On the evening of May 3, 1999, an outbreak of tornadoes tore through parts of Oklahoma and Kansas, in areas that are considered part of "Tornado Alley", leveling entire neighborhoods and killing 49 people. The storms that spawned the tornadoes moved slowly, contributing to the development and redevelopment of individual tornadoes over an extended period of time.
On May 10, the Federal Emergency Management Agency’s (FEMA’s) Mitigation Directorate deployed a Building Performance Assessment Team (BPAT) to Oklahoma and Kansas to assess damage caused by the tornadoes. The team was composed of national experts including FEMA Headquarters and Regional Office engineers and staff; a meteorologist; architects; planners; wind engineers; structural engineers; and forensic engineers. The mission of the BPAT was to assess the performance of buildings affected by the tornadoes, investigate losses, and describe the lessons learned. This report presents the BPAT’s observations, conclusions, and recommendations, which are intended to help communities, businesses, and individuals reduce future injuries and the loss of life and property resulting from tornadoes and other high-wind events.
The observations, conclusions, and recommendations in this course are grouped to address issues concerning (1) residential property protection, (2) non-residential property protection, and (3) personal protection and sheltering. The BPAT’s findings are correlated with the Fujita damage scale, which ranks tornadoes according to the damage they cause, and general tornado intensity (Table 1-1).
During the field investigation, the BPAT investigated buildings to identify successes and failures that occurred during the tornadoes. Building failures were identified as being directly struck by the vortex or core of the tornado, affected by winds outside the vortex of the tornado, or out on the extreme edge or periphery of the tornado path. Considerable damage to all types of structures throughout Oklahoma and Kansas was observed. Failures occurred when extreme winds produced forces on the buildings that they were not designed to withstand. Failures also occurred when wind-borne debris penetrated the building envelope, allowing wind inside the building that again produced forces on the buildings that they were not designed to withstand. Additional failures observed were attributed to improper construction techniques and poor selection of construction materials. It was a goal of the BPAT to determine if any of the damage observed to both residential and non-residential buildings was preventable.
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