Evaluation of ultimate strength and damage progress of strengthening RC beams using NSM technique under low-velocity impact loading

Abstract

This paper presents a thorough investigation concerning low-velocity impact load assessments and three-point bending tests conducted on reinforced concrete (RC) beams. These beams were strengthened using two separated methods CFRP sheets or GFRP rods through the Near Surface Mounted (NSM) strengthening technique. The impact load was generated by releasing a 150-kg steel projectile from a height of 100 cm. Additionally, the numerical analysis using Finite Element Analysis (FEA) was performed for further investigations. The current study assesses the influence of NSM reinforcement and loading types on the failure mechanism of the retrofitted beams. Both the impact resistance and the flexural capacities of the RC beams show substantial enhancements due to the integration of FRP reinforcement. However, concerning equivalent axial FRP reinforcement stiffness, GFRP rods exhibited notably more significant improvements in the flexural strength of RC beams compared to CFRP strips. The load-carrying capacity of the GFRP rod-retrofitted specimen increased by 24.71 % under the flexural progressive loading, while that of the retrofitted specimen with CFRP strips increased by 15.26 %. Similarly, regarding impact loads, RC beams retrofitted with NSM-GFRP rods have demonstrated superior performance compared to their NSM-CFRP reinforced counterparts. Under impact loading, the maximum mid-span deflection of the strengthened RC beams with GFRP rod and CFRP strips decreased by 40.01 % and 23.36 %, respectively. Furthermore, the failure mode of the NSM-retrofitted specimens was changed from flexural dominant failure to a combined flexural-shear failure in comparison to the reference beams. In the case of impact loading, although the FRP retrofitted beams experienced less damage under the same number of impact loads, the cracking patterns of the tested specimens were shown similar.