Presentation on theme: "Tropical Storms and Hurricanes Updated 2008. Tropical Storms and Hurricanes Introduction Tropical storms and Hurricanes are formed from tropical disturbances."— Presentation transcript:
Tropical Storms and Hurricanes Updated 2008
Tropical Storms and Hurricanes Introduction Tropical storms and Hurricanes are formed from tropical disturbances that travel across the Atlantic ocean toward the U.S. coast line. In 2004, Hurricanes and tropical storms were responsible for an estimated $50 billion dollars in damage. Five Hurricanes made landfall in the state of Florida. Three of them had at least 115 mph sustained winds. In 2005, the Atlantic Hurricane season was the most active season in recorded history. The impact of the season was widespread and ruinous with at least 2,280 deaths and record damages of over $128 billion USD.
Tropical Storms and Hurricanes How Hurricanes Form Tropical Disturbance: An area of organized convection, originating in the tropics that maintains its identify for 24 hours or more. It is often the first developmental stage of any tropical depression, tropical storm or hurricane. Tropical Storm: A severe storm that develops offshore over tropical seas. When wind speeds reach 39 mph, the tropical disturbance becomes a tropical storm and is given an official name. Hurricane: When a tropical storm takes a cyclonic form and has reached a constant wind speed of 74 mph or more. The eye of the storm is usually 20 – 30 miles wide and can extend over 400 miles. Strong hurricane windows can inflict moderate to severe damage to buildings and may cause flooding in coastal areas.
Tropical Storms and Hurricanes Saffir – Simpson Scale The Saffir – Simpson Hurricane scale is a Category 1 to Category 5 rating based on the hurricane’s present intensity. The scale is used to give an estimate of potential property damage and flooding expected along the coast. Wind speed is the determining factor in the scale, as storm surge values are highly dependent on the shape of the coastline.
Tropical Storms and Hurricanes Property Damage Flying debris is a major concern, but research has shown that most destructive damage occurs when the building envelope is breached. A breach of only 10% of the building envelope, due to a broken window, can destroy a structure. The increased wind pressure on the anchoring of the roof to the walls and the walls to the floor is typically what leads to building failure.
Tropical Storms and Hurricanes Property Damage Continued.. Theory Of Destruction Debris penetrates the building envelope. Negative pressure builds up from the inside Roof lifts off allowing water to enter When a window is shattered or blown out, the building becomes partially enclosed and as a result, wind pressure on the roof and walls is significantly increased.
Tropical Storms and Hurricanes Storm Activity in was the most active hurricane storm season in recorded history. The impact was widespread and ruinous with over 2,000 deaths and record damages of over $128 billion dollars. A record twenty-eight tropical and sub- tropical storms formed, of which fifteen became hurricanes. Five became Category 4 hurricanes and four reached Category 5 strength.
Tropical Storms and Hurricanes Storm Activity in 2006 & was a fairly inactive storm season. It was unusual that no hurricanes made U.S. landfall marked an earlier beginning to a fairly active season when Subtropical Storm Andrea formed on May 9, 2007 and Tropical Storm Olga developed on December 11 th was fairly active with 15 named storms, though their intensities did not meet predictions.
Building Codes and Wind Loads Introduction When Hurricane Andrew hit Florida in August of 1992, causing an estimated $25 billion dollars in damages, it became the “wake up call” for the construction industry. Andrew revealed wind zones were understated, existing standards were not being adhered to and codes were not being enforced. As a result, demands for missile impact tests, standards and building codes have been put in place and are subject to stringent enforcement.
Building Codes and Wind Loads Impact of Hurricane Andrew As a result of Hurricane Andrew, codes and standards were revised to require: Higher Wind Loading: Coastal wind load charts were redefined significantly higher. Effective March 8, 2007, Panhandle is no longer exempt from the wind-borne debris region. Negative Pressures: Building components required to withstand high wind loads, greatest impact realized from negative pressure loads. Impact and Cyclic Testing: Cladding and building components must be tested and certified for compliance.
