During the construction of high composite steel-tube reinforced concrete bridge piers, the steel circular cylinders in a group are exposed to wind for a certain period. Under wind flow, the grouped cylinders have extremely complicated aerodynamic characteristics such as switching of the flow and mutual interference of vortex generation. In order to establish a rational wind resistant design for this type of structures, the aerostatic characteristics of a group of 9 cylinders (3 × 3) were extensively studied in a series of wind tunnel experiments under uniform as well as turbulent flows. As a result of the experiment, it is found that: (1) The drag coefficient that acts on the group is smaller than the one established according to present design standards and individual drag coefficients corresponding to each of the cylinders in the group are different. (2) For intervals of the cylinder group varying between 1.4-2.0 times the cylinder diameter, lift characteristics experience significant changes. In particular, the lift force reverses its direction for cylinder intervals of 1.4 times the diameter and 1.8 times the diameter and above. (3) Moment coefficients increase inversely with cylinder spacing and proportionally with turbulence intensity.
The effects of the shear level on the vortex shedding from a circular cylinder with its axis normal to the plane of the shear profile were investigated experimentally in the Reynolds number regime of 1.0×104 to 8.8×104. The experiments were conducted in a computer controlled multiple-fan wind tunnel, in which the velocity gradient of the linear shear flow could be altered easily. The normalized shear parameter, β, was varied from 0 to 0.3. It was found that the Strouhal number was not sensitive to the shear parameter, while the time-mean base pressure increased with the shear parameter and the root-mean-square magnitude of the base pressure fluctuations decreased with the shear parameter significantly.
A gust response analysis is vital for the design of long-span-suspended bridges. To obtain the precise results, new methods have been developed for the evaluation of aerodynamic admittances. This paper shows two methods using direct and indirect measurements. The former is to evaluate the ratio of wind fluctuations and the wind induced forces of a static rigid section model in a wind tunnel. The flow is turbulent and is made by a active gust generator. The latter is to evaluate flutter derivatives which have close relationship with aerodynamic admittance. Their algorisms are introduced and their results were confirmed by the experiments by the deck section of Kurushima 2nd Bridge.