Discrete optimum design of cable-stayed bridges

Abstract

Cable-stayed bridges are highly redundant structures in which the deck behaves like a continuous beam elastically supported by the inclined stays. They represent an aesthetically appealing and efficient structural solution for medium-to-long spans and are widely used all over the world. Their behaviour is governed by the stiffness of the load-bearing elements (pylons, deck and cable stays) and the cable force distribution. The structural design of cable-stayed bridges is iterative process in which designers have to satisfy all criteria’s relating to safety, use, economy, by changing certain structural parameters. In case of cable-stayed bridges the design of bridge includes solving a lot of different problems such as the choice of structural system, nonlinearity, construction process, dynamic behaviour, etc. Project of such structures generate massive amount of information during analysis and design process. The optimization algorithm can include as design variables mechanical, geometrical and sectional properties. Thus, they can be used in design process to allocate cross-sections of structure elements and/or determine the prestressing forces of cables to obtain optimal length and height of towers and spans. Most of the methods for the optimum design of engineering structures make the assumption that member size variables are continuous. Generally, designers are restricted to choosing member sizes from a discrete set of commonly available sizes and this problem is solved here. The rigorous discrete optimum design is a NP-hard problem (exponential time vs polynomial time for continuous optimization) significantly more difficult than the continuous problem. In this work it is presented structural analysis and discrete optimization of concrete cable-stayed bridge. As optimization method is used segmental optimization method to obtain optimal dimensions of deck and tower cross-section and adjustment cable forces.