid Alfawakhiri, P.ENG., Ph.D.
“Simply stated, these test results are great,” said Carter. “They provide a solution that eliminates the need to argue about what fire protection thickness is required. Now, if you decide to use a restrained rating or one of these unrestrained ratings, you will get the same fire protection thickness.”