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Fujita Tornado Intensity Scale: A Critique Based on Observations of the Jarrell Tornado of May 27, 1997.


pdf icon Fujita Tornado Intensity Scale: A Critique Based on Observations of the Jarrell Tornado of May 27, 1997. (3019 K)
Phan, L. T.; Simiu, E.

NIST TN 1426; 23 p. July 1998.

Available from:

National Technical Information Service (NTIS), Technology Administration, U.S. Department of Commerce, Springfield, VA 22161.
Telephone: 1-800-553-6847 or 703-605-6000;
Fax: 703-605-6900.
Website: http://www.ntis.gov
Order number: PB98-175136

Keywords:

tornadoes; building technology; Fujita intensity scale; meteorology; structural engineering; wind engineering; wind speeds

Abstract:

On May 27, 1997, several tornadoes hit the Central Texas area in the counties of McLennan, Bell, Williamson, and Travis. The most destructive of these tornadoes swept through a housing area on the outskirts of Jarrell, Texas. Jarrell is a Central Texas town with a population of 410 located approximately 60 km north of Austin, Texas. The Jarrell tornado destroyed about 40 single-family residences and other structures, killing 27 people. A post-storm damage survey was made at Jarrell by a team coordinated by the Office of the Federal Coordinator for Meteorological Services and Supporting Research (OFCM). We report damage observations and conclude on their basis that the worst damage can be explained by wind speeds corresponding to an F3 rating on the Fujita tornado intensity scale (wind speeds of 71 m/s to 92 m/s). An F4 (93 m/s to 116 m/s) rating, or the F5 (117 m/s to 142 m/s) rating officially issed by the National Weather Service (NWS), need not be assumed to explain that damage. We ascribe the NWS rating to the failure of the Fujita tornado intensity scale to account explicitly for the dependence of wind speeds causing specified types of damage or destruction upon the following two structural engineering factors: (1) quality of construction, defined as degree of conformity to applicable standards requirements, and (2) the basic design wind speed at the geographical location of interest.