Multi-Hazard Mitigation Plan: 05. Tropical Cyclones

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Chapter•5:Hazard Analysis—Tropical Cyclones The test standards also include testing of the panel system for 9000 cycles of pressure fluctuations, of various magnitudes up to the design pressure, after the panel has been subjected to the missile impacts. The tests performed at Clemson University primarily focused on the missile impact portion of the test procedure. Additional tests were conducted where the panels were subjected to uniform wind pressures using air bags or a vacuum chamber. The bulk of these tests were performed to determine the pressure at which the panel would break or be sucked off the wall system. In these tests, the pressures were monotonically increased until failure occurred in the fastening system or to one of the bracing members. Two additional tests were performed using the 6-foot by 6-foot 8-inch sliding glass door protection system to determine the deflection as pressure was increased that pushed the panel against the opening. Two panels were tested for each thickness of plywood and for three sizes of openings (2-foot by 4-foot, 3-foot by 5-foot, and 6-foot by 6-foot 8-inches). Generally, the missile impacts caused localized punching shear failures and it was possible to impact a single panel with multiple missiles. The overall observation is that the shutter systems are adequate to provide protection from the 8-pound 2x4 missile traveling at 27 mph since the threshold for penetration is slightly higher than 24 mph with the 9-pound 2x4 missile. At 24 mph, localized damage to the cross members and indentation of the panel was the rule. There were a couple of instances where a 9-pound missile penetrated at 24 mph, however these were relatively rare. There was a marginal increase in resistance for the 5/8-inch thick sheathing as opposed to the 1/2-inch sheathing. The increase was generally on the order of 1 to 2 mph in missile speed for penetration. The 5/8-inch sheathing did seem to perform better than the 1/2-inch sheathing when subjected to the missile impacts at 45 degrees. The missile bounced off the 5/8-inch sheathing more often than for the 1/2-inch sheathing. In general, 9-pound missiles penetrated the panels at speeds between 25 and 28 mph. The performance of the panels subjected to oblique angle impacts seemed to depend to some extent on whether the missile impacted with the long edge (3-1/2 inch)oriented vertically or horizontally. Local damage to the lx') lumber used at the laps between the plywood sheets was common if impact occurred on the 1x3 and fasteners withdrew or the 1x3 split when the impact occurred near the W. The screws connecting the lx3s to the panels were fairly short and provided only minimal penetration into the plywood sheathing. In summary, the 1/2-inch and 5/8-inch shutters both clearly provide substantial protection from missile impacts associated with a 4.5-pound 2x4 missile and essentially are very close to completely rejecting impacts of an 8-pound 2x4 traveling at 40 feet per second (27 mph). Based on these test results, we conclude that the HHRF protective panels should be an adequate level of protection against windborne debris provided that they are properly constructed and installed. Pressure cycling tests should be conducted to ensure that the anchor design meets the full ASTM standard. Each test specimen is required to receive two such impacts followed by cyclic pressure loading similar to that experience under hurricane conditions. The glazing was required to resist the pressure loading with no crack forming longer than five inches through which air could pass or with no opening forming which a three-inch diameter sphere could pass. 5-18 Hawaii County Multi-Hazard Mitigation Plan