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THE BUILDING ENVELOPE: Lecture 6
Analysis of Debris Loads
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DEBRIS LOADS: PHYSICS
Large Missiles:
Timbers, roof tiles, sheet metal, bricks
Fly or tumble near ground
Impact speed 1/3 to 1/2 of V
Small Missiles:
Roof gravel, glass particles,
Fly at rooftop elevations
Impact speed 90% of V
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ASTM STANDARD E1886-02(TEST METHOD)
• Large missile: 4.5 - 15 lb 2x4 timber impacting between 0.10 and 0.55 of the
basic wind speed (3-sec gust)
• Small missile: solid steel ball having a mass of 2 gm impacting between 0.40 and 0.75 of the basic wind speed (3-sec gust)
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DEBRIS IMPACT PROVISIONSIN ASCE 7-02
• Hurricane prone regions
• Wind borne debris regions
• Glazing, impact resistant
• Impact resistant covering
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ASTM STANDARD E1996- 02 (SPECIFICATION)
Level ofProtection
EnhancedProtection(essentialfacilities)
Basic Protection Unprotected
AssemblyHeight
30 ft > 30 ft 30 ft > 30 ft 30 ft > 30 ft
Wind Zone 1 D D C A None None
Wind Zone 2 D D C A None None
Wind Zone 3 E D D A None None
Wind Zone 4 E D D A None None
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IMPACT TEST PROTOCOL
• Impact with representative missile–large missile (2x4 timber)–small missile (2 gm steel ball or rock)
• Apply fluctuating pressures–inward acting–outward acting
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FLUCTUATING PRESSURES IN U.S. CODES AND STANDARDS
Inward Acting Pressure Outward Acting Pressure
Range Numberof cycles
Range Numberof cycles
0.2PMAX/0.5 PMAX 3,500 0.3PMAX /1.0 PMAX 50
0.0 PMAX /0.6 PMAX 300 0.5 PMAX/0.8 PMAX 1,050
0.5 PMAX/0.8 PMAX 600 0.0 PMAX/0.6 PMAX 50
0.3 PMAX/1.0 PMAX 100 0.2 PMAX/0.5 PMAX 3,350
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U.S. CODES AND STANDARDS WITH DEBRIS IMPACT PROVISIONS
• ASCE 7-02• International Building Code• International Residential Code• Florida Building Code • TWIA Building Code• ASTM E1886/1996
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GLAZED OPENING DESIGNS
FOR WINDBORNE DEBRIS
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TYPICAL GLAZING SYSTEM DESIGNS THAT MEET IMPACT STANDARD
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TYPICAL GLAZING SYSTEM DESIGNS THAT MEET IMPACT STANDARD
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TYPICAL GLAZING SYSTEM DESIGNS THAT MEET IMPACT STANDARD
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TYPICAL GLAZING SYSTEM DESIGNS THAT MEET IMPACT STANDARD
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TYPICAL GLAZING SYSTEM DESIGNS THAT MEET IMPACT STANDARD
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SHUTTER SYSTEMS THAT MEET IMPACT STANDARD
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SHUTTER SYSTEMS THAT MEET IMPACT STANDARD
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PRODUCT APPROVALS
• Dade County (Florida) Office of Code Compliance
• Texas Department of Insurance
• ICC Product Evaluations
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WINDBORNE DEBRIS: RISK MODEL
Facility Design Windspeed (3 sec gust, mph)
Design Missile Impact Speed(ft/sec)
Hospital, FL 140 9 lb 2x4 timber 50
Cruise Line HQ, FL 174 9 lb 2x4 timber 50
Legal Office, Caribbean 156 15 lb 2x4 timber 66
University Med. Ctr., FL 174 15 lb 2x4 timber 73
Regional Med. Ctr., GA 155 15 lb 2x4 timber 65