The Statistical History of US Tornadoes

As engineers, we all know that tornadoes are violent but rare wind events. Beginning with ASCE 7-22, limited tornado design appears in the code. But is there more to tornado design than “Basic Wind Speed” and “Exposure?” Let’s look at the historic records of US tornadoes, from the standpoint of probabilistic design, to see what we can learn about these devastating storms, common to much of our country. Just as earthquake damage involves more than acceleration and soil type, tornadoes have different sizes, duration, velocities, and these characteristics affect damage and risk to human life. We will address topics based on recorded tornado data: (1) How do tornadoes function? (2) Is the diameter of severe tornadoes larger or smaller than minor tornadoes? (3) Historically, how common are devastating tornadoes? (4) How can we build more tornado resistant structures for a reasonable economic cost? (5) What is the best method of protecting human life in tornadoes?