Model for calculating local bearing capacity of concrete with spiral stirrups

This study evaluates the mechanical and failure modes of 30 concrete specimens under local compression. The experimental results indicate that the specimens undergo three types of local compressive failure modes. These modes primarily depend on the strengths of the tensile and compression regions. Based on the test results, a calculation model for the local bearing capacity of concrete with spiral stirrups Fl is formulated. In the model, the local compressive failure of concrete with spiral stirrups is classified into tension and compression. The yielding of spiral stirrups in the tensile region is regarded as tensile failure, and compressive failure is considered to have occurred when the strain value in the compression region reaches 0.002. To simplify the model calculation, the spacing s, diameter d, and yield strength fy of spiral stirrup as well as the local compression area ratio Ab/Al (ratio of the concrete bearing area Ab to the loading area Al) are comprehensively analyzed. Based on the analysis results, a formula for the bearing capacity of the reinforcement Ns is derived. The independent variables of the formula are yield force of spiral stirrup fyAssl, stirrup spacing s, and ratio of specimen side length to loading plate side length h/a. A simplified formula for calculating the tensile failure of the specimen is derived. To ensure simultaneous tensile and compressive failures, a critical reinforcement ratio of the spiral stirrup ρvu is proposed based on the calculation model. Test data from similar axial local compression tests are collected to verify the accuracy of the calculation model. The local bearing capacity of concrete is recalculated according to the calculation method proposed in this study. Results show that the calculation model is highly accurate. Accordingly, it may be used as reference for calculating the local bearing capacity.