THE BUILDING ENVELOPE: Lecture 1 EFFECTS OF HURRICANES on THE BUILDING ENVELOPE Presentation format: This lecture will be most effectively presented using Power Point projection in the classroom as there are many color photographs. Alternate presentation: print slides and notes as handouts. COURSE INTRODUCTION In introducing the course the instructor should state that where buildings and hurricanes are concerned the building envelope is the most important part of the structure. If the building envelope is breached financial loss can be unacceptable, even if the principal structural frame survives. The objectives of the course are: (1) to establish the importance of the building envelope to the satisfactory performance of buildings in hurricanes, (2) to define the building envelope for design purposes, (3) to describe methods of design for the building envelope, including procedures for going “beyond the code” when circumstances warrant, and (4) to illustrate, through examples, modern designs of typical building envelope systems. LECTURE INTRODUCTION The objective of Lecture 1 is to illustrate the performance of the building envelope in hurricanes. This objective is accomplished by defining important meteorological aspects of hurricanes and illustrating hurricane caused damage to buildings, emphasizing the performance of the building envelope. INSTRUCTOR NOTES

HURRICANE METEOROLOGY Hurricanes are discussed elsewhere in the textbook. A summary of important meteorological aspects of hurricanes that are important to building design is included here. Meteorological aspects of hurricanes of engineering importance: Severe tropical cyclone, typhoon, and hurricane are the same meteorological event. Large atmospheric vortex, dozens to hundreds of miles in diameter Calm eye, ten to tens of miles in diameter Winds spiral inward toward eye. Rain bands contain thunderstorms with severe turbulence. General references on hurricanes: Riehl (1959); Dunn and Miller (1960); Simpson and Riehl (1981); Pielke and Pielke, 2000) The Building Envelope INSTRUCTOR NOTES

HURRICANE WIND FIELD The Building Envelope Understanding the hurricane wind field is important to appreciating the effects of hurricanes on buildings. General flow is inclined 15-20 degrees from a tangent to a circle Building at A will experience winds changing from North to Southeast as the hurricane moves West. If translation speed is 20 mph and the diameter of hurricane force winds is 50 miles, building at Point A will be affected by hurricane force winds for 2 1/2 hours. Several devastating hurricanes were slow-moving (< 5 mph): Cyclone Tracy (Australia, 1974) Hurricane Marilyn (US Virgin Islands, 1995) Hurricane Mitch (Honduras, 1998) The Building Envelope INSTRUCTOR NOTES

WIND GUSTS The Building Envelope Wind gusts are a part of the wind load formulation found in building codes and standards. Thousands of gusts can affect a building. While only one is a ‘peak’ gust, many near the peak will affect a building. Largest winds are also the most turbulent (Krayer and Marshall, 1992). See Vickery et. al (2000a) for gusts in hurricanes. Hurricane wind gusts are currently a major issue in defining wind loads. Excellent discussion of the standardization of wind speeds is found in Powell et. al (1994). The terms ‘3 sec gust’, ‘one- minute sustained wind’, and ‘mean hourly wind’ are in common use. Definitions of these terms may be found elsewhere in the textbook. Mobile meteorological towers at Texas Tech and Clemson Universities are designed to obtain additional data on hurricane winds at landfall. The Building Envelope INSTRUCTOR NOTES

FAILURE OF BUILDING ENVELOPE interior pressure interior damage contents damage occupant exposure loss of use relocation expense residences unlivable community disruption It is important to emphasize the consequences of failure of building envelope: Internal pressure doubles forces acting to lift roof and push walls outward. Damage to building interior can exceed cost of building exterior. Damage to building contents may exceed damage to building (Sparks et. al, 1994). Occupants subjected to wind, rain and possible building failure Loss of business Business relocation expense Residences unlivable Disruption of communities The Building Envelope INSTRUCTOR NOTES

HURRICANE EFFECTS Damage to the building envelope (components and cladding) Twelve slides following this title slide illustrate damage to the building envelope caused by hurricanes. The last slide shows both building envelope and frame failures. Breaching of the building envelope can produce major damage to the structure and its contents. Insurance records indicate that total destruction to a residence can result from damage to the building envelope only. Insurance damage algorithm: 30 percent sheathing loss totals contents. If there is damage to the structural frame, destruction is often total, especially in residential construction. The Building Envelope INSTRUCTOR NOTES

