Parametric study of seismic performance of structures with multiple rocking joints

• Published in: Engineering structures 2017-09, Vol.146, p.75-92
• Main Authors: Li, Tao, Berman, Jeffrey W., Wiebe, Richard
• Format: Article
• Language: English
• Subjects: Controlled rocking system; Earthquake construction; Earthquakes; Energy consumption; Energy dissipation; Higher-mode effects; Mitigation; Multiple rocking joints; Nonlinear analysis; Nonlinear response; Parametric statistics; Parametric study; Post-tensioning; Reinforcement (structures); Seismic activity; Seismic engineering; Seismic response; Shear; Shear stiffness; Steel; Steel frames; Steel structures; Stiffness
• ISSN: 0141-0296; 1873-7323
• DOI: 10.1016/j.engstruct.2017.05.030

•Modeling methods simulating rocking behavior used in previous studies are compared.•Parameters studied are selected to inspect behaviors of different rocking systems.•Higher-mode mitigation from multiple rocking joints are investigated.•The optimal locations for 2nd rocking joints are below the mid-height in most cases.•An additional third rocking joint helps control the structural responses. Research has demonstrated that base rocking lateral force resisting systems have excellent seismic performance which has resulted in their implementation in practice. However, such systems are limited in height because of force demands that are amplified by higher-mode effects. The use of multiple rocking joints, together with energy dissipation, has been proposed to mitigate higher-mode effects in rocking systems. Previous research has shown that placing a second rocking joint at the mid-height of a rocking steel braced frame, combined with the utilization of energy dissipation devices, is effective in reducing the effects of higher modes in rocking steel frames. Here, a parametric study using nonlinear response history analysis for a suite of earthquake ground motions is described that investigates the efficiency of higher-mode mitigation from multiple rocking joints and the optimal locations for second rocking joints. The parametric study is based on three prototype rocking steel frames of different heights. Other parameters studied were selected to investigate a wide-range of rocking system behaviors and include the energy dissipation level, flexural and shear stiffness of the frames, yield displacement of the energy dissipators, frame bay width, and post-tensioned bar type. Results suggest that placing a second rocking joint within the lower 22%–50% of the building height reduces the maximum story moment by approximately 10%–35% in different systems, and that energy dissipation provided at the second rocking joint is effective in controlling shear force. The interaction between changing specific parameters and the structural seismic performance is also revealed in this study. Finally, dynamic analyses of the 20- and 30-story prototype frames with 3 rocking joints reveals that a third rocking joint helps reduce the overturning moment slightly for the 20-story frames, while the reductions in overturning moment and shear force are more obvious for the 30-story frames.