Study On Optimization Design Of Frame-core Tube Structures In Assembled Buildings

Prefabricated buildings have advantages of both industrialized buildings and green buildings and building prefabrication is an important way to achieve transformation of modern construction industry.This paper aimed to study the optimization of the elements and the structure of frame-core tube