Blast loading on square steel plates; A comparative study of numerical methods

Abstract

During the recent years, several promising finite element solutions have been presented for finding the response of structures subjected to blast loading. This thesis gives as a comparative study on 3 major solution strategies, and their implication on the response on constrained plates of varying standoff distances. The strategies chosen are the Lagrangian method using load blast function in LS-DYNA, in which the plate nodes are subjected directly to forces attained from empirical ConWep data. The Arbitrary Lagrangian Eulerian (ALE) method in LS-DYNA, where an initial charge is detonated within an air medium and impulse transferred through contact algorithms. Finally a particle method, where air and soil are treated as discrete particles. This novel approach gives faster calculations than the ALE method and possible more reliable results than the Lagrangian method.

Dharmasena et.al (2009) performed experiments where final deflection of steel plates was recorded for a charge off constant mass with varying standoff distances. These results were used to validate the models.

It was found that the Lagrangian analysis provided conservative results at short standoff distances, and very accurate predictions at greater distances.

An ALE analysis was performed under the same assumptions. Even though the analysis gave accurate final deflections at short standoff distances, it was found to be giving increasing impulse with standoff distance, for fine meshes. This resulted in increasing final deflection with standoff distance, which was unsupported by experimental data.

Finally, a discrete particle method has been applied using the IMPETUS code. It gave the most accurate prediction in terms of final deflections. It was found to give almost equal results as the ALE analysis for short standoff distances, and equal results as the Lagrangian analysis for the longer stand off distances. The computational times were also greatly reduced compared to the ALE method.