Strength analysis of buried curved pipes due to blast explosions

With the advent of new low-cost and powerful computers and explicit timeintegration FEM codes, three-dimensional models are now available for thetransient response analysis of buried structures due to blast explosions in theirproximity. In the industrial domain, a most interesting issue is to determine thecritical distance between the center of the explosion and the buried structure inorder to insure its integrity. In the present paper a systematic study is presentedon the stresses induced to buried pipelines, focussing on their curved parts suchas elbows and tees. In more detail, it was examined whether the curved parts of apipeline suffer more compared to the straight parts. For the purposes of thepresent study, the distance from the center of the explosion, the depth from theground surface and the impulse of the explosion are considered to be fixed. Onthe contrary, the shape of the pipeline is variable, as well as the relative positionof the pipeline with respect to the center of the explosion. The entire analysiswas based on a 3D explicit code (LS-DYNA, version 950). The main outcome ofthe study is that in all cases taken into account, the equivalent von Mises stressesexerted on the curved parts are either smaller or at most equal to those exertedon the straight parts of the structure. The numerical results lead to the conclusionthat for fast and safe decision making, the curved parts of a pipeline may beignored. Nevertheless, a more thorough investigation is required in order toextend this conclusion to other cases where the radius of curvature is differentthan the one chosen for the needs of the present study. Finally, the influence ofother parameters, such as the impulse characteristics, the soil layercharacteristics, the depth, the backfill etc, should also be further examined