Wind Loading Risks from Multivortex Tornadoes

Abstract

Multivortex (MV) windfields have recently been established as frequent characteristics of intense tornadoes, introducing new issues in tornado risk analysis and loading characterization. A potentially important issue in the quantification of MV loading characteristics regards the probability that a structure will be hit by one of these high velocity secondary vortices. Using a simple model of multivortex flows, analytic relationships have been derived to facilitate the calculation of multivortex tornado loading hit probabilities for structures and facilities. A numerical integration method as well as an approximate solution have been developed to compute the cycloidal areas traversed by secondary vortices. Example calculations using current estimates of MV parameters suggest the conditional strike probabilities for point targets within the intense windfield core region are about 0.4 for a continuous single secondary vortex. To estimate the total MV wind loading risks, these conditional probabilities are combined with estimates of multivortex frequency and tornadoe strike probability.