Response mechanisms of reinforced concrete panels to the combined effect of close-in blast and fragments: An integrated experimental and numerical analysis

The effect of cased explosives on reinforced concrete components is important for the design of protective structures, since the interaction between the fragments and blast waves can modify or even amplify the damage caused. This work deals with the development of finite element analysis techniques to simulate the combined loading and to understand this interaction. In this work, an experiment conducted with a cased explosive and further tests from the literature were used together to develop and stepwise validate finite element analysis models of the different loading phases. The casing fragment velocities and spatial distribution were derived from explosive expansion simulations of the hull using the smooth particle hydrodynamics method together with a momentum conserving penalty contact. The blast loading applied on the concrete plate was based on established empirical formulae, acting at the same times as the fragments. Comparing the final damage with the experimental records revealed good agreement for most damage patterns. The model was used to identify the different damage evolution stages, such as shock-induced shear plug formation and subsequent structural dynamic bending with the associated damage. In addition, differential model variants with fragment and blast loading in isolation were simulated to resolve the response and damage of each loading component. The blast load caused predominantly bending deformations and damage, while the fragments caused similar cratering as seen in the combined case. However, the final combined damage was larger than that caused by each phenomenon. In the given situation, the fragments created most damage, but the established modelling approach opens the perspective to study these effects also for other ratios of explosive to casing weight and scaled distances, where the contributions might differ. Establishing a valid modelling approach is thus an important step towards more insight into the interaction of these complex loading types and damage effects.