Evaluation of progressive collapse alternate load path analyses in designing for blast resistance of steel columns

The alternate load path method is a convenient, “threat-independent” method used in progressive collapse analysis and design. Because no actual loadings are considered in this method, the resistance provided by the alternate load path method for specific extreme events is not well quantified. However, such quantification allows for an understanding of what real scenarios can be efficiently represented by alternate load path analyses. As blast loading is one of the abnormal loading events typically motivating an alternate path analysis, this load type is selected for evaluation in the present work. In order to find the blast threat that is representative of the alternate load path method in steel-framed buildings, finite element analyses of steel columns being subjected to blast loads were analyzed in the program LS-Dyna. Prior to this, sensitivity and validation studies were also completed, which are described herein. The results of the column analyses show that failure is governed by a stability-based deflection criterion. Conclusions regarding the charge sizes that the alternate load path method may be considered to be representative of, as well as the influence of column spacing, size, and end fixity on these results are given.