Damage assessment of square RC bridge columns subjected to torsion combined with axial compression, flexure, and shear

Reinforced Concrete (RC) bridge columns can be subjected to combined flexure, shear, axial and torsional loadings under multidirectional earthquake motions and significant vertical motions, specifically in skewed and curved bridges, bridges with specific structural restraints, and bridges with unequal spans or column heights. This paper presents experimental and analytical studies to assess the damage progression of square RC bridge columns under combined loadings including torsion. The main variable in this study is the ratio of Torsional-to-bending Moments (T/M). The effects of combined loadings on the torsional and flexural hysteretic responses, strength, plastic hinge distribution, and progression of damage states are highlighted in this paper. A unified equivalent damage index model is proposed to couple the flexural and torsional actions for combined loadings. Quantified damage indices value under combined loadings can be correlated to the categorized damage states from a performance-based point of view. Based on the experimental and analytical results, the progression of damage was found to be amplified by the torsion effect, and the rotational ductility was decreased due to the effect of combined loadings.