Abstract
A general approach to the multiobjective reliability-based optimum (MORBO) designs of prestressed concrete beams (PCB) is presented in this paper. The proposed approach incorporates all behavior and side constraints specified by the American Concrete Institute (ACI) code for prestressed concrete. Loading, material properties, prestressing force and the models used to predict structural performance at various stages—initial, final and ultimate—are all treated as random variables. A general MORBO methodology is solved by integrating PCB design and reliability analysis computer programs with an automated design optimization package. Only bi- and tri- multiobjective (MO) formulations, subjected to eleven reliability constraints and four geometrical constraints, are considered. The competing objectives in the multiobjective optimization of PCB are selected from, minimization of the overall cost of the PCB, maximization of the system reliability index, maximization of the flexural strength reliability index, and maximization of the tensile stress reliability index at service stage. The design variables consist of six geometrical dimensions that shape the PCB cross section and one that represents the amount of prestressing steel. Numerical examples illustrate the application of the proposed approach to the MORBO of PCB are presented. The ε-constraint (trade-off) approach is used for the solution of the MORBO.