Building Codes and Wind Loads Code Expansion Codes originally developed for Florida have expanded from Texas, along the Gulf and up through the Atlantic seaboard to Maine. This map shows wind speeds for areas along the southeastern coast and where codes are in place. The contour lines on this map are wind speed lines, not design pressures. Wind speeds are converted to design pressures using ASCE-7 (American Society of Civil Engineers). Source: Institute of Business and Home Safety
Building Codes and Wind Loads Current Building Codes Most building codes used in the United States are based on the International Building Code (IBC), which references the American Societywww.iccsafe.org of Civil Engineers (ASCE), standard ASCE-7 “Minimum Design Loads for Buildings and Other Structures” for wind load design. Even those jurisdictions that have their own statewide building code, such as Florida, Texas, and North Carolina, typically reference the same wind load provisions as those found in the IBC (with some local amendments). For instance, in Florida, Miami Dade and Broward counties require buildings to utilize tested and approved windborne debris protection systems, such as shutters or impact windows.
Building Codes and Wind Loads ASCE 7 Development ASCE - 7 outlines basic wind load provisions and procedures to convert basic wind speed into design pressures based on several variables. The wind load provisions of ASCE - 7 have developed over the years. The most current versions is ASCE 7 – 05. Section 6 of ASCE – 7 deals with wind load calculations for “Main Wind-Force Resisting Systems” and “Components and Cladding” Standard Development ASCE 7 – MPH Maximum ASCE 7 – 93ANSI 58.1 Integration ASCE 7 – MPH Maximum ASCE 7 – MPH Maximum ASCE 7 – 02Current Standard incorporated IBC provisions
Building Codes and Wind Loads Terminology Design Load: Also referred to as design pressure (DP), design load is in the air pressure that a window system must be able to withstand as determined by the project architect in accordance with applicable codes. Design loads are usually expressed in both positive and negative pounds per square foot (PSF). Wind Load: Also referred to as wind pressure, wind load is the amount of pressure exerted by the wind on a window system. Wind loads are generally expressed in pounds per square foot (PSF) and are not to be confused with basic wind speed, which is usually expressed in miles per hour (MPH).
Building Codes and Wind Loads Terminology Cont’d… End Zone: The end zone consist of the area within 10% of the shortest building dimension to the edge of the structure. End zones are essentially the corners of a structure and typically require higher design pressures. Interior Zone: The interior zone consists of the area between the end zones. Interior zones typically require lower design pressures than end zones. Opening Area: Opening area refers to the size of the window opening and is used to determine design pressures as per ASCE – 05. Large openings typically have lower design pressures than smaller openings. Weighted Area: When an opening falls partially within an end zone, the total window area is averaged based on the square footage located in each zone.
Building Codes and Wind Loads Which code applies? Georgia State TexasAlabama North Carolina South Carolina Florida County ? SBCCI IBC NCBCIBC County Texas Department Of Insurance for Coastal Counties No Hurricane Code for Other Counties Florida Building Code (FBC) for Other Counties Local Building Code for Dade And Broward
Building Codes and Wind Loads Who Approves Impact Products? There are three major product approval Agencies for impact resistant glazing: Texas Department of Insurance Florida Building Commission Miami – Dade Product Approval These web sites provide information on Approved impact glazing products.
Building Codes and Wind Loads Who Conducts Inspections? For standard applications, inspections are conducted by the local building department, as legislated by the County Code Compliance Office. Special Inspectors or Consulting Engineers may be brought in to inspect non-standard applications. FEMA projects are typically inspected by Special Inspectors, while schools are typically subject to inspection by local and state building inspectors.
Building Codes and Wind Loads What’s Really Required? Design Pressure Ratings: Elevation drawings should indicate design pressure ratings for the structure, including end zone and interior zone pressures as determined by the engineer of record in accordance with ASCE - 7. Building Exposure: Listing of Building Exposure as defined by ASCE - 7. Structures in urban, suburban, or wooded areas are typically Exposure B, while structure in open fields or on coast lines are typically Exposure C. Basic Wind Speed: Basic Wind Speed for the site represented in MPH. This is based on the 50-year average of the peak wind speed at a given height and exposure (typically 33’ for Exposure C) averaged over three seconds.
