Analytical and Numerical Investigation of Frequency-Independent Tuned Inerter Outrigger Systems for Seismic and Wind Vibration Control of Tall Buildings

Abstract The increasing construction of tall and slender buildings has intensified the need for passive vibration control systems for mitigating structural responses under seismic and wind excitations. Conventional damped outrigger systems are generally tuned to dominant vibration modes and exhibit reduced effectiveness under broadband dynamic excitations involving significant higher-mode participation. This study presents a comprehensive analytical framework for two frequency-independent passive outrigger systems, namely the Frequency-Independent Tuned Inerter Damper Outrigger (FI-TIDO) and the Frequency-Independent Negative Stiffness Damper Outrigger (FI-NSDO), for multimodal vibration control of tall buildings. Closed-form analytical formulations are developed to characterize the equivalent dynamic behaviour of the proposed systems, while a numerical optimization procedure determines their optimal design parameters. By integrating frequency-independent hysteretic damping with inerter and negative stiffness mechanisms, the proposed configurations provide broadband vibration mitigation without tuning to a single structural frequency. Their performance is evaluated on a benchmark 60-story building subjected to seismic and crosswind excitations using frequency-domain and nonlinear time-history analyses. Results show that the proposed frequency-independent outrigger systems substantially enhance modal damping and vibration mitigation over a broad frequency range. The FI-TIDO system achieves a maximum first-mode damping ratio of 24.32%, compared with 2.89% for a conventional damped outrigger system, and reduces the average inter-story drift and floor acceleration by 32.5% and 23.45%, respectively, under eleven near-fault earthquake records. The developed analytical framework provides an efficient tool for the analysis, preliminary design, and optimization of advanced frequency-independent outrigger systems for tall buildings subjected to broadband seismic and wind excitations.