Capacity Design of Reinforced Concrete Framed Building for Earthquake Loading

Background: The capacity design philosophy permits ductile components of a structural system to yield, whereas the brittle components are not permitted to fail. Therefore, brittle components should have sufficiently higher strength compared to ductile components. The “strong-column / weak-beam” design philosophy ensures good ductility and a preferable collapse mechanism in the building. The failure mode wherein the beams form hinges is usually considered to be the most favourable mode for ensuring good global energy-dissipation without much degradation of capacity at the connections. In order to ensure this favourable failure mode design codes recommend a minimum value of Moment Capacity Ratio (MCR). Methods: MCR is defined as the ratio of cumulative column moment capacity to cumulative beam moment capacity framing to a particular joint. Calculation of MCR is complicated as the column bending strength varies with the axial load. A family of RC framed building models is analysed in this study for earthquake load considering various load combinations given in relevant Indian standards. A range of axial force that may arise in the column sections during an event of design earthquake are obtained. Findings/Applications: A simplified procedure to calculate MCR empirically is proposed. The proposed method is computationally simple for calculating nominal design strength of the column to be used in determining MCR at a beam-column joint.