Seismic performance of hollow bridge pier columns under multi-directional loading

High-strength concrete (HSC) offers the potential of enhancing flexure-shear displacement ductility capacity of reinforced concrete hollow bridge pier columns with highly reinforced boundary elements and slender wall webs exhibiting three-dimensional (3-D) inelastic web crushing shear failure mechanisms. In this study, the seismic performance of HSC bridge pier columns was evaluated through tests on two large-scale hollow pier column units subjected to a diagonal and a multi-directional cyclic loading protocol with design concrete compressive strengths of 34 and 138 MPa (5 and 20 ksi), respectively. Both test units exhibited ductile flexure-shear behavior until web crushing occurred at moderate ductility levels. The 3-D inelastic web crushing shear performance was evaluated based on test observations and the hysteretic force-displacement behavior along principal and diagonal directions. To evaluate the loading path effect on the inelastic web crushing shear performance specifically, the degradation of shear stiffness and energy dissipating capacity were quantified and compared with a two-dimensional (2-D) plane pier wall test. The comparable displacement ductility capacity of the two test units shows that HSC improves web crushing performance of the pier columns through smeared web concrete damage and shear stiffness degradation under multi-directional loading.