Multi-Hazard Mitigation Plan: 05. Tropical Cyclones

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Chapter•5:Hazard Analysis—Tropical Cyclones regions. However, risk analyses found that the benefits of providing windborne debris protection for all glazing did not exceed the costs for the relatively low hurricane hazard in Hawaii. Therefore, the state building code amendments to the 2006 IBC provide designers with flexibility in allowing Occupancy Category II buildings and some Occupancy Category ITT buildings (not healthcare or high occupancy facilities) to be designed with unprotected glazing provided they are designed for the internal pressurization. If a residential building is not provided with glazing protection then it must have a residential safe room installed which does have appropriate glazing protection and must satisfy other structural and non-structural criteria. Public hurricane shelters must also satisfy these criteria. Where used, debris protection for glazing may be in the form of a transparent protective film, on the exterior surface or between glazing layers in laminated glass. Alternatively, window shutters, precut removable plywood panels or another system may be used. Any protective film or other system must undergo testing based on ASTM E 1996 to verify the required level of protection. The University of Hawaii has recently started operation of a wind cannon capable of testing strengthened windows and other debris protective devices to the ASTM standard. This is intending to increase the local availability of products and ultimately reduce the cost of providing windbome debris protection to the glazed areas of a structure. Plywood Shutter Tests Because the HHRF plywood shutter design had not been tested against any of the three windborne debris standards discussed in Section 6.1.1, Applied Research Associates contracted with Dr. Timothy Reinhold of the Wind Load Test Facility at Clemson University to perform exploratory missile impact and pressure resistance tests on six HHRF storm panels. Although it was not feasible to conduct the cyclic loading tests specified in the ASTM standard, the tests did provide valuable information in the impact resistance and ultimate pressure resistance of the HHRF panels. The largest missile specified by ASTM, SBCCI, and the SFBC standards is a 9-pound 2x4 piece of lumber. The missile is projected at the test object using an air canon and strikes the test object end on, perpendicular to the surface. For residential buildings, the missile impact speed specified for regions with the highest design wind speeds in the US is 50 feet per second (34 mph) in all three standards. In order for a product to pass the test, the SFBC impact standard allows no penetration of the protective system while the SBCCI and ASTM standards do allow penetration, provided the hole is small enough to prevent a 3 inch sphere from passing through the hole. The SBCCI and ASTM standards include smaller (lighter) missiles in regions with lower design wind speeds. For gust speeds between 110 and 130 mph, the ASTM standard requires that shutters resist a 4.5-pound 2x4 at 40 feet per second (27 mph). Since Hawaii has a basic design wind speed of 105 mph (gust) in ASCE 7-98, the design speed falls just below the light missile standard. Consequently, impact protection systems for Hawaii would need at most according to current standards)to resist the impact of a 4.5-pound 2x4 traveling at 40 feet pet- second (27 mph). This impact momentum corresponds to that of a 9-pound 2x4 traveling at 20 feet per second(12 mph). All tests were conducted using a 9-pound 2x4. In addition to the straight-on missile impact tests, tests were also conducted with missiles impacting at an oblique angle of 45 degrees. 5-17 Hawaii County Multi-Hazard Mitigation Plan