Both the entire weight and joint displacements of grid structures are minimized at the same time in this study. Four multiobjective optimization algorithms, NSGAII, SPEAII, PESAII, and AbYSS are employed to perform computational procedures related to optimization processes. The design constraints related to serviceability and ultimate strength of grid structure are implemented from Load and Resistance Factor Design-American Institute of Steel Constructions (LRFD-AISC Ver.13). Hence, while the computational performances of these four optimization algorithms are compared using different combinations of optimizer-related parameters, the various strengths of grid members are also evaluated. For this purpose, multiobjective optimization algorithms (MOAs) employed are applied to the design optimization of three application examples and achieved to generate various optimal designations using different combinations of optimizer-related parameters. According to assessment of these optimal designations considering various quality indicators, IGD, HV, and spread, AbYSSS shows a better performance comparatively to the other three proposed MOAs, NSGAII, SPEAII, and PESAII. 1. Introduction The grillage systems utilized in different structures like bridge or ship decks, building floors and space buildings, and so forth, contain traverse and longitudinal beams, which are made of available steel profiles with different cross-sections. The optimal selection of steel cross-sections from a discrete set of practically available steel profiles provides a big contribution to constructing cost of a grid structure. Therefore, either weight of grid structure or deflection of its joints is minimized according to certain design limitations prescribed by any code of practice, such as LRFD. During the design optimization of grillage systems, designer is frequently faced with a problem related to making a decision about determination of the most appropriate one between these two conflicting and commensurable objective functions. Although a displacement-related constraint is imposed as a (max span/300) according to the provisions of LRFD-AISC specification, the safety margin on displacement constraint is large when taking into account the grid structures with higher sensitivity against displacement, such as ship decks and floors of industrial buildings which bears special machines required an horizontally balanced position for a regular work. This task has been easily overcome in a way of introducing the concept of multiobjective optimization to the design applications of grid
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