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Abstract This research investigates experimentally and analytically the effect of change in the transverse and longitudinal reinforcement ratio of Y-shaped reinforced concrete bridge piers on their torsional performance under seismic loading. The case of skewed alignment of piers typically present on horizontal curves of bridge deck is discussed. In the experimental program, seven specimens of bridge piers at a scale of 1:5 were tested. The longitudinal reinforcement ratios used in the research were 1.00%, 1.34%, and 2.09% while the volumetric ratios of transverse reinforcement were 0.40%, 0.70%, and 1.25%. The specimens were tested under horizontal cyclic quasi-static torsional loading with no vertical forces to represent earthquake with insignificant vertical acceleration. The specimens were loaded to failure which was manifested in the form of cracks spreading over the tested specimens. Deformations, strain in both longitudinal & transverse reinforcement, and crack pattern were recorded during the test on different loading stages. The top displacement and twist angle and their correlation with the change in longitudinal and transverse reinforcement, as theypresent the main seismic performance parameters of piers, were studied in order to quantify the loss of strength and stiffness degradation due to the torsional warping stresses. The energy capacity properties have been studied as well. In the second phase of the research, a comprehensive analysis of the tested specimens is conducted using computer finite element software and analytical results were compared with the experimental results and showed good agreement to variable levels. Also, different retrofitting schemes were adopted and modeled by computer software to predict the performance improvement and strength increase of test specimens and evaluate the efficiency and feasibility of retrofitting. The study highlights the importance of considering the seismic torsional demand in order to obtain an acceptable level of certainty in the field of design and strengthening of reinforced concrete bridge piers. |