THE BUILDING ENVELOPE: Lecture 6

Analysis of Debris Loads

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

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)

DEBRIS IMPACT PROVISIONSIN ASCE 7-02

• Hurricane prone regions

• Wind borne debris regions

• Glazing, impact resistant

• Impact resistant covering

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

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

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

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

GLAZED OPENING DESIGNS

FOR WINDBORNE DEBRIS

TYPICAL GLAZING SYSTEM DESIGNS THAT MEET IMPACT STANDARD

TYPICAL GLAZING SYSTEM DESIGNS THAT MEET IMPACT STANDARD

TYPICAL GLAZING SYSTEM DESIGNS THAT MEET IMPACT STANDARD

TYPICAL GLAZING SYSTEM DESIGNS THAT MEET IMPACT STANDARD

TYPICAL GLAZING SYSTEM DESIGNS THAT MEET IMPACT STANDARD

SHUTTER SYSTEMS THAT MEET IMPACT STANDARD

SHUTTER SYSTEMS THAT MEET IMPACT STANDARD

PRODUCT APPROVALS

• Dade County (Florida) Office of Code Compliance

• Texas Department of Insurance

• ICC Product Evaluations

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