OPTIMUM DESIGN OF BOW-STRING GIRDER BRIDGE FOR RAILWAY LOADING

Abstract

Structural engineers, faced with the challenge of designing reliable structures at a minimum cost, continue to seek formal techniques to assist them in obtaining cost-optimal designs. A key feature of the design process is identification of alternative designs for solving the given problem., which is iterative and time consuming, and may involve the consideration of many alternatives. In case of arch bridge, options are thrust arch bridge & Bow string Girder Arch Bridge. Normal arches need high horizontal restrains from the foundation and may be uneconomic where such restraints are not present. Such problem is solved by introduction of Tie, which provide the horizontal restraint and bridge is known as Bow String Girder Arch Bridge. The economy of the steel Bow String Girder bridge superstructure, used extensively in medium and long span ranges, is affected by many factors such as the cost of material, dictated by the configuration, Rise of Arch, number of suspenders, shape and size of members, and cost of fabrication. Design of such structures is done in various software packages available and the Rise , Number of suspenders , shape and size of members for preliminary design is based on the experience of engineer and is mostly on the conservative side. However, with the use of parametric study involving different variables can be used to reduce the cost of the structure to great levels by optimizing the topology. Apart from cost, a significant amount of time can also be saved as the erection and fabrication required is less. The study presents the weight of structure, topology and standard cross-section optimization of steel Bow String Girder Bridge. The considered structures are consisted from deck (orthogonal stringers & cross-beams), which is connected to arch by mean of suspenders. A parametric Study is done with main focus on variables - span, rise & Number of suspenders. The proposed study minimizes the structure’s weight, determines the optimal topology with the optimal rise, number of suspenders as well as the optimal cross-sections of steel members.