Numerical study on perforation damage and fragmentation of reinforced concrete slab under close-in explosion

Reinforced concrete (RC) structure is prone to suffer localized damage when exposed to close-in explosions. Spalling damage might occur due to the reflected tensile stress wave exceeding the concrete dynamic tensile strength. When the blast wave is intensive enough, it can also cause significant crushing damage on the contact surface, potentially leading to perforation when the crushing depth aligns with the spalling depth. This perforation/spalling damage can generate a large number of secondary fragments with high ejecting velocities. Additionally, the blast wave might pass through the perforation hole and cause further acceleration of the secondary fragments. In the author's previous study, an ALE-FEM-SPH numerical model was established and validated with the existing testing data for the prediction of spalling damage as well as fragment sizes and velocities. As a continuous work, this study conducts numerical simulations to predict the perforation damage and fragmentation under higher-intensity blast loading. The results including centre perforation hole, spalling area on back surface, fragment ejecting velocities, fragment landing distance and fragment characteristics distributions are reported and studied. The acceleration effect on the secondary fragments by the traversed blast wave that further carries the fragments flying is also investigated. The numerical results show that using the scaled distance Z might not reliably quantify the perforation/spalling damage under close-in cylindrical TNT explosion. Given the identical scaled distance, the scenarios with different combinations of charge weight and standoff distance can result in large variations up to 300% in the predictions of damaged area and 50% for the maximum fragment ejecting velocities, respectively. A scaled blast parameter Z* is suggested and the empirical formulae are proposed for better quantification of the damaged area of RC slab as well as the fragment velocity and kinetic energy under close-in cylindrical TNT explosions.