Shear Strength Prediction for Brittle Reinforced Concrete Member Considering Concrete Stress Conditions

Abstract eng:
The formula of ultimate shear strength of reinforced concrete members based on truss and arch mechanism is provided in design guideline by Architectural Institute of Japan and which shear design approach are specified in other countries’ code. The truss action is comprised of web tension reinforcements combined with a diagonal concrete compression field, and the arch action transfers shear corresponding to concrete stress in compression strut. The shear strength corresponding to web shear reinforcement ratio predicted by the combination of those actions gives feasible ultimate shear strength of beams. However, it is referred that predicted shear strength by the formula tends to overestimate the strength of reinforced concrete columns with low web reinforcement ratio, which show brittle failure. This may indicate that shear transfer mechanism formed in brittle members does not agree with the predicted failure mechanisms in the formula. In this study, to evaluate failure mechanism of brittle reinforced concrete members, concrete stress condition inside of the members was investigated by carrying out of experimental tests of specimen. The specimen simulates brittle reinforced concrete column which web reinforcement ratio is low. Geometric properties are the same in all specimens; cross section is 180mm×300mm; shear span length is 900mm; and shear span-to-depth ratio is 1.5. Concrete compressive strength and magnitude of axial load were selected as parameter. Cyclic loadings were applied to the specimen with constant axial load correspond to specified magnitudes. Triaxial strain gages were placed in the core of the cross section of columns to measure concrete’s strain. From the experimental test, concrete stress in the concrete core section at ultimate state was evaluated. Predicted Mohr stress circles drawn by measured strain depends on the axial load ratio and concrete strength. Factors associated with MohrCoulomb criterion was evaluated with experimental data, and shear strength prediction method was proposed on assumption that the brittle shear failure occurs when Mohr stress circle reaches Mohr-Coulomb criterion, which represents slip failure of concrete. The proposed shear strength agrees with experimental results, however, which gives underestimate strength for the brittle failure specimens with normal strength of concrete.

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