Tornado Damage Assessment for Structural Engineers

摘要

The number of tornadoes reported annually in the U.S. has steadily increased over the past 50 years. In recent times, the U.S. has averaged 1,200 tornadoes per year. The central portion of the U.S. has been dubbed “tornado alley” since more tornadoes have formed in this area than the rest of the world. The unique combination of warm gulf air, cold artic air, and western mountain ranges creates conditions that produce frequent supercell thunderstorms – which will on occasion spawn strong tornadoes. Given the relatively large quantity of strong tornadoes in recent years, structural engineers have had many opportunities to investigate building damage caused by these destructive weather phenomena. Prospects for building damage assessment will likely continue to increase in the near future. rnThe purpose of this paper is to provide structural engineers with an understanding of basic damage assessment to buildings from tornado events. We will review how high wind forces and large hail from tornado events may damage a building, and delve into situations where the structural engineer must discern between damage caused by a tornado event and damage caused by other means. We will review several case studies depicting damage (both obvious and not-so-obvious) from recent tornadoes, including a 2004 tornado that killed 8 people in Utica and Joliet, Illinois, and a tornado that struck Caruthersville, Missouri in 2006. We will also review how tornadoes are classified per the Fujita system, and how this system was revised to the Enhanced Fujita scale beginning in February, 2007.rnThe author has been involved with damage assessment to a variety of structures that were subjected to forces from recent tornadoes in the central portion of the U.S. (i.e., Midwest). The author has also performed hundreds of investigations from storm damage, including tornadoes, hurricanes, hail, rain, and snow events over the past several years.