Dynamic behaviors of steel multiple-rocking-column system with varying post-rocking stiffness

Abstract

Ancient wooden pagodas have shown remarkable seismic resistance, surviving strong earthquakes over millennia. This impressive performance is credited to the unique seismic mitigation and isolation mechanism. The discontinuity between the timber columns allows each story to rock freely like a “balancing toy”, effectively reducing inertia forces. Inspired by this fascinating phenomenon, an innovative steel multiple-rocking-column system (MRCS) has been designed. This system includes continuous beams, discontinuous columns, and springs. The post-rocking stiffness of the MRCS can be adjusted to be positive, quasi-zero, or negative by varying the stiffness of the springs. This paper mainly focuses on the effects of post-rocking stiffness on the dynamic behavior of the MRCS, both theoretically and experimentally. Initially, analytical models were developed to assess the stiffness properties of the MRCS. After that, a scaled MRCS model consisting of three stories and featuring seven different post-rocking stiffness levels was designed. Shaking-table tests were conducted to investigate the dynamic response of the model under seismic excitations. The equations governing the post-rocking stiffness of the MRCS demonstrated good accuracy with test results. As the post-rocking stiffness decreased, displacement response increased gradually but significantly mitigated horizontal acceleration responses along the structural height. Wavelet transform-based time-frequency analysis provides a comprehensive understanding of the dynamic features of the MRCS. Furthermore, a finite element model was established to verify the proposed theoretical model, and the numerical results agree well with the experimental findings. This study provided valuable insights into the design of innovative multiple-rocking systems for post-rocking stiffness.