Rocking damage-free steel column base with friction devices: design procedure and numerical evaluation

摘要

Earthquake resilient steel frames, such as self-centering frames or frames with passive energy dissipation devices, have been extensively studied during the past decade but little attention has been paid to their column bases. The paper presents a rocking damage-free steel column base, which uses post-tensioned (PT) high strength steel bars to control rocking behavior and friction devices (FDs) to dissipate seismic energy. Contrary to conventional steel column bases, the rocking column base exhibits monotonic and cyclic moment-rotation behaviors that are easily described using simple analytical equations. Analytical equations are provided for different cases including structural limit states that involve yielding or loss of post-tensioning in the PT bars. A step-by-step design procedure is presented, which ensures damage-free behavior, self-centering capability, and adequate energy dissipation capacity for a predefined target rotation. A 3D nonlinear finite element (FE) model of the column base is developed in ABAQUS. The results of the FE simulations validate the accuracy of the moment-rotation analytical equations and demonstrate the efficiency of the design procedure. Moreover, a simplified model for the column base is developed in OpenSees. Comparisons among the OpenSees and ABAQUS models demonstrate the efficiency of the former and its adequacy to be used in nonlinear dynamic analysis. A prototype steel building is designed as a self-centering moment-resisting frame with conventional or rocking column bases. Nonlinear dynamic analyses show that the rocking column base fully protects the first story columns from yielding and eliminate the first story residual drift without any detrimental effect on peak interstory drifts. The study focuses on the 2D rocking motion, and thus, ignores 3D rocking effects such as biaxial bending deformations in the FDs. The FE models, the analytical equations, and the design procedure will be updated and validated to cover 3D rocking motion effects after forthcoming experimental tests on the column base.