Dual-Objective-Based Tornado Design Philosophy

Tornadoes represent a unique natural hazard because of the very low probability of occurrence, short warning times (on the order of only a fewminutes), and the intense and destructive forces imposed on engineered and nonengineered buildings. The very low-probability/very high-consequence nature of a tornado strike makes designing for survival and reducing damage under typical financial constraints a substantial challenge. On April 27, 2011, an enhanced Fujita (EF) 4 (EF4) tornado devastated an almost 10-km (5.9-mi) long, 0.8-km-wide (1/2-mi-wide) path, through the city of Tuscaloosa, Alabama, and continued on the ground for 130 km (80 mi). This paper presents the design concept that resulted following a week-long data reconnaissance deployment throughout the city of Tuscaloosa by the authors. The dual-objective philosophy proposed herein is intended to focus on both building damage and loss reduction in low-to-moderate tornado wind speeds and building occupant life safety inmore damagingwind-speed events such as EF4 andEF5 tornadoes. The philosophy articulates a designmethodology that is the basis uponwhich structural engineeringwas formed—namely, provide life safety and control damage—but the new philosophy is focused at separate tornado intensity levels. DOI: 10.1061/(ASCE)ST.1943-541X.0000622. © 2013 American Society of Civil Engineers. CE Database subject headings: Tornadoes; Residential buildings; Natural disasters; Structural design. Author keywords: Tornado; Residential building; Natural hazard; Design method.