Seismic Performance of UHTCC Short Columns Reinforced with Negative Poisson’s Ratio Steel Rebars as Stirrups

The ductile seismic design of engineering structures is underpinned by materials with high ductility and superior energy dissipation capacity. Negative Poisson’s ratio (NPR) steel rebar, a novel auxetic steel reinforcing material exhibiting a negative Poisson’s ratio effect alongside high strength and ductility, offers promising potential for such applications. In this paper, quasi-static cyclic loading tests were conducted on six ultra-high toughness cementitious composite (UHTCC) short column specimens with varying stirrup materials, stirrup ratios, and axial load ratios to investigate the seismic performance of UHTCC members reinforced with NPR steel rebars as stirrups. A systematic evaluation was performed focusing on failure modes, hysteretic behavior, deformation capacity, stiffness degradation, and energy dissipation characteristics. In addition, the strain evolution behavior of steel reinforcement was analyzed. The results demonstrate that replacing HRB400 rebars with NPR rebars has a significant enhancement in seismic performance. Specifically, shear capacity (by 19.87%), ductility (by 1.82%), plastic deformation (by 18.09%), ultimate drift ratio (by 14.75%), and energy dissipation (by 10.46%). The unique uniform axial deformation characteristics of NPR steel rebars resulted in the stirrups exhibiting comparable strain levels in both directions perpendicular and parallel to the lateral loading direction. Furthermore, the use of NPR steel rebars delayed yielding of the HRB400 longitudinal rebars, and the yield displacement of the NPR-reinforced specimen N-100-0.3 increased by 12.35%. This study presents a pioneering investigation into the seismic performance of UHTCC short columns reinforced with NPR steel rebars, yielding significant insights into their structural behavior. The innovative combination of NPR rebars and UHTCC materials offers a novel approach for achieving ductile seismic design in short column applications.