Optimum seismic design of steel bridge system with double i-type girders

Abstract

Recently in Japan, long span steel bridge systems with double I-type girders have been constructed for the reasons of reductions of construction cost and time of construction work, and simplicity of maintenance. This types of bridges have small numbers of girders, therefore, it is inherently difficult to determine the sizes of member elements, such as rubber bearing, RC pier and concrete pile foundation, so as to satisfy the ultimate performance constraints due to devastating earthquakes. In this study, the optimum design method is developed for the seismic design of steel bridge system with double I-type girders in which the design of experiments is successfully utilized in order to estimate the dynamic behaviours and sensitivities of the ultimate performance constraints with respect to the design variables. The optimum solutions of the heights of rubber bearings, cross-sectional dimensions and amount of steel reinforcements for RC piers and the detail of concrete pile foundation are determined by a classical branch and bound method. From the numerical example of five-span continuous steel bridge system with double I-type girders, it is emphasized that the optimum solutions can be obtained quite efficiently by the proposed design method. The effectiveness and efficiency of the optimum design method is also illustrated.