Experimental modal analysis of RC beams strengthened with SHCC subjected to shear under impact strain rates

Abstract

Strain Hardening Cement-based Composites (SHCC) holds great potential to be a remarkably effective material for shear strengthening of reinforced concrete beams in case of impact scenarios due to its great energy dissipation capability through the formation of multiple very fine cracks (∼100 μm of width). The effectiveness of this technique is investigated in the paper at hand through the observation of the changes in the dynamic properties in terms of natural frequencies, mode shapes, and damping ratios. Considering a non-destructive free vibration excitation of the specimens before the experiment (undamaged/intact state) to their condition after the destructive impact of an accelerated steel projectile. In this sense, two types of reinforcement configurations and two types of strengthening layers were investigated: reinforced concrete beams with and without stirrups were strengthened with SHCC made with polyvinyl alcohol (PVA) and ultra-high molecular weight polyethylene (UHMWPE) and tested under increasing levels of kinetic energy varying between 2.1 kJ and 6.4 kJ by using an accelerated impactor inside a drop tower facility. The parameter variation enabled conclusions with respect to the influence of the stirrup reinforcement and the SHCC strengthening contributions in the case of dynamic scenarios.