Behavior of RC Bridge Columns under Cyclic Flexural-Torsional Loadings with Moderate Shear

Abstract eng:
Reinforced concrete (RC) bridge columns are subjected to a combined flexural, axial, shear and torsional loading during earthquake excitations. This fact is particularly true for skewed and curved bridges, and bridges with unequal spans or column heights. This combination of geometrical irregularities with seismic loading can result in complex flexural and shear failure of RC bridge columns. An experimental study is being conducted to understand the behavior of RC circular columns under combined loadings. The main variables being considered are (i) the ratio of torsion to bending moment (T/M), (ii) the ratio of bending moment to shear (M/V), and (iii) level of detailing for high and moderate seismicity (low or high transverse reinforcement ratio). The results of four columns with low aspect ratio (height to diameter = H/D=3) tested under cyclic pure bending, cyclic pure torsion, and various levels of combined cyclic bending and torsion in the presence of moderate shear loading are presented in this paper. The effects of combined loading on the hysteretic load-deformation response, spiral and longitudinal reinforcement strain variations, and spalling/damage characteristics are discussed. Torsion-Bending interaction diagrams for tested columns are presented. Based on the test results, it is concluded that the flexural as well as torsional capacity is decreased due to the effect of combined loading and there is also a change in the failure mode and deformation characteristics. The experiments show that the torsional capacity does not change significantly due to the effect of moderate shear compared to the columns under low shear. However, there is a significant reduction in the deformation and energy dissipation capacity due to the application of moderate shear compared to the similar columns tested at low shear.

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