Building Codes and Wind Loads What’s really Required? Importance Factor: A safety factor related to the degree of hazard to human life and property. Various “essential use” facilities, such as hospitals, have an importance factor of 1.15, as compared to residential construction (1.00). Site Specific Shop Drawings: All submissions should include supporting site specific shop drawings for all fenestration products, fenestration components and exterior cladding. Notices of Acceptance: Submissions should also include individual product Notices of Acceptance (NOA’s) or product approvals as issued by the governing code compliance office from each participating trade.
Building Codes and Wind Loads Summary The codes and standards implemented in Response to Hurricane Andrew resulted in: Higher wind load provisions and higher structural loading Large and small missile impact testing and cyclic testing Improved code reinforcement at the local, regional and state levels Today’s standards help provide increased Protection for hurricane-prone areas.
Wind Load Testing not to code Buildings to code
Wind Load Testing Introduction The IBC requires fenestration in coastal areas to be AAMA certified, which requires windows to undergo structural, impact and cyclic testing. Small and large missile impact testing helps stimulate the ability of a window to resist hurricane driven debris. Cyclic testing is performed after impact testing and is designed to simulate positive and negative pressures of hurricane-force winds. Building heights > 30’ – Small Missing Testing
Window Load Testing Test Standards The standard test method for cyclic testing referenced by the IBC and AAMA, is ASTM E “Standard Test Method for Performance of Exterior Windows, Curtain Walls, Doors and Impact Protective Systems Impacted by Missile (s) and Exposed to Cyclic Pressure Differentials”. Small and large missile impact testing is covered by ASTM E “Standard Specification for Performance of Exterior Windows, Curtain Walls, Doors and Impact Protective Systems Impacted by Windborne Debris in Hurricanes” Equivalent Miami-Dade and Broward standards are TAS “Impact Test Procedure”, TAS “Criteria for Testing Impact and Non Impact Resistant Building Envelope Components Using Uniform Static Air Pressure”, and TAS “Criteria for Testing Products Subject to Cyclic Wind Pressure Loading”.
Wind Load Testing Large Missile Impact testing is performed on windows to simulate the ability of the frame and glazing material to resist hurricane-driven debris. Large missile testing is an 8’ long, 9lb, 2x4 board shot twice at a window at a speed of 50’ feet per second. Window products that are large missile tested are typically used on elevations from ground up to 30’ or close to a debris generation point.
Wind Load Testing Small Missile Small missile testing involves 2 gram steel balls (to represent roof rock) shot at the window twice product at a speed of 130’ per second. Windows that are small missile tested are typically used on elevations at heights over 30’. Window products that are large missile tested can also be used at heights over 30’, however they are typically more expensive. Building heights > 30’
Wind Load Testing Cyclic Testing Following missile testing, products are subjected to cyclic testing designed to simulate the positive and negative pressures of hurricane-force winds. Windows are subjected to 9,000 cycles of positive (inward-acting) and negative (outward-acting) pressures. These positive and negative pressures are related to the design pressure and are applied in a prescribed sequence in cycles lasting 1 to 3 seconds.
Wind Load Testing Cyclic Testing Cont’d….. For example, given a design pressure of 100 psf, the sample would first be subjected to positive pressures from 20 psf to 50 psf for 3,500 cycles. Most failures occur when the sample is subjected to positive pressures from 0.4 DP to 1.0 DP for 100 cycles. Test samples are deemed to have passed cyclic testing if no openings larger than 3” in diameter, or tears or cracks longer than 5” appear. Sequence Pressure Cycles Positive 0.2 DP – 0.5 DP 3,500 Positive 0.0 DP – 0.6 DP 300 Positive 0.5 DP – 0.8 DP 400 Positive 0.3 DP – 1.0 DP 100 Negative 0.3 DP – 1.0 DP 50 Negative 0.5 DP – 0.8 DP 1,050 Negative 0.0 DP – 0.6 DP 50 Negative 0.2 DP – 0.5 DP 3,350 Sequence Pressure Cycles Positive 0.2 DP – 0.5 DP 3,500 Positive 0.0 DP – 0.6 DP 300 Positive 0.5 DP – 0.8 DP 400 Positive 0.3 DP – 1.0 DP 100 Negative 0.3 DP – 1.0 DP 50 Negative 0.5 DP – 0.8 DP 1,050 Negative 0.0 DP – 0.6 DP 50 Negative 0.2 DP – 0.5 DP 3,350
Building Outside the Box Introduction In some situations, the standard procedures for specifying windows that meet current building code requirements may not apply. For instance, what if a particular window product has not been tested in the size required for the project? What if the product does not have a NOA? What if the wind loads are unusually high? What about mid-rise and high – raise challenges?
