Multi-Hazard Mitigation Plan: 05. Tropical Cyclones

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Chapter 5:Hazard Analysis—Tropical Cyclones 5.5.1.3 Wind Speed-Up and Structure Type Vulnerabilities Structures are designed to withstand specified wind forces in accordance with the prevailing building code. Wind design pressures have changed over the years in the Uniform Building Code (UBC), increasing from 15 psf(1958-79) to 26.5 psf(1982-88) to 30 psf(1991-97).20 Hawaii County did not adopt the 1982 UBC until 1985, thus any structures built prior to 1985 are designed to an inadequate wind pressure. Subsequent to Iniki (1992), Hawaii County required hurricane ties for single-family construction with the adoption of the 1991 UBC in 1993. To identify vulnerable single-family housing stock, the suggested benchmark year would be thus 1993. The local Hawaii County building code is based on the 1991 UBC and does not take into account topographically induced local wind acceleration which could produce significant directional sensitivity at a given site. The wind speed-up effects arc now reflected in the Hawaii State Building Code, which needs to be adopted by the County of Hawaii per Hawaii Revised Statute Chapter 107,Part II. 5.5.1.4 Critical Facilities Study An all-hazard screening of critical facility buildings in the County of Hawaii has been conducted and a HAZUS MH risk assessment model created to evaluate the expected losses for each building. Two facilities that rank high based on these analyses were evaluated in more detail such that recommended mitigation procedures were developed. A Benefit-Cost Analysis of the mitigation project construction funding was performed. This detailed evaluation will provide the information necessary to submit a PDM grant application for feasible retrofit project. 5.5.1.5 State Building Adoption/Requirements for Hurricane Resistance The 2006 International Building Code will soon be adopted by all Counties in the State of Hawaii through the recently developed State Building code, which each county must adopt by new state legislation after a grace period that is intended to allow development of any specific requirements a particular county may desire. The state building code is intended to ensure regular updates of the building codes and uniformity between the counties. One significant aspect of the adoption of the upcoming adoption of 2006 IBC statewide is the consideration of windborne debris protection for any glazing lower than 60 feet above the ground level in buildings located in a windborne debris region. Hawaii is considered a windborne debris region and consequently the IBC requires impact protection of the glazing. In lieu of glazing protection, the 2003 iBC allows any unprotected glazing in to be considered as openings and consequently the building must be designed for internal pressurization. This provision is omitted from the 2006 IBC for buildings in wind debris 20 "The 1982 to 1997 UBC values were predicated on an 80 mph basic fastest-mile windspeed, approximately equivalent to a 95 mph 3-second peak gust. The 3-second peak gust is the wind parameter now used in American Society of Civil Engineers 7 (ASCE-7),Minimum Design Loads for Buildings and Other Struc- tures, which forms the basis for the International Building Code (IBC). The 3-second gust windspeed standard now established in the IBC is 105 mph statewide, which is slightly greater than the UBC- equivalent 95 mph 3-second gust. Hurricane Hazard Advisory from the Hawaii Multihazard Science Advisory Committee to the State Hazard Mitigation Forum,draft December 2002. 5-16 Hawaii County Multi-Hazard Mitigation Plan