47.5 MB - The Whole Building Design Guide

ASTM E 1996 specifies five missile categories, A through E. The missiles are of various weightsand fired at various velocities during testing. Building type (critical or non-critical) and basicwind speed determine the missiles required for testing. Of the five missiles, the E missile hasthe greatest momentum. Missile E is required for critical facilities located where the basic windspeed is greater than or equal to 130 mph. Missile D is permitted where the basic wind speed isless than130 mph. FEMA 361 also specifies a missile for shelters. The shelter missile has muchgreater momentum than the D and E missiles, as shown below:Missile Missile Weight Impact Speed MomentumASTM E 1996—D9 pound 2x4 lumber50 feet per second(34 mph)14 lb f-s*ASTM E 1996—E9 pound 2x4 lumber80 feet per second(55 mph)22 lb f-s*FEMA 361 (Shelter Missile)15 pound 2x4 lumber147 feet per second(100 mph)68 lb f-s**lb f-s = pounds force per second3.4.3.2 Windows and SkylightsExterior glazing that is not impact-resistant (such as laminatedglass or polycarbonate) or protected by shutters is extremely susceptibleto breaking if struck by wind-borne debris. Even small,low-momentum missiles can easily break glazing that is not protected(see Figures 3-84 and 3-85). At the hospital shown inFigure 3-84, approximately 400 windows were broken. Most ofthe breakage was caused by wind-blown aggregate from the hospital’saggregate ballasted single-ply membrane roofs, and aggregatefrom built-up roofs. With broken windows, a substantial amount ofwater can be blown into a building, and the internal air pressurecan be greatly increased (as discussed in Section 3.1.3) which maydamage the interior partitions and ceilings.MAKING CRITICAL FACILITIES SAFE FROM High Wind3-103