Study of Cyclic Performance and Design Method of UHPC-NSC Composite Pier

The composite pier, which consists of ultra-high-performance concrete (UHPC) and normal strength concrete (NSC), is a promising option for practical engineering due to its remarkable mechanical performance. However, the cyclic behavior and seismic design mechanism of the composite pier have not been thoroughly investigated. This paper aims to study the cyclic performance of the composite pier by conducting cyclic tests on 10 specimens. The thickness of the UHPC tube, strength of reinforcement, spacing of stirrups, and other parameters are considered. The crack distribution, hysteretic response, and failure modes are observed and analyzed. Results show that the composite pier exhibits good crack-control ability, large bearing capacity, and effective energy dissipation. The expansion of the inner NSC may exacerbate the buckling of the UHPC tube, thus leading to more severe seismic damage. To further investigate the composite pier, a numerical model is established to analyze the optimal thickness of the UHPC tube. The ultimate state of the composite section is taken into consideration, and the upper and lower limits of the height of the compression zone are proposed. Based on the parametric analysis, a recommended range of the UHPC tube thickness is derived.