Truss modeling of as-built and CFRP-repaired RC bridge columns subjected to combined cyclic lateral loading and torsion

Under design level earthquakes, reinforced concrete (RC) bridge columns subjected to combined lateral and torsional loadings have been shown to behave considerably different from bridge columns subjected to lateral loading alone. This is caused by the interaction between lateral and torsional loadings. Thus, modeling of RC columns under combined loading including torsion has been a focus in the recent literature. However, very few techniques have been reported on the use of general finite element software to simulate these columns under cyclic loadings. To fill in this gap, this study employed a truss modeling technique to simulate the response of RC bridge columns subjected to a constant axial compression and reversed cyclic lateral loading including torsion. The column was modeled as a three-dimensional truss composed of longitudinal, transverse, and diagonal truss elements to represent the contributions of longitudinal reinforcement and/or concrete, transverse reinforcement, and diagonal concrete struts to the global behavior of the column. A parametric study was conducted to determine the inclination angle and thickness of the diagonal struts in the truss model to properly predict the behavior of the column. The analysis results of three unstrengthened (i.e., as-built) RC columns and two columns that were repaired with carbon fiber reinforced polymer (CFRP) jackets were compared with experimental results of the corresponding columns, which showed both the efficiency and accuracy of the proposed modeling technique in terms of stiffness, strength, deformation, and energy dissipation.