Shear capacity enhancement of existing underground wall structures using postinstalled reinforcing bars

Existing underground structures constructed prior to the past few decades do not meet the present seismic design code; therefore, these structures do not have sufficient shear strength to withstand large-magnitude earthquakes and shear reinforcement is required. The reinforcement of these structures has not progressed due to the challenges associated with reinforcement methods. Thus, the authors propose a shear reinforcement method using postinstalled reinforcing bars to solve the previously mentioned problems. This method involves the insertion of reinforcing bars with mortar into drilled holes in reinforced concrete walls to achieve a shear bearing capacity similar to that of preinstalled stirrups. To verify the effectiveness of the method, several loading experiments on reinforced concrete specimens using monotonic and cyclic loads were conducted. This method provided a loading capacity that was 80% larger than the capacity provided by the preinstalled stirrups. Furthermore, finite-element analysis studies of the experimental specimens were performed by means of a nonlinear finite-element method not only to reveal the shear bearing mechanism but also to evaluate seismic performance.