Experimental And Theoretical Investigation of Bridge Motion in Turbulent Flow

本课题对大跨度桥梁在湍动风激励下的运动稳定性和统计特性进行了试验和理论研究。对某航道设施中的桥梁断面模型进行了试验研究。通过适当地对模型进行比例调整来满足模型和原型之间的相似性要求，并通过将模型连接到位于水道外的气室中的重型气缸。当模型被编程为在给定的频率范围内以给定的模式正弦振动时，测量由结构运动引起的流体力。测量了耦合型力(如扭转运动引起的升力)和非耦合型力(如垂直弯曲运动引起的升力)。然后建立了桥梁运动的理论模型，考虑了这种实验确定的流体力产生机制，并计算了理论模型的运动稳定性边界和结构响应。最后，将理论预测与结构模型在特定平均速度和湍流级的流体激励下得到的另一组实验结果进行了比较。通过比较，为进一步完善理论模型提供了依据。还进行了流动可视化实验，以获得对结构-流体相互作用的基本认识。通过流动可视化获得的速度场为计算结构模型上的流体力提供了额外的手段。

Motion stability and statistical properties of the response of long-span bridges under turbulent wind excitations are investigated experimentally and theoretically in this project. Experimental investigation is conducted on bridge sectional models in a water-channel facility. Similarity requirements between a model and the prototype are met by suitably proportioning the model, and by connecting the model to heavy cylinders which are located in the air chambers outside the water channel. Fluid forces induced by the structural motion are measured when a model is programmed to oscillate sinusoidally in a given mode through a range of frequencies. Both the coupled type forces (e.g. lift induced by the torsional motion), and the uncoupled type forces (e.g. lift induced by the vertical bending motion) are measured. Theoretical models for bridge motion are then formulated to incorporate such experimentally determined fluid-force generating mechanisms, and motion stability boundaries and structural responses are computed for the theoretical models. Finally, the theoretical predictions are compared with another set of experimental results obtained when a structural model is excited by fluid flows of specified mean velocities and turbulence levels. The comparison provides a basis for further refinement of theoretical models. Flow visualization experiments are also conducted to gain fundamental insights into structure- fluid interaction. The velocity field obtained from flow visualization provides additional means for calculating the fluid forces on structural models.