Advanced Analysis And Its Layout Optimization Design Of Latticed Steel Frame Based On Second-order Elastoplastic Theory

The structural analysis and optimization are the two key points of structural research.In the application of engineering structure,the enterprise and researcher demand the theory and method of structural analysis can describe the real displacement reaction path under the loading,which is the demand for structural safety.On the other hand,they hope the structural optimization methods can include more design parameters and acquire more economic interest,which is the demand for lightweight.For the study of discrete steel frames,the structural analysis went through the periods of linear elastic analysis,first-order elastoplastic analysis,second-order elastic analysis,second-order elastoplastic analysis and advanced analysis.Advanced analysis had reached the goal to reflect the real relationships between loads and displacements.Meanwhile,the structural optimization experienced the stage of shape optimization,size optimization,topology optimization and layout optimization.The layout optimization design can nearly consider all the structural design parameters.The advanced analysis and high-level layout optimization means are steel the research hotpots,but a relatively rich knowledge system has formed in their respective fields.This dissertation combines the advanced analysis that can reflect the real carrying capacity of the steel structure with the high-level layout optimization method to form the new layout optimization idea based on the advanced analysis of the latticed steel structure.Firstly,the whole process of advanced analysis was realized and optimized from three aspects:stiffness expression of second-order beam-column element,transformation of nonlinear coordinate matrix and nonlinear numerical solution.The key research issues are the stiffness expression of second-order beam-column element,the defective element expression of component and the numerical solution algorithm.Secondly,the ultimate bearing capacity and ultimate displacement of the output results of advanced analysis are taken as constraints to realize the real layout optimization of steel frame structures.Finally,the engineering experiment combined with FEM simulation software ABAQUS was designed to validate the accuracy of advanced analysis results.The main contributions of this thesis are listed below:(1)The advanced analysis procedure of steel structure was written by independent programming method.The total technologic process of advanced analysis of steel frame was expounded and optimized in three aspects as the rigidity expression technology of second-order beam-column element,the translational technology of nonlinear coordination matrix and the numerical technology of nonlinear solutions.The precise of transverse displacement filed and twisting displacement expressed by second-order beam-column element and cubic Hermite interpolation of finite beam element was compared.Rigidity of second-order beam-column element with initial twisting imperfection were derived,and single sine wave imperfection from steel design code were expanded to double sine wave according to engineering practice and steel code in domestic and overseas.All of the above promotions contribute to more general application of advanced analysis method based on second-order elastoplastic theory.(2)Five imperfect models from the universe three-leg latticed beams and four-leg latticed columns were designed to validate the accuracy of analytical method.The models were conducted with advanced analysis using the nonlinear numerical iteration procedure of Newton-Raphson load increment iteration method and Risk arc length control method,respectively.And software ABAQUS with nonlinear post-buckling analysis with imperfect model was used to validate the precise of advanced analysis of latticed steel frame based on second-order elastoplastic theory.(3)For the layout optimization of discrete structure with bars system,the numerical model issue of layout optimization that some researchers regard the steel frames as truss structures was summarized in the article.According to the idea of modern steel design code,a general layout optimization model was built,that react the real ability of spaced steel frames.The complexity of the numerical model based on steel structure design code was presented.At last,setting the output results of critical carry load and critical displacement required by advanced analysis as the constraint conditions of layout optimizing model,a new numerical model of layout optimization was created,which express a new layout optimization idea based on the advanced analysis based on second-order elastoplastic theory.(4)In the process of layout optimization based advanced analysis,a two-way control method of reliable topology and guided genetic algorithm(KLGA)was proposed based on the improvement of the genetic algorithm(GA),which aims to search the best solution in the complex solution space of layout variable.In one respect,this method enables the separation of the topological variables from the layout design variables,and then integrates them after evaluating the reliable topological variable combinations based on component importance.In addition,the guidance information of structure was added in the algorithm to guide the path of global optimal solution for GA.(5)Eight pieces of four-leg latticed test columns were divided to three groups to conduct the experimental testing,which aim to detailly study the influence of cross-section type of lacing bars,layout type of lacing bars and the eccentricity of compressive load on the critical carry load,respectively.Prior to the loading test,the initial bending and twisting imperfections of legs and latticed bars were measured in the installation state.Through the statistics and analysis of the engineering test imperfect dates,the general applications of rigidity expression of second-order beam-column element with imperfection were proved.In the loading test of the relationship of load and displacement reactions in test points,the experimental test was combined with the nonlinear post-buckling analysis with imperfect model by ABAQUS,which jointly validate the accuracy the advanced analysis method based on second-order elastoplastic theory.Above all,the systematical analysis were developed for the advanced analysis and its layout optimization design of latticed steel frame based on second-order elastoplastic theory,including diversity analytical means of theoretical analysis,autonomous programming design,FEA simulation and experimental testing.The researches enrich the technical system of advanced analysis of steel structure and construct the new layout optimization idea based on advanced analysis,which have an important significance for layout optimization design of spaced latticed steel structure.