RC structure sometimes suffers from internal defect caused by inferior construction or from internal damage caused by deterioration. In this study, post-peak behaviors of those beams were investigated both experimentally and analytically. The rock pocket was simulated in RC beams as an example of internal defects. The deterioration of concrete strength and Young's modulus, and breaking of lateral confinement caused by alkali-silica reaction (ASR), were simulated as examples of internal damages. The results of this study can be summarized as follows; The rock pocket and breaking of hoop tie deteriorate mechanical performances of RC member in post-peak region. The deterioration of mechanical performance was caused by the decrease in lateral confinement and can be simulated by changing the gradient of strainsoftening curve in strain-softening constitutive model of concrete.
