Blast response of retrofitted reinforced concrete hollow core slabs under a close distance explosion

•Externally bonded reinforcement (EBR) are an efficient technique to upgrade the blast resistance of the hollow core slabs.•Under a close distance explosion, the propagation of the blast wave through the concrete cause a longitudinal crack in the critical zone where the ribs of the hollow cores have the smallest thickness.•The longitudinal crack extending into a vertical crack trigger local initiation of debonding between the carbon fiber reinforced polymer (CFRP) and the concrete. This article discusses the blast response of reinforced concrete hollow core slabs (RCHCS) with a topping layer subjected to a close distance explosion and investigates the efficiency of carbon fiber reinforced polymer (CFRP) as externally bonded reinforcement (EBR) in order to improve the blast resistance of the slabs. Three simply supported RCHCS with a topping layer are subjected to an explosion of 1.5 kg of C4 suspended at mid-span, underneath the slabs at a standoff distance of 0.5 m. One of the slabs is used as a reference specimen and the two remaining ones are retrofitted with different amounts of CFRP. A numerical analysis is also carried out using the finite element (FE) software LS-DYNA to complement the experimental results of the blast campaign. The results indicate that bonding CFRP strips on the surface opposite to the explosion is an effective way to reduce the mid-span deflections and to limit the damage levels in the slabs. A reduction of 16% and 30% in the maximum deflection is recorded for the RCHCS retrofitted with 2 strips and 4 strips, respectively. Longitudinal cracks between the voids are observed on the lateral sides of the slabs due to the propagation of the blast wave through the concrete. These longitudinal cracks, extending with a vertical crack, trigger local debonding between the CFRP strips and the concrete during the explosion. Maximum deflections and crack distribution predicted by the numerical analysis are in a good agreement with the experimental results.