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47.5 MB - The Whole Building Design Guide

47.5 MB - The Whole Building Design Guide

47.5 MB - The Whole Building Design Guide

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Fan cowling attachment: Fans are frequentlyTo avoid corrosion-induced failure (seeblown off their curbs because they are poorlyFigure 3-78), it is recommended thatattached. When fans are well attached, theexterior-mounted mechanical, electrical,cowlings frequently blow off (see Figureand communications equipment be3-70). Blown off cowlings can tear roof membranesand break glazing. Unless the fanmade of nonferrous metals, stainlesssteel, or steel with minimum G-90 hot-dipmanufacturer specifically engineered thegalvanized coating for the equipmentcowling attachment to resist the design windbody, stands, anchors, and fasteners.load, cable tie-downs (see Figure 3-71) areWhen equipment with enhanced corrosionrecommended to avoid cowling blow-off.protection is not available, the designerFor fan cowlings less than 4 feet in diameter,1 / 8-inch diameter stainless steel cablesshould advise the building owner thatperiodic equipment maintenance andare recommended. For larger cowlings, useinspection is particularly important to3/ 16-inch diameter cables. When the basicavoid advanced corrosion and subsequentwind speed is 120 mph or less, specify two cables.Where the basic wind speed is greaterequipment damage during a windstorm.than 120 mph, specify four cables. To minimizeleakage potential at the anchor point,it is recommended that the cables be adequately anchored tothe equipment curb (rather than anchored to the roof deck).<strong>The</strong> attachment of the curb itself also needs to be designed andspecified.Figure 3-70:Cowlings blew off twoof the fans on a policebuilding that housed thecounty’s EOC. HurricaneIvan (Florida, 2004)MAKING CRITICAL FACILITIES SAFE FROM High Wind3-85

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