Design of Prestressed Concrete Girder Bridges Using Optimization Techniques

摘要

A comprehensive study for deterministic design of simply supported pre stressed concrete girder bridge is presented. Using the feasible direction method, a set of optimal geometrical dimensions, girders spacing, amount of prestressing steel, prestressing loses and tendon profile are obtained. The constraints that have been used are based upon flexural stress at initial and final stages, crack width, initial camber, deflection due to both dead and live loads, total loses, ultimate moment capacity with respect to the factored loads and cracking moment and the ultimate shear strength. This aims at finding the optimum design of pre stressed concrete girder bridge system and finding the most economical tendon profile out of three profiles, namely parabolic, L/3 harped, and triangular tendon profiles. The problem is formulated in general form so that introduction of specific regulations following from national codes is possible. The computer programs for optimal design of pre stressed girders bridges is developed. The numerical examples are computed taking into account the rules of AASHTO or ACI design codes. Numerical examples of pre stressed concrete girder bridges with standard and general sections are solved to show the efficiency of the above formulation. The results indicate that the parabolic tendon is the optimum one, especially for long spans. Also, the cost is slightly nonlinear function of span length. Therefore it can be reasonably approximated as a liner relationship. There are more savings on the cost when the section is allowed to crack. Stress at jacking end controlled the optimum design for long spans, while the shear strength requirement controlled the design for short spans.