Performance of RC Bridge Columns under Cyclic Combined Loading including Torsion

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Reinforced concrete (RC) bridge columns, specifically in the skewed and horizontally curved bridges, the bridges with unequal spans or column heights, and the bridges with outrigger bents, can be subjected to cyclic combined loading including axial, flexure, shear, and torsion loads during earthquakes. This combined loading condition would affect the performance of RC bridge columns with respect to strength, stiffness, deformation and progression of damage, and cause complex failure modes and in turn influence the overall behavior of the bridge system. This study performed experimental and analytical studies in order to investigate the performance of RC bridge columns under cyclic combined loading including torsion. The main variables considered here were (i) the ratio of torsion-to-bending moment (T/M), (ii) cross sectional shape, and (iii) transverse reinforcement configurations. The torsional and flexural hysteretic responses, plastic hinge formation, strength and stiffness degradation, rotation and displacement ductility limits, energy dissipation characteristics, and damage progression for these columns are discussed in this dissertation. A unified damage assessment approach was proposed to assess the damage limit states for RC columns under combined loading by unifying the decoupled damage index models for flexure and torsion. Moreover, a semi-empirical model was established to predict the interaction between bending, shear and torsional loads. It was found that the strength and stiffness degradation and progression of damage were amplified by an increase in torsional moment. The damage distribution and failure modes were affected by the combined loading effect. Also the square columns experienced more localized damage due to cross sectional shape and the transverse reinforcement configuration effect.

RC bridge columns, Cyclic load, Damage index, Ductility, Interaction, Cross sectional shape, Square, Oval