大跨桥梁阻尼伸臂消能体系减振机理与设计优化

项目简介

Long-span bridges have low structural damping and low and closely-spaced frequencies. Hence, under low-speed wind conditions, they can experience large-amplitude vortex-induced vibrations which jeopardize the bridge serviceability and long-term structural safety. This project proposes a girder-rotation-based concept for multimode vibration mitigation of long-span bridges, along with a practical realization using damped outriggers – an outrigger is installed on the bridge girder near a bridge pylon or a pier to transform girder rotations during bridge vertical vibrations to horizontal displacements of the outrigger at its end. Horizontal dampers along the longitudinal axis of the bridge are installed between the outrigger end and the pylon/pier to dissipate vibration energy. As compared to existing bridge vibration control methods that are based on girder vertical displacements, one damped outrigger can improve multimode damping and the horizontal dampers can absorb and suppress the girder longitudinal deformation induced by thermal effects. The damped outriggers can reduce both wind-induced vibrations and seismic responses of the bridge and thus the traditional dampers between the bridge girder and pylons/piers are no longer necessary. The project will focus on long-span suspension bridges. Both simplified analytical models and refined finite element models will be used to examine the effects of structural and damped outrigger parameters, boundary constraints and coupled vertical-longitudinal girder vibrations on the damping performance, wind-induced vibrations and seismic responses of a suspension bridge with damped outriggers. By this means, the vibration mitigation mechanism of the proposed system will be understood. Subsequently, approximate explicit design formulas and universal optimization procedures will be developed for the design optimization of long-span bridges with damped outriggers. Ultimately, a systematic design principle to achieve high-damping for long-span bridges will be formulated. At last, a model of a suspension bridge with damped outriggers will be established and tested to validate the proposed vibration mitigation system for long-span bridges and the corresponding design optimization theory. The outcome of the project could provide a stable and implementable solution for vibration control of vortex-induced vibrations of long-span bridges, and hence the proposed study is of both scientific and practical significance.