Asymmetric Arrangement of Crossed Cables in Multitower Cable-Stayed Bridges Based on Structural Stiffness

Abstract

To increase the structural stiffness of multitower cable-stayed bridges, an analysis theory of crossed cable is developed, and a new-layout scheme of crossed cable for the multitower cable-stayed bridges is presented. The area ratio of the crossed cables at the same anchorage position was derived by examining their restraint stiffness to the bridge tower. Accordingly, the anchorage position of the crossed cable on the main span with a maximum restraint stiffness was examined, and an asymmetrical arrangement of the crossed cables on the main span was proposed. The finite-element models of three- and four-tower cable-stayed bridges were established. The influences of the asymmetrical arrangement of crossed cables on the deformation of the tower and girder, the stress of the bridge tower, and the dynamic characteristics of the bridge were analyzed. The results from the analysis demonstrate that the area ratio of crossed cables is equal to the ratio of the square of the cable length when their restraint stiffness is maximum. When the height–span ratio of the multitower cable-stayed bridge was between 0.2 and 0.3 and the anchorage position of the crossed cable was 0.69–0.73 times the span length from the middle tower, the restraint stiffness of the crossed cables was maximum. Under a uniform live load, the mechanical properties of asymmetrical arrangements were better than those of the symmetrical arrangement of crossed cables. When the crossed cable as adjusted to an asymmetrical arrangement for three- and four-tower cable-stayed bridges, the tower top displacement and tower bending moment were considerably reduced, and the vertical frequency of the bridge was increased. Note that the asymmetrical arrangement could considerably improve the restraint of crossed cables to the middle tower, increase the structural stiffness of the bridge, and improve the stress of the middle tower.