Evaluating long-duration blast loads on steel columns using computational fluid dynamics

Abstract

Long-duration blasts are typically defined by positive pressure durations exceeding 100 ms. Such blasts can generate dynamic pressures (blast winds) capable of exerting damaging drag loads on comparatively slender structural components such as columns. With limited drag coefficient availability for specific structural geometries, Computational Fluid Dynamics (CFD) can be the only satisfactory approach for analysing blast loading on user-specified, finite geometries. The ability to analyse long-duration blasts with commercially available CFD programmes is still not confidently offered, with no prior studies examining the accuracy of modelling interaction with relatively much smaller, finite geometries. This paper presents a comparative investigation between numerical and experimental results to assess the predictive capacity of inviscid Eulerian CFD as a method for calculating long-duration blast drag loading on finite cross-sectional geometries. Full-scale long-duration blast experiments successfully measured surface pressure-time histories on a steel I-section column aligned at four orientations. Calculated pressure-time histories on exposed geometry surfaces demonstrated good agreement although reduced accuracy and under-prediction occurred on shielded surfaces manifesting as overestimated net loading. This study provides new understanding and awareness of the numerical capability and limitations of using CFD to calculate long-duration blast loads on intricate geometries.

Structural response of simple partially-clad steel frames to long-duration blast loading

“…For the partially-clad frames, a 90 o orientation initiated a greater response than a 45 o orientation. This was contrary to previous research on isolated steel I-sections [14,15], where UK Ministry of Defence © British Crown Owned Copyright 2021/AWE a greater peak displacement was observed at oblique angles due to a decreased inertia and increased projected area. Inclusion of cladding on the frames caused an increase in inertia at 45 o and an increase in projected area at 90 o , resulting in a greater response for the latter.…”

“…Denny & Clubley [14] showed that an isolated cantilever version of the same sized column as used in this study, subjected to a similar blast environment, experienced a maximum displacement in the X direction of 49mm at a 90 o orientation. Maximum displacement comparison between the columns in this study and Denny & Clubley's isolated cantilever allowed for frame interaction effects to be identified, discussed and quantified.…”

“…No accessible research has investigated the response of a steel frame in which the majority of elements are damaged by blast loading. Most literature investigating metallic structures subjected to long duration events considers only isolated column elements [11,12,13,14,15]. Of these studies, a number consider the effect of structure orientation on response, otherwise known as 'multi-axis effects'.…”

“…Of these studies, a number consider the effect of structure orientation on response, otherwise known as 'multi-axis effects'. Denny & Clubley [14] conducted experimental trials on steel cantilever I-section columns subjected to a blast load with peak overpressure, p + =55kPa and positive phase duration, t + =155ms at angles of 0 o , 30 o , 60 o and 90 o . Results…”

Frequency Bandwidth of Pressure Sensors Dedicated to Blast Experiments

“…Based on the analysis reported here, it can be concluded that it is not necessary to make a breakthrough to design ultra-wideband pressure sensors in order to accurately estimate the overpressure peak in the blast wave experiments reported in [ 19 , 32 ]. Available pressure sensors (see, e.g., [ 25 ]) can actually be used in such experiments.…”