Effect of shear reinforcement and external strengthening with strain-hardening cement-based composites (SHCC) on the impact resistance of reinforced concrete beams

The paper presents a series of impact experiments performed on reinforced concrete (RC) beams with and without stirrups and additionally without and with lateral strengthening layers made of two types of strainhardening cement-based composites (SHCC). The impact tests were performed in an advanced drop tower facility with accelerated steel projectiles. Four impact velocities were applied, ranging from 17 m/s to 30 m/s, corresponding to kinetic energies from 2.1 kJ to 6.4 kJ. The difference among the 20 mm-thick, normal-strength SHCC layers with 2 % fiber volume content consisted in the type of reinforcing fiber: polyvinyl alcohol (PVA) or ultra-high molecular weight polyethylene (UHMWPE). The RC beams with no shear reinforcement yielded shear failure with displaced punching cones under all impact velocities. The stirrups notably increased their impact resistance and damage extent, allowing multiple impact loads without structural collapse. The lateral strengthening layers of SHCC substantially increased the load-bearing capacity, diminished the damage extent, and increased the damage tolerance under repeated impact events of the RC beams both with and without stirrups, proving to be a promising strengthening solution for existing structures prone to severe mechanical loading.