| The combined structures which are made of bar, beam, membrane, plate and shell elements are used broadly in engineering. Though analyzing the structures with finite element software developed quickly, optimizing the structures in their sections developed more slowly. For that, in this paper the theory about section area optimization of combined structures is researched, and the sectional area optimization program is coded by PCL (Patran Command Language) based on the optimization theory. The main contents researched in the paper are as follows.1. Sectional Optimization Modeling of Combined Structures With the structure weight as the object, the sectional area optimization model of combined structures is built with strength constraints and size constraints. To avoid the heavy computations from the first-order approximation, the strength constraints as local constraints are approached in term of the zero-order approximation to transform to size limits.2. Dimensionless Design Variables To suit the connection of the variables in the engineering reality, the dimensionless design variables are adopted in the paper. Its benefit is that different structural sizes can be controlled by single design variable, such as the thickness of plate element and the area of bar element can be controlled by single dimensionless design variable.3. Approximate Scaling Step Technique Approximate scaling step is a technique to move the design point from the outer or the inner of feasible region to the boundary through multiplying all design variables by a scaling step factor, which is computed with the relations between the structural responses and constraints. The technique can decrease the computations and smooth the iterative process effectively.4. Software Development Based on the upper optimization model and method to constraints, the sectional area optimization software is developed on MSC.Patran&Nastran software. The software can work effectively.
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