A 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 few minutes), and the intense and destructive forces imposed on engineered and non-engineered 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 EF4 tornado devastated a 0.8 km (1/2 mile) wide path almost 10 km (5.9 miles) long through the city of Tuscaloosa, Alabama continuing on the ground for 130 km (80 miles). 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 windspeeds and building occupant life safety in more damaging wind speed events such as EF4 and EF5 tornadoes. The philosophy articulates a design methodology that is the basis upon which structural engineering was formed, namely provide life safety and control damage, but focused at separate tornado intensity levels.Keywords: Residential building, Design method, Natural hazard, TornadoKeywords: Residential building, Design method, Natural hazard, Tornad

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 few minutes), 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 in more damaging wind-speed events such as EF4 and EF5 tornadoes. The philosophy articulates a design methodology that is the basis upon which structural engineering was formed—namely, provide life safety and control damage—but the new philosophy is focused at separate tornado intensity levels

Making the case for improved structural design : tornado outbreaks of 2011

A total of 1,625 tornadoes occurred in the United States in 2011, resulting in economic losses that exceeded $25 billion. Two tornado outbreaks stand out because they caused more than half of those losses. The tornadoes that cut through Tuscaloosa, Alabama, on April 27 and Joplin, Missouri, on May 22 were responsible for a combined 223 fatalities and more than 13,000 damaged buildings in the two cities. Although the economic losses associated with tornado damage are well documented, the writers argue that the overall impact should encompass longer term, broader considerations such as the social disruption and psychological effects that impact communities. This paper examines observations by tornado damage assessment teams led by the first author in these two medium-sized cities and suggests that the evolution of building codes and past approaches to construction have led to conditions that made this extent of damage possible. The authors outline a multidisciplinary path forward that incorporates engineering research and social and economic studies into a new design paradigm leading to building code changes and social practices that will improve resistance and mitigate future losses at a community level from tornadoes