Optimum post-tensioning cable forces of Mau-Lo Hsi cable-stayed bridge

Abstract

The Mau-Lo Hsi cable-stayed bridge, located in central Taiwan, is mainly composed of a particular steel pylons with a parabolic arch shape and twin steel girders on the plane of the Clothoid curve. Thirty-six cables were used and grouped into eighteen pairs, of which nine pairs were attached along the edges of each of the bridge decks connected to the pylon at two different concentrated zones. Restricted to the determined space coordinates at both ends of the cable, the lengths of the two cables of each pair are different. The superstructure of the bridge reveals an asymmetric two-span layout (119 m+59 m), so that appropriate post-tensioning cable forces are essential for improving the detrimental influence of the unbalanced loading due to the dead load on the deck. Therefore, the determination of post-tensioning cable forces is one of the most important issues for the practical design procedure. However, since the cable-stayed bridge is a highly statically indeterminate structure, the solution to the post-tensioning cable forces is not unique, making it difficult to explore the optimal structural performance. Restricted to practical limitations in the engineering field, the theory of minimum strain energy rather than the construction cost of the bridge was used in deriving the objective function as the quadratic form of the post-tensioning cable forces. In addition, the equality constraints for the restriction on the displacements of the pylon and the inequality constraints for the limitation on the envelopes of the cable forces are both implemented in the optimization model. The results obtained revealed that the method presented indeed leads to optimal structural performance for the Mau-Lo Hsi cable-stayed bridge in particular, and might be a useful reference for the design of other similar bridges.