DAMAGE AND RESTORING FORCE CHARACTERISTIC OF HIGH-STRENGTH REINFORCED CONCRETE BEAMS

For seismic design of high-rise RC structures, to secure safety against large-scale oceanic earthquakes and epicentral earthquakes and to enhance the damage controllability for repeated deformations over large numbers of repetitions owing to long-period ground motions, producing high-strength RC structures by using primary reinforcements with higher strength than the standard ones was considered to be effective. Furthermore, for seismic design of high-rise RC structures that are critical as social capital, in addition to examining the damage of a medium-scale earthquake and securing the safety against collapse/overturning to a large-scale earthquake, evaluating the seismic performance to a continuous input level and the performance design was required, to evaluate various performance requirements. On this basis, to realize high-strength RC structures, this study aimed to grasp the damage and to evaluate the skeleton curve of the high-strength RC beam and its hysteretic characteristics, such as hysteresis responses to repeated loading over several cycles, and to investigate the response of a high-strength RC beam subjected to cyclic loadings. Therefore, examinations aiming at clarifying the above-mentioned aspects were conducted using structural tests and analysis. First, to understand the effect of the cyclic loadings on the restoring force characteristics of the high-strength RC beams, structural tests were conducted and the effect on the restoring force characteristics was examined, such as strength deterioration owing to cyclic loadings. It could be confirmed that the maximum residual crack width after unloading- ductility factor relationship in high-strength RC members. Furthermore, examining the skeleton curve of the high-strength RC beams using high-strength primary reinforcement (USD 590, USD 685), it was found that the modified equation where a correction coefficient is multiplied by the calculation formula of rigidity lowering rate of the yield point for standard RC beams can evaluate the skeleton curve for the results of this test. Next, finite element analysis was carried out to reproduce and extend the understanding of the test results. The analysis results agree well with the test results. A parametric analysis was performed with the strength of rebar, tensile reinforcement ratio, and shear span ratio as a parameter. From the parametric study, the stiffness decreasing rate of the high-strength RC beams was examined. Finally, by comparing the r