47.5 MB - The Whole Building Design Guide

that includes discussion on air retarders. Air retarders can beeffective in reducing membrane flutter, in addition to being beneficialfor use in ballasted single-ply systems. When a mechanicallyattached system is specified, careful coordination with the structuralengineer in selecting deck type and thickness is important.If a steel deck is selected, it is critical to specify that the membranefasteners be attached in rows perpendicular to the steel flangesto avoid overstressing the attachment of the deck to the deck supportstructure. At the school shown in Figure 3-59, the fastenerrows of the mechanically attached single-ply membrane ran parallelto the top flange of the steel deck. The deck fasteners wereoverstressed and a portion of the deck blew off and the membraneprogressively tore. At another building, shown in Figure 3-60, themembrane fastener rows also ran parallel to the top flange of thesteel deck. When membrane fasteners run parallel to the flange,the flange with membrane fasteners essentially carries all the upliftload because of the deck’s inability to transfer any significantload to adjacent flanges. Hence, at the joists shown in Figure 3-60,the deck fasteners on either side of the flange with the membranefasteners are the only connections to the joist that are carryingsubstantial uplift load.Figure 3-59:The orientation of themembrane fastener rowsled to blow-off of the steeldeck. Hurricane Marilyn(U.S. Virgin Islands, 1995)3-74 MAKING CRITICAL FACILITIES SAFE FROM High Wind