Dynamic response of thin concrete slabs subjected to sequential projectile impact and blast loading: An experimental and numerical investigation

Concrete is a material universally found in critical infrastructure and protective structures where it may be exposed to both impact and blast loading. In this study, the response of concrete slabs subjected to sequential impact and blast loading is investigated experimentally and numerically. First, 50 mm thick slabs from three different types of commercially produced concrete with nominal unconfined compressive strengths of 35, 75, and 110 MPa were cast along with samples for material testing. After curing, ballistic impact tests were carried out using 20 mm diameter, 196 g mass, ogive-nose hard steel projectiles to emulate a projectile or fragment impact. Synchronised high-speed cameras measured the initial and residual velocities of the projectiles. After impact testing, the perforated slabs were exposed to a blast-like pressure load generated by a shock tube facility. Undamaged slabs were also blast tested as a reference. Quasi-static material tests were conducted using digital image correlation synchronised with force measurements. Finite element (FE) models for the combined loads were finally established in LS-DYNA, where the constitutive behaviour of the concretes was simulated by the Karagozian and Case (K&C) model. By comparison with the experimental results, the accuracy of the calibrated K&C model and the validity of the proposed FE models were demonstrated. Moreover, the effects on the structural resistance of two loading scenarios, sequential or simultaneous impact and blast loads, were numerically evaluated. It was found that applying the impact and blast loads sequentially may differ notably from simultaneous application.