The process of transforming tornado damage intensity ratings into windspeeds is a critical step in the development of tornado windspeeds for engineering design. In order to achieve acceptable performance for tornado-resistant designs, the engineering framework for the analysis and design of structures (forward process) for specified tornado windspeeds and associated load effects should be consistent with the methods used for the estimation of windspeeds from damage (reverse process).
This paper illustrates how the results of engineering modeling/analysis of tornado simulated damage to single family residential houses can be used to estimate windspeed from damage observed in the field. We use Bayesian methods to develop probability distributions of engineering-based windspeeds given a field-observed DoD. The proposed method addresses many issues associated with the current deterministic mapping of EF DoDs to tight windspeed ranges: it is engineering based with a design-consistent analysis framework; it considers inherent variations in tornado wind loads and building position within the path; it considers variation in building practices/codes, and inherent variations in material/structural strengths; it includes significant differences in field-observable structural characteristics; it reflects uncertainties in non-observable structural details; and the method naturally considers overlapping DoD windspeeds. The method produces a progressive refinement in the tornado windspeed estimation process as more DIs are evaluated in the area of maximum windspeeds. Each additional DI adds more information to the process and may either sharpen or broaden the estimated windspeed distribution, depending on the level of consistency of additional observations/ratings. Single family homes were selected for analysis since they are one of the most frequently used DI’s to rate tornadoes in the EF scale and, also, there is a significant amount of field damage data and model validation on the performance of these structures in other wind storms.
The paper concludes with suggestions for improving the number of DIs and the DoDs used for single family homes in the EF scale. Comparisons are made of the windspeed distribution estimates with the current EF DoDs for single family homes vs. a refined set of DIs/DoDs developed in this research.