Restoring-force model for reinforced concrete members failing in shear or bond after yielding

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The first objective of this study is to establish a restoring-force model for reinforced concrete members failing in shear after flexural yielding. Twenty specimens of reinforced concrete columns are tested under constant axial load. Test parameters were concrete strengths, amount of longitudinal and shear reinforcement, and the dimensions. Some of them had dimensions similar to actual columns, while the others had dimensions about a half of actual columns. Most of them failed in shear after cyclic inelastic load reversals. Piano wires were embedded in the specimens so that average transverse strains in the core concrete were measured. In some cases, core concrete strain was larger than several ten times of the strain in the transverse reinforcement. At the maximum deflection of some of the specimens, epoxy resin was injected. After the resin hardened, the specimens were unloaded. Then, CT scanning was conducted to obtain three-dimensional image of the cracks in each specimen. The results agreed with the measured strains in the core concrete. Such findings were utilized to propose a restoring-force model for reinforced concrete members failing in shear after flexural yielding.The second objective of this study is to establish a model for bond splitting failure in reinforced concrete. The specimen parameters include bar diameter, rib shape, cover thickness, and the presence/absence of confining reinforcement. The experimental results show that the size-effect is mainly attributable to brittle splitting cracks, and not to local crushing of concrete in front of the bar ribs. Based on this finding, we proposed equations that yield a large size effect for splices with small cover and short splice length, where brittle failure is expected. The proposed equations agree with both the experimental results presented in this study and the bulk of the experimental data reported in the literature.