Performance Based Design Approach for RC Square Bridge Columns under Combined Loadings Including Torsion

Abstract

Reinforced concrete (RC) bridge columns are subjected to combined bending moment, shear force, axial and torsional loads during earthquake excitations, particularly for skewed and curved bridges, and bridges with unequal spans or column heights. The combined loading would affect the seismic performance of RC bridge columns in terms of strength, stiffness, deformation and progression of damage limit states. Performance based design approach for RC square columns under combined loadings including torsion is investigated in this paper. Different damage limit states are evaluated from performance based design approach using proposed damage index model, which permits decoupling these combined actions according to the test data. The main variable considered in the experimental study is the ratio of torsion to bending moment (T/M). The effects of combined loading on the torsional and flexural hysteretic responses, plastic hinge characteristics, rotational and displacement ductility limits, progression of damage states are discussed. The progression of damage states, quantified according to the proposed damage index model, can be correlated to the observed damage from practical point of view, which exhibit reliable indication of failure stages of RC square bridge columns. Based on experimental and analytical results, progression of damage was found to be amplified by the effect of increasing torsion; and the displacement as well as rotational ductility is decreased due to the effect of combined loading. Hence it is necessary for the performance based design procedures to consider the effect of torsional loadings.