Volume 35, Number 10, October 2000
several factors must be considered when performing these installations
by Robert Foster
As the heat, common in southern states, combines with colliding pressure systems, violent thunderstorms and hurricanes loom on the horizon. Not surprisingly, demand for impact-resistant products is increasing beyond South Floridas borders as other coastal and off-shore environments create strict codes, consider evacuation plans and weigh property risks. Building owners also are sleeping easier knowing the additional advantages of high-performance and protective products that provide increased security and improved acoustic performance.
Since Hurricane Andrew devastated South Florida in 1992, the glass and construction industries have focused on improving products that withstand the violent intrusion and devastation wrought by hurricanes and storms to provide protection for life and property. The initial cause of damage is windborne debris, sometimes as large as roofs, tree limbs and doors, lifted and hurled by high winds until they smash and force their way inside buildings. When this happens, the sudden increase of the buildings internal air pressure typically exceeds exterior building design capabilities.
Large and Small Missile Tests
Windborne debris testing of impact-resistant products requires stringent simulations and usually is carried out by qualified independent laboratories. Large and small missile tests, followed by severe pressure cycling tests, are carried out in accordance with Dade County Protocols PA 201, 203, the Southern Building Code Congress International Standard, SSTD-12 and ASTM E 1886.
For products installed up to 30 feet above ground, the large missile test creates dramatic simulations of hurricane mayhem. Two- by 4-inch timbers shoot from a cannon, simulating uprooted trees or windborne debris hurtling towards glass doors, windows and curtainwall at hurricane speeds. The laminated glass infills are designed to crack but not fall from the opening or allow penetration. Despite repeated test bombardments at different locations on the product, the timber must not penetrate. The same impact tested product is then subjected to severe pressure testsa series of 4,500 inward and 4,500 outward pressure cycles simulating hurricane wind forces. No significant opening through which air can pass may occur.
For products installed more than 30 feet above ground, the small missile test simulates smaller debris that causes damage as it is lifted to higher altitudes, such as windborne roof gravel. Quantities of two-gram steel ball bearings are repeatedly fired from an air cannon at high speed. Again, no significant opening may occur, after which the same series of pressure cycles are repeated.
High-performance laminated glass used in doors, framing, windows and curtainwall is critical to protect property in potential storm and hurricane ravaged locations. Laminated glass products generally are used to meet the requirements of the large missile test, while the traditional PVB interlayer is suitable for most small missile applications. Many impact-resistant installations are structural silicone glazed (SSG) to ensure a strong seal and durable structural attachment to the framing.
Consider the Design Load
When considering an impact-resistant installation, design load is critical. For greatest protection, check the small print of test result information to ensure that your requirements are amply covered. For example, our HPS® sliding doors are available in four different performance ranges for low- and medium-rise applications. For high-rise coastal applications requiring greater design load and superior water performance, HPX Sliding Doors are large missile impact-tested for severe weather conditions. Water penetration and drainage are vital considerations in locations where extreme weather conditions with driving rain and high winds are typical. Careful checking of test results is not only prudent, but critical.
Access to engineering experience and expertise for questions regarding the complications of severe weather installations are an added bonus for glazing contractors, no matter what the project. In addition, working with a supplier that provides single-source responsibility and a wide range of products can simplify the complex requirements of some impact-resistant installations.
As building codes in more areas are amended to compensate for severe storm devastation and water damage, glazing contractors can anticipate an increased demand for impact-resistant, high-performance products. Glass manufacturers are providing increasingly protective products that can survive rigorous testing and also are designing products that minimize the destruction caused by severe weather.
Installations are becoming more complex in these locations, but the added advantages and peace of mind a proper installation creates for owners and occupants is worthwhile.
Robert Foster serves as senior marketing manager for Kawneer Company, based in Norcross, Ga.
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