Optimization of Prestressing Force in Short, Medium and High Grade Steel Frames using Genetic Algorithm

In this study, the optimization of prestressed cables in steel structures was evaluated. The type of optimization is considered as locating the position of the cables in the floors. Optimizing structures by considering the existing conditions and constraints or the same constraint functions has always been one of the goals of engineers and designers. So far, a lot of research has been done on optimization and various methods have been proposed to solve it. In general, optimization methods can be divided into three categories: mathematical methods, optimization criteria and meta-exploratory methods. In this research, genetic algorithm, which is one of the meta-heuristic methods, has been used. It is necessary to use the genetic algorithm method to have appropriate objective functions and constraints relative to the design variables. In this research, the weight or area of the structure as the objective function and the stress and deformation constraints at the same time are considered as constraints of the optimization problem. The optimal location, diameter and amount of prestressing force of the cables are considered as problem variables. OpenSees software and nonlinear static method were used to analyze the structures. To implement this issue, three- eight- and twelve-story structures with different span ratios in two modes of cross-bracing on top of each other as well as cross-bracing in different spans are examined and it is observed that in 60% of the models two The middle spans and only 40% of the two side spans are braced as the optimal spans, it is also observed that the coefficient of behavior for 3-story structures with one bracing span in the range of 4.61 to 5.88, in 8-story structures and 12-story with two bracing openings varied in the range of 3.51 to 4.9 and 4.04 to 5.34 respectively. It can also be said that the prestressing force for 3-story structures in the range of 0.12 to 0.18, for 8-storey structures in the range of 0.1 to 0.28 and in 12-storey structures in the range of 0.1 to 0.32 the final cable tension varied.