Analytical Assessment of Main Cable Shape for Three-Pylon Suspension Bridge with Unequal Main-Span Lengths: Thermal Effect Consideration

Abstract

Three-pylon suspension bridges with unequal main-span lengths are terrain-adaptive, and this feature makes them suitable for broad applications. However, the design and construction control of such bridges requires an accurate assessment of the main cable shape. In this study, an analytical approach for shape finding of the main cable is proposed within the framework of multisegment catenary theory. For the determination of the sag∶span ratio of the secondary main span and the height of its side pylon, the basic principles were formulated. These imply that the elevation of the lowest hanging point of the main cable in the secondary main span should be equal to the main cable elevation at the midspan point in the main span. An analytical algorithm for estimating the thermal effect on the shape of the main cable was presented. Given the intermediary role of pylon top displacement and rotation angle of the splay saddle, a set of simultaneous equations was established and solved for all spans under three conditions: closure of elevation difference, moment equilibrium of splay saddle, and conservation of the unstressed length of the main cable. The proposed method was applied to a three-pylon suspension bridge with unequal spans of 248+1,060+1,360+380 m. The results obtained proved the feasibility and efficacy of the proposed approach. The application of these principles made it possible to reduce the height of the side pylon on the side of the secondary main span. This not only reduced the material consumption of hangers in the secondary main span but also improved the overall appearance of the bridge. Further analysis of the thermal effects revealed a linear correlation between the structural deformation and temperature variation. Span length variation caused by the bending deformation of pylons was shown to have a significant impact on the temperature sensitivity coefficient of the main cable elevation. This impact can be counteracted by the thermal contraction/expansion in the left and right side spans, whereas the superposition of both effects occurs in the main and secondary main spans.