Contribution to Optimizing Network Arch Bridges

Abstract

This work of research will tackle the development of an optimal structure for network arch bridges. The systematic employment of potentials to optimize these bridge structures will be examined for selected structural members. Suggestions for the construction of the bridge system and of selected details as well as basics for calculation and design will be developed. This paper will focuses mainly on the design of fatigue-proof hanger connections, statically efficient hanger networks as well as arches, which have a high load carrying capacity along with low material consumption. In order to provide sufficient security against fatigue failure for the decisive connections of the hanger bars, stress peaks that cause cracks have to be minimized and homogeneous stress distribution within the whole element has to be ensured. Initially, this paper will delineate an optimal solution for hanger connections by means of parameter-based shape optimization and subsequent topology adaptation. In the following, an analytic formula for the stress concentration factor of this connection will be developed in order to enable the application of the notch stress concept for hanger connections. To apply the static advantages of network arch bridges efficiently, the arrangement of the hangers is essential. In order to determine the most efficient hanger arrangement, five possible hanger arrangements with varying parameters (slope of the hangers, number of the hangers and span of the bridge) will be analyzed and evaluated with respect to systematically selected static criteria. On the basis of these investigations, recommendations for engineers how to choose an optimized hanger arrangement according to different geometrical bridge parameters will be made. Additionally, the constructive design of the arches and the upper wind bracing as well as the associated structural behavior are significant when an efficient network arch bridge is to be designed. For this reason, this paper will analyze the influence of the arch-shape, the arch-geometry and the arch-stiffness as well as the design and construction of other structural members on the stability of the arch. Based on these results, the constructive parameters will be optimized in order to reduce the steel weight of the arch without significantly reducing the load carrying capacity. Furthermore, the influence of different imperfections on the arch stability will be analyzed and the form and size of the decisive initial deflections emphasized. Finally, systematically selected examples will provide a comparison between the developed solutions and existing bridge structures in order to demonstrate the efficiency of the optimized structure.