Parameter Optimization of the Combined Viscous-Steel Damping System for Dual Vibration Control in Long-Span Suspension Bridges Under Traffic and Seismic Excitations

Hybrid damping systems are becoming increasingly popular in longitudinal vibration control of long-span bridges under various excitations such as traffic and seismic loads. However, their diversity and complexity make efficient parameter analysis challenging. This study proposes a simplification–equivalence–optimization (SEO) parameter design approach without time history analysis for the combined viscous-steel damping system (CVSDS), in which the vibrations induced by traffic loads and earthquakes are separately suppressed by the viscous fluid damper (VFD) and the steel yielding damper (SYD). The suspension bridge was simplified to a single-degree-of-freedom (SDOF) system, and the excitations were equivalently converted in the longitudinal direction. The SYD was optimized by stochastic seismic analysis and weighted Pareto optimization. Incorporating the stiffness effect of the SYD, the VFD was further optimized based on harmonic steady-state responses when considering train loads and stochastic responses when considering vehicle loads. Shake table tests were conducted to verify the feasibility of the structural simplification. Numerical time history analysis was performed to validate the proposed optimization approach and investigate the performance of the optimal damper. The results illustrate the efficiency of the proposed SEO method. The SDOF system provides an accurate reproduction of the longitudinal movement of the bridge girder. The optimal CVSDS significantly reduces structural displacement response. VFDs for resisting train loads are more powerful and nonlinear than those for vehicle loads. The initial stiffness of the SYD contributes the most to the vibration control capacity of the CVSDS under earthquakes.