Reinforced　concrete　(RC)　piers　of　irregular　bridges　such　as　skew　or　curved　bridge　may　be　subjected　to　a　combination　of　axial　load,　shear　force,　flexural　moments,　and　torsional　moments　under　multi-dimensional　earthquake　excitations.　The　combined　loading,　particularly　the　torsion,　may　increase　the　possibility　of　irregular　flexural-shear　failure　of　RC　bridge　piers,　and　consequently　impair　the　seismic　resistant　capacity　of　bridge　structures.　To　investigate　the　effect　of　coupled　bending-torsion　actions　on　the　hysteretic　behavior　of　RC　circular　bridge　piers,　twelve　specimen　piers　was　tested　under　cyclic　combined　flexural　and　torsional　loadings,　and　then　the　effects　of　bending-torsion　action　on　torsion　and　flexural　capacity　of　RC　bridge　piers　are　evaluated.　Based　on　the　observed　and　measured　results　of　damage　characteristics　and　load-displacement　relationship　of　tested　specimens,　the　hysteretic　restoring　force　models　are　developed　to　predict　the　responses　of　RC　bridge　pier　under　combined　flexural　and　torsional　loadings.　The　result　shows　that　the　flexural　and　torsional　capacity　may　be　impaired　due　to　the　effect　of　bending-torsion　action,　the　failure　modes　and　deformation　characteristics　are　changed,　and　the　damage　zone　tends　to　move　upwards　form　the　typical　flexural　plastic　hinge　zone　due　to　the　effect　of　additional　torsional　moment.　The　proposed　empirical　flexural　and　torsional　hysteretic　model　for　circular　RC　bridge　piers　with　single　spiral　stirrup　can　very　well　predict　the　hysteretic　behavior　of　circular　RC　bridge　piers　under　combined　flexural　and　torsional　loadings.