Building Outside the Box Project Specific Testing For projects that require unique configurations of glazing that have not been tested, it is possible to conduct project specific testing. In these instances, large mock ups must be constructed in order to undergo impact and cycle testing. Project specific testing can be costly and time consuming. As a result, it is important to plan design criteria early and involve manufacturers.
Building Outside the Box Wind Tunnel Testing In addition to project specific testing, wind tunnel testing is an acceptable alternative to straight line, deductive calculations. For structures with high design pressures, wind tunnel testing can reduce design pressures by 30% Reduced loading can significantly lighten the structural performance requirements of the window and save thousands in material costs.
Building Outside the Box Comparative Analysis vs. Rational Analysis Engineering analysis can be used to quality unique window openings, however it is Important to distinguish between comparative analysis and rational analysis: Comparative Analysis: Comparative analysis uses actual test criteria as a basis for the evaluation of a product. There are allowable spans that can be used as a known value when sizing varies. Comparative analysis is commonly used when project requirements exceed current test sizes. Rational Analysis: Rational analysis is not based on test criteria and essentially consists of an engineer’s opinion regarding a particular product. Although it can be based on logical or calculated deductions, it is not recognized by most certifying entities as an acceptable method for analyzing impact products.
Building Outside the Box Points to Remember If you plan to test, keep in mind that the largest known job size component should be tested along with any accessories that will be used with the system. Multiple or triple arrangements for fenestration products, including mullions, are extremely important. This is often overlooked! It is often thought that rational analysis can be used to compensate for any testing insufficiencies, however this assumption is incorrect. Rational analysis is not permitted for impact products. Testing involves significant material costs, engineering costs, laboratory costs, and certification fees. Moreover, lead times for testing and certification often collide with critical paths. Retesting and remedial repairs, if necessary can create unexpected delays. In some cases, product approvals can take up to one year.
Windborne Debris Protection Systems
Windborne Debris Protection System Introduction In Florida, both Miami-Dade and Broward counties require buildings to incorporate tested and approved windborne debris protection systems These debris protection systems may consist of protective shutter systems or impact resistant window systems. Impact resistant glazing is able to resist wind pressures and often provides better protection than shutter systems.
Windborne Debris Protection Systems Protective Shutter Systems Manufacturers offer several different Types of protective shutter systems: Corrugated Panels Plywood Panels Polypropylene Panels Polycarbonate Panels Accordion Panels Ease of installation and operation are Both important factors to consider.
Windborne Debris Protection Systems Protective Shutter Systems Cont’d….. Protective Shutter Systems Cont’d… Protective shutter systems have several Drawbacks compared to impact glazing: Most shutter systems are difficult to install and labor intensive to operate Permanent shutter systems are highly invasive and require maintenance Temporary shutter systems tend to be bulky and can be difficult to store In addition, shutter systems are typically not Practical for multi-story applications
Windborne Debris Protection Systems Impact Resistant Glazing Impact resistant glazing systems are specifically designed to meet strict building codes and the toughest coastal weather challenges. Impact glazing provides 24 hour protection that offers maximum protection with minimum effort. Impact resistant glazing products offer high design pressure ratings and are tested to withstand the most severe hurricane-force wind loads.
