Experimental and Numerical Evaluation of Rocking Column Bases With Friction Connections and Vertical Web Plates

Abstract

This paper investigates seismic performance of a low-damage steel rocking column base through experimental and numerical approaches. Asymmetric friction connections (AFCs) were designed at the column base with friction sliding parallel to the column flange. A pair of vertical web plates, which were shop welded to the shear keys then bolted into the foundation, were sandwiched the column web to restrain ultimate uplift and enhance the weak-axis performance. Quasi-static cyclic tests were conducted to investigate the as-built (INITIAL case), post-earthquake (AFTERSHOCK case) and immediate repaired (REPAIR case) performances in both strong and weak axes. It was found that with the presence of the vertical web plate, the moment resistance was increased by 10 % and 8 % for the strong and weak axes, respectively. The prying effect of vertical web plates well ameliorated the initial stiffness loss in the weak axis and can be more easily repaired to the as-built condition. A finite element (FE) model, verified by experimental results, was developed to quantitatively evaluate local plasticity, loss of AFC bolt pre-tension, and energy dissipation. Further analysis revealed the effect of the time-varying axial force on the hysteresis of rocking column base. In addition, in the weak axis, the axial shortening due to localized plastic deformation at flange tips led to a rocking interface with an arc edge and shifted the rocking pivot toward the column's neutral axis, thereby reducing rocking threshold and seismic performance.