ANDREW (1992) The Building Envelope Andrew (1992) American Bankers Life Building in Cutler Ridge, Florida Extensive window glass breakage occurred as winds attacked building from N to SE for 2-3 hours. Insured loss was magnified because of failure of building envelope. The Building Envelope INSTRUCTOR NOTES

CELIA (1970) and ALLEN (1980) The Building Envelope Guaranty Bank Building, Corpus Christi, Texas Roof gravel impacts broke windows in both hurricanes. First published record of debris impact on glass by Minor, Mehta, and McDonald (1972) Insurance concerns focused on residential construction. Texas Catastrophe Property Insurance Association (TCPIA) was formed following Celia (now Texas Windstorm Insurance Association, TWIA). The Building Envelope INSTRUCTOR NOTES

CELIA (1970) and ALLEN (1980) The Building Envelope Guaranty Bank Building, Corpus Christi, Texas Evidence that roof gravel impacts broke windows Glass was annealed The Building Envelope INSTRUCTOR NOTES

ALLEN (1980) The Building Envelope Allen (1980) Spohn Hospital, Corpus Christi Tempered insulating glass unit (failure in outer lite only) Gravel from adjacent roof impacted glass. Hurricane related winds were only about 70 mph in Corpus Christi. The Building Envelope INSTRUCTOR NOTES

FREDERIC (1979) The Building Envelope Frederic (1979) Singing River Hospital, Pascagoula, Mississippi Gravel from roofs in foreground broke windows. One-half of rooms taken out of service. The Building Envelope INSTRUCTOR NOTES

FREDERIC (1979) The Building Envelope Frederic (1979) Singing River Hospital, Pascagoula, Mississippi. Gravel impacts may be observed on vision lites. Vision lites were annealed glass. The Building Envelope INSTRUCTOR NOTES

FREDERIC (1979) The Building Envelope Frederic (1979) Motel damaged by internal pressure following failure of windward wall. Windborne debris broke windward wall windows. Roofing panels were removed; steel joists remained in place. Principal structural frame is intact; contents and functionality destroyed The Building Envelope INSTRUCTOR NOTES

ANDREW (1992) The Building Envelope External insulation and finish system (EIFS) Some cladding systems are more susceptible to wind damage than others. EIFS shown here is particularly vulnerable. Note most glass panels on first floor survived, EIFS failed. The Building Envelope INSTRUCTOR NOTES

ALICIA (1983) The Building Envelope Alicia (1983) Aerial view of downtown Houston, Texas Hurricane force winds approached from the Northeast and slowly changed direction to approach from the Southeast as the hurricane passed west of downtown. Gravel from one roof broke windows in 90 degree arc (Beason, et. al, 1984). Glass breakage is summarized in Minor (1984). The Building Envelope INSTRUCTOR NOTES

ALICIA (1983) The Building Envelope Alicia (1983) 1100 Milam (foreground) and Entex Buildings from street level. Entex building glass: spandrel is tempered (broke and fell from opening); vision is annealed (sustained ‘dings’ but did no shatter). The Building Envelope INSTRUCTOR NOTES

ANDREW (1992) The Building Envelope Andrew (1992) NCNB Building in Kendall, Florida Note window glass failures limited to windward wall (north face). Tempered glass windows were able to contain internal pressure. Damage to interior was confined to offices adjacent to windows and hallway. The Building Envelope INSTRUCTOR NOTES

RESIDENTIAL CONSTRUCTION Damage to roof covering, roof deck, windows, and doors Damage can approach “total destruction” even though principal structural frame is preserved. Rain entering building is especially destructive. The Building Envelope INSTRUCTOR NOTES

HOUSING The Building Envelope Failure of principal structural frame in residential construction Beachfront residences damaged by Hurricane Frederic. Failures of roofing systems were due to overall uplift pressures. House in center was shuttered but entire roof is gone. Nearest house experienced windward wall failure Weak link in vertical load path is rafter/truss-to-wall connections. The Building Envelope INSTRUCTOR NOTES

SUMMARY the hurricane is a special type of windstorm sustained, turbulent winds, change slowly in direction and carry debris integrity of the building envelope is critical there are severe consequences when envelope is breached Summary of hurricane winds, probabilities and effects The hurricane environment(wind, debris, surge, rain) is especially harsh. Loss of the building envelope invites total loss of building interior and contents. Designing for full internal pressure may save structure, but interior, contents, use of building, and business are lost. Residential construction is particularly vulnerable to damage through loss of windows, doors, and roof covering. The Building Envelope INSTRUCTOR NOTES