Windborne Debris Protection Systems Impact Resistant Glazing Cont’d…… Impact resistant glazing offers several Advantages over protective shutters: Impact glazing is a practical solution for both new or retrofit construction Impact glazing offers 24 hour protection with no action required. Impact glazing is more aesthetically appealing alternative to shutters The use of impact resistant glazing may Also help reduce insurance premiums.
Windborne Debris Protection Systems Wind Speed vs. Wind Pressure When choosing between a shutter system and impact resistant glazing, it is important to distinguish between wind speed and wind pressure. Shutter systems can handle gusts and debris, however they cannot protect a building from wind pressure. Wind pressure easily works it’s way around a shutter system to the glass surface. Impact glazing is the only solution that resists wind pressure.
Impact Resistant Glazing Systems
Impact Resistant Glazing Systems Introduction Impact resistant glazing is created by bonding or laminating several lites of glass together with PVB, urethane or resin innerlayer. Insulated impact glazing has also been developed to provide improved thermal efficiencies. When designing with impact resistant glazing, it is important to consider the configuration of the product in terms of the existing or future debris field. Tempered, Heat Strengthened, or Annealed Typical glass thickness: 1/8” to ¼” PVB Thickness.090”
Impact Resistant Glazing Systems Characteristics Impact resistant glazing products consist of multiple lites of glass that are bonded or laminated together by a 0.06” to 0.10” innerlayer. This innerlayer typically consists of PVB or in some instances, urethane or resin. The number of lites and the thickness of each lite and the innerlayer can be varied in order to achieve the required performance characteristics.
Impact Resistant Glazing Systems Design Flexibility Impact glazing is typically available in a variety of sizes and configurations, including casement, fixed, sliding and double and single hung windows. Impact resistant glazing can also be manufactured using tinted glass in a variety of colors as required. Reflective and low-emissivity (Low-E) coatings can also be applied to the glass surface in order to provide solar and thermal control.
Impact Resistant Glazing Systems Advantages of Laminated Glass In addition to impact resistance, laminated glass also provides several other Advantages: Increased Safety and Security: Laminated glass can be used as safety glazing and offers increased resistance to forced entry. Depending on its thickness, laminated glass can also be used to provide bullet and blast resistance. Reduced Sound Transmission: Laminated glass reduces the amount of sound that is transmitted by the glass surface. This results in higher Sound Transmission Class (STC) ratings and a quieter, more comfortable interior environment. Increased Energy Efficiency: Laminated glass filters out more than 99% of the sun’s harmful ultraviolet rays. This helps reduce fading of interior materials and improves energy efficiency.
Impact Resistant Glazing Systems Insulated Impact Glazing Impact resistant glazing was originally developed for the warmer coastal climate of Florida, there were no requirements for thermal values. As impact requirements changed up along the coast, insulated impact glazing has become a necessity. Insulated impact glazing is similar to standard impact glazing in terms of aesthetics. The difference is the air space between the lites of glazing.
Impact Resistant Glazing Systems Insulated Impact Glazing Cont’d….. Insulated impact glazing offers impact resistance, UV protection and sound attenuation similar to that of standard impact glazing. Insulated impact glazing offers superior thermal performance and significantly lower U-values. The addition of a low-emissivity coating to the second glass surface can dramatically reduce solar heat gain and increase light transmittance.
Impact Resistant Glazing Systems Design Considerations In many cases, it is also important to consider the debris field that might be generated from future surrounding developments. A new structure built next to an existing structure could significantly alter the potential debris field. In this case, small or large missile impact glass should be considered where a potential elevated debris field exists or is expected to exist in the future.
Impact Resistant Glazing Systems Design Considerations Cont’d……. Another design consideration for impact glazing is how to configure the tested products in order to accommodate larger openings. In this case, tested products can be installed side by side, separated by mullions, to create bays of windows. From an engineer’s perspective, one large opening has been divided into a series of smaller openings that meet the necessary requirements.
Impact Resistant Glazing Systems AAMA Certification When specifying impact resistant glazing systems, it is important to look for a manufacturer who is a member of AAMA. AAMA memberships helps to ensure quality performance and consistency in manufacturing. American Architectural Manufacturers Association (AAMA)