Experimental study on aerodynamic countermeasure for galloping vibration of stay cables attached with lamps: Perforated shrouds

Abstract

The aerodynamic countermeasure of the perforated shrouds is proposed to reduce the galloping vibration of stay cables installed with rectangular lamps. Ten test models with different parameters were designed and manufactured and a series of wind tunnel tests were carried out to measure the aerodynamic forces on the test models. Then, the mean aerodynamic force coefficients were obtained to further calculate the galloping force coefficients of these test models. Based on the quasi-steady theory, the effectiveness of the perforated shrouds on mitigating galloping vibration was verified by considering the effects of porosities, hole types, shroud diameter, the turbulence of approaching flow, and cable orientation (vertical and inclined). The cable inclination of 35° and a turbulence intensity of 9% was used for the force measurement wind tunnel tests, as well as shrouds with porosities of 0, 8.7%, 19.6%, 28.3%, 34.9%, 36%, 44.2%, and 49.0%. Two types of holes, including circular staggered and square array holes, were adopted, and two outer diameters of the perforated shrouds (125 mm and 88 mm) were used. The results show that the perforated shroud with a diameter of 125 mm plays an important role in mitigating the galloping vibration of both vertical and inclined stay cables with rectangular lamps. For the vertical test model, it seems that the optimal porosity of the perforated shroud is 19.6%, and the optimal porosity of the perforated shrouds for the inclined test model is within the range of 19.6%–34.9%. The minimum galloping force coefficients Cg of them is all greater than 0. The galloping critical wind velocity of the inclined cable-lamp structure without perforated shrouds is significantly lower than that of the vertical cable. However, the inclination of the stay cable induces a higher galloping critical wind velocity if the perforated shrouds are installed. The type of holes, a circular staggered and rectangular array, seems to not affect the galloping vibration. The turbulence intensity of 9% has a significant effect on the galloping critical wind velocity for the vertical and inclined cable attached with rectangular lamps without perforated shrouds but has little effect on the galloping critical wind velocity of the vertical and inclined cable-lamp system with perforated shrouds. The maximum value of combined aerodynamic mean force coefficients CC for the vertical test model with the perforated shroud is the same (1.1), the maximum wind load of the inclined test model with the perforated shroud is increased by 21∼58% due to the larger diameter.