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47.5 MB - The Whole Building Design Guide

47.5 MB - The Whole Building Design Guide

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Figure 3-117:Failed base flashingadhered directly to thebrick parapet. HurricaneKatrina (Louisiana, 2005)3.6.3 Exterior-Mounted EquipmentFastening rooftop equipment to curbs,as discussed in Section 3.3.4.1, is acost-effective approach to minimize windinducedproblems.Exterior-mounted equipment on existingcritical facilities should be carefully examinedand evaluated.3.6.3.1 Antenna (Communications Mast)Antenna collapse is very common. Besides loss of communications,collapsed masts can puncture roof membranes or causeother building damage as shown in Figure 3-118. This case alsodemonstrates the benefits of a high parapet. Although the roofstill experienced high winds that blew off this penthouse door, theparapet prevented the door from blowing off the roof.In hurricane-prone regions, it is recommended that antennaestrength be evaluated as part of the vulnerability assessment.Chapter 15 of ANSI/TIA-222-G provides guidance on the structuralevaluation of existing towers. Appendix J of that standardcontains checklists for maintenance and condition assessments.Additional bracing, guy-wires, or tower strengthening or replacementmay be needed.3-144 MAKING CRITICAL FACILITIES SAFE FROM High Wind

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