Study On Robust Optimization Design Method Of The Cantilever Structures

With the development of the economic science and technology, the civil engineeringstructures became more and more complex and diversiform, in which the cantileverstructures like tower structure are widely applied and developed. Higher requirement tothe structural optimization design method was put forward consequently. Therefore it is ofgreat practical significance to applied new optimization method to engineering. In thispaper, optimization design method to the cantilever structure was studied both by theoreticmethod and numerical method.Disadvantages and limitations of traditional optimization design and Taguchi robustdesign method to the cantilever structure were analysed. To make up for each other'sdeficiencies, robust optimization design method was presented, in other words, combiningthe optimization design and robust design together. Firstly, optimization solutions ofdesign parameters of cantilever structure were obtained by optimization design method;then, the parameters were redesigned by using Taguchi robust design method, which isonly appropriate for single-objective, less-variable and unconstrained problem. Anumerical example is taken out to prove the method to be effective.In order to consider the effect of the uncertain factor to the behaviour of cantileverstructures, reliability analysis was introduced. Structural reliability undermulti-failure-mode was studied. If the limiting status function was explicit function,random perturbation theory was applied to determine first four moments and dependenceof the different failure-modes. Four moments technology was applied to determine thereliability index, and gradient algorithm was applied to determine the sensitivity of therandom parameters. The effects of the random parameters to the structural reliability wereconsidered also.If the limiting status function was implicitfunction, the modified response surfacemethod was applied to analyse the structural reliability. Importance sampling method wasintroduced to compute the structual failure probability. The modified First-order-second-moment method was applied to compute the sensitivity of failure probability to the random variable.In order to consider the effects of uncertainty and random fluctuation to structuralbehaviour, the optimization design and robust design were combinned together.Mathematical models of reliability robust optimization design for the cantilever structurewere established. Reliability sensitivity was introduced to the objective function.Therefore, reliability robust design was boiled down to the multi-target optimizationproblem which satisfied the reliability requirement.In order to solve the mathematical models of reliability robust optimization design,comparative analysis to the multi-target optimization algorithm was presented. Themodified non-inferiority delamination genetic algorithm was put forward.The reliability robust optimization design method was applied to the optimizationdesign of a communication tower in Shanghai. By compaired with the traditionaloptimization design result, practical applicability and effectiveness were presented.