47.5 MB - The Whole Building Design Guide

Figure 3-9:Aggregate blow-offassociated with buildingirregularities. HurricaneHugo (South Carolina,1989)Figure 3-10 shows a stair tower at a hospitalInformation pertaining to load calculationsthat caused turbulence resulting in windis presented in Section 3.3.1.2. For furtherspeed-up. The speed-up increased the suctionpressure on the base flashing along thegeneral information on the nature ofwind and wind-building interactions, seeparapet behind the stair tower. The builtuproof’s base flashing was pulled out fromBuildings at Risk: Wind Design Basics forPracticing Architects, American Institute ofunderneath the coping because its attachmentwas insufficient to resist the suctionArchitects, 1997.pressure. The base flashing failure propagatedand caused a large area of the roofmembrane to lift and peel. Some of the wall covering on thestair tower was also blown away. Had the stair tower not existed,the built-up roof would likely not have been damaged. To avoiddamage in the vicinity of building irregularities, attention needsto be given to the attachment of building elements located inturbulent flow areas.To avoid the roof membrane damage shown in Figure 3-10, itwould be prudent to use corner uplift loads in lieu of perimeteruplift loads in the vicinity of the stair tower, as illustrated inFigure 3-11. Wind load increases due to building irregularitiescan be identified by wind tunnel studies; however, wind tunnelstudies are rarely performed for critical facilities. Therefore,identification of wind load increases due to building irregu-3-16 MAKING CRITICAL FACILITIES SAFE FROM High Wind