Developing a new procedure for evaluating the ductility capacity of rectangular RC piers subjected to biaxial flexural loadings

The ductility capacity of bridge piers is estimated uniaxially by moment-curvature analysis, regardless of the amount of flexural demand on the perpendicular axis of the section. In this study, by applying a numerical fiber-based model, the ductility capacity of reinforced concrete (RC) piers subjected to biaxial monotonic loadings is investigated. 288 RC cantilever columns with 6 different square/rectangular solid/hollow sections are studied. Variations in shape, aspect ratio, dimensions, axial compression force, concrete characteristic strength and longitudinal reinforcement ratio are considered in the defined samples. Monotonic biaxial displacement demand is applied at the top of the cantilever columns. Different monotonic displacement paths are defined by varying the angle between the loading alignment and the major axes of the section. In order to sum up and interpret the responses obtained from different samples, a framework is developed to derive normalized ductility capacity ratios (RΔ). Based on the findings in this study, the maximum reduction of the mean ductility capacity ratio (RΔ‾) is about 15% and 8% for solid and hollow rectangular RC sections, respectively. According to the obtained results, the maximum reduction of ductility capacity of square and rectangular sections occurs when ϕ angle is between 40°-50° and 50°-70°, respectively. Based on the obtained mean ductility capacity ratios (RΔ‾), a bi-linear equation is proposed for evaluating the ductility capacity of rectangular RC sections under biaxial flexural demands.