Compression behavior, strength, and ductility of confined concrete after inelastic tensile cyclic loading

In this investigation, confined concrete specimens were tested to study the effects of inelastic tensile cyclic loading of the longitudinal mild steel reinforcement embedded in a confined concrete core on the behavior, strength, and ductility of the confined concrete. Repeated inelastic tensile deformations of the longitudinal mild steel reinforcement bars inside the confined concrete core cause large cracks in the confined concrete. Whether these inelastic steel deformations and cracks in the concrete affect the compression behavior, strength, and ductility of the confined concrete is studied. The test specimens represent the critical confined concrete crushing height of the boundary zone confined concrete in a well-detailed reinforced concrete lateral-load-resisting wall. In this investigation, two identical 10 in. x 15 in. cross-section confined concrete test specimens were tested under two different ranges of quasi-static inelastic tensile cyclic loading. The first specimen was tested under increasing tensile cyclic loading up to 4 times the tensile yielding strain limit of the longitudinal mild steel reinforcement bars of the confined concrete core. Then, the specimen was failed under compression loading. The second specimen was tested under increasing tensile cyclic loading up to 16 times the tensile yielding strain limit of the longitudinal mild steel reinforcement bars of the confined concrete core. Then, the specimen was failed under compression loading. The test results for the two test specimens were compared to observe the effects of different levels of inelastic tensile cyclic loading of the longitudinal mild steel reinforcement bars inside the confined concrete. The test results were also compared with the theoretical results from previously developed confined concrete models under monotonic compression loading. These comparisons focused on the effects of tensile loading on the compression behavior, strength, and ductility of confined concrete under compression loading. The confined concrete compression behavior, strength, and ductility were similar for the two test specimens with the two different inelastic tensile cyclic loading ranges. The difference in peak compression strength was 4.5%. The axial force versus axial deformation curves for the two test specimens were similar. It was noted that after inelastic tensile deformation of the longitudinal mild steel reinforcement inside the confined concrete core, a compression load greater than the prior tensile load was required to close the cracks. In the inelastic tensile deformation load steps, the reversing compression strain in the reinforcement was small compared to the tensile strain. The compression stiffness and ductility of the confined concrete were not affected by inelastic tensile cyclic loading of the longitudinal mild steel reinforcement of the confined concrete core. There was a noticeable reduction in the compression strength of confined concrete. The peak compression strength of the confined concrete was smaller than the results of any of the theoretical confined concrete models that were considered.