In this dissertation, transverse section optimization of reinforced concrete box-girder bridges is introduced on the basis of the results of finite element analysis with 6 DOF per node flat shell element. For structural optimization, a simple, yet effective, algorithm is used. Instead of utilizing a more sophisticated mathematical model that deals with many design variables and complicated descriptive functions, the introduced algorithm performs a direct search of the section database to reach to an optimum solution. After constructing the database of predetermined R/C sections which are arranged in order of increasing nominal strength of sections, the relationship between the section identification numbers and the resistant capacities of sections is established by regression and used to obtain and initial solution(section) which satisfies the imposed design constraints. Assuming that there exist optimum section near the one initially selected by continuous optimization, a direct search is conducted to find the discrete optimum solution. The optimization of the entire structure is accomplished through the individual member optimization.
Comparison of the transverse sections of R/C box-girder bridges in Korea with those in foreign countries and parameter studies based on the introduced design algorithm give the following results: (1) cross-sectional area of R/C box-girder bridges in Korea may be reduced to over 15% in an aspect of transverse member forces to maintain the minimum safety margin; (2) the design of R/C box-girder section is dominantly governed by the local constraints related to the longitudinal bending and shear design.
