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.
