Investigating multi-axis long-duration blast response of steel column sections

Long-duration blast waves are typically defined by positive pressure durations in excess of 100ms and are characteristic of very large explosive events. Such blasts generate substantial impulse and dynamic pressures (blast winds) that considerably exceed shorter duration blasts with the same peak overpressures, which are particularly damaging to drag-sensitive structural elements such as steel columns. A number of recent large-scale industrial accidents have highlighted the potential for multiple detonations to occur that can cause long-duration blasts to successively interact with structures, and constituent column elements from different axes. This research investigates and quantifies blast loading, structural dynamic response and resulting damage states of steel column elements subjected to both single and multiple (successive) long-duration blasts. Primarily, this research examines the influence of multi-axis interaction and the effect of prior column damage on subsequent structural response, given the case of multiple detonations. Ten full-scale long-duration blast trials were conducted, testing steel I-section and square hollow section (SHS) columns aligned at different orientations to the blast to examine the influence of multi-axis interaction. Six trials also investigated the effect of prior column damage on subsequent structural response and damage accumulation by subjecting SHS columns to three successive blasts. Analysis of results revealed a clear relationship between blast loading, column mechanical properties and magnitude of structural response as a function of section orientation to the blast, thus demonstrating that multi-axis interaction has significant influence. Columns aligned at oblique orientations to the blast exhibited larger structural responses and higher loading due to increased projected area and drag coefficient providing evidence to question the validity of existing simplified blast loading characterisation methods. Column response to multiple blasts generally exhibited reduced structural resistance, with damage accumulation influenced by local residual stress states, load direction symmetry and sequencing. This research also examined uncoupled computational models of multi-axis blast loading and structural dynamic response of steel columns using computational fluid dynamics (CFD) and finite element analysis (FEA) respectively. Comparisons with experimental data have shown reasonable levels of agreement, indicating potential to provide future predictive capacity