Optimization of 25-bar truss structure with the consideration of thermal expansion

Abstract

This paper presents the change in the optimal cross-sectional areas of 25-bar truss structure due to thermal expansion. The 25-bar spatial truss is commonly used in structural engineering as a benchmark for structural optimization. Previous studies used different optimization methods to compute the optimal cross-sectional areas of the truss structures related to the minimal weight of each bar element. However, most of the previous studies conducted the optimization under mechanical load only and reported almost the same optimal areas and minimum weight with slight variations depending on the method used. However, very little has been done on the structural optimization with the consideration of thermal expansion. This study aimed to investigate the effect of thermal expansion in structural optimization and conducted optimization of this structure under the thermal load and the same mechanical load case with the previous studies. The difference in the optimal areas between with and without thermal expansion is analysed through optimization of both cases using MATLAB Optimization Toolbox. The optimization method used is fmincon with Sequential Quadratic Programming (SQP) . The result shows both an increase and decrease in optimal cross-sectional areas. The optimal weight of the structure increases by 12.26% at the surrounding temperature of 30°C. Therefore, this study highlights the needs of consideration of thermal load in optimizing the cross-sectional areas of the structure for minimum weight and this is particularly of important consideration in designing the truss structures in tropical climate. One of the limitations of this study that the SQP may not be appropriate for large structure and hence the robustness of the method should be tested with more variable.