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Coast in the Eye of the Storm, Hurricane Katrina: August 29, 2005 Technical Report No. CMRC 06-1, March 2006 (Final Review) There are a variety of extreme loads imposed on structures by a hurricane. In initial stages of the hurricane, wind and wave action raise the water surface substantially, resulting in a storm surge. As a result, walls of shoreline structures are subjected to a lateral hydrostatic as well as buoyancy loads. Wind driven waves associated with the raised water level during the storm surge impact structures and cause significant structural damage. This wave action is perhaps the most severe structural load during the storm, and is believed to be the cause of most of the damage shown in the figures contained in this report. The high winds accompanying the hurricane primarily damage roofs and exterior structural components, but pose much less of a threat to structures than the storm surge and wave action, which are severe enough in many cases to destroy entire structural systems. Additional associated loads include impact from water-borne and air-borne debris. Foundation erosion may also pose significant risks to structural stability. (p. 4-1) Many (most, if not all in some areas) wood houses along the coastline were completely destroyed. Residences further back from the coastline sustained less serious, if little apparent structural damage. It appears the first row of structures and trees along the coastline absorbed much of the storm surge energy. (p. 4-1) Although Katrina caused significant economic damage from high winds, the extent of wind damage to a typical coastal structure was much less severe than that caused by storm surge. For wind, damage was usually localized to roofing panels, while for storm surge, entire structures were destroyed. Thus, minor revision of current roof standards and then rigorous enforcement would be beneficial. However, there is need to examine land use planning and design for storm surge loading. (p. 5-1) Most light-frame wood structures subjected to storm surge were destroyed and it appears failure initiated at fasteners. However, it is not known whether strengthened connections alone would decrease damage because the overall structural capacity of such structures when lateral storm surge load is considered is much less than that of typical engineered structures that survived. (p. 7-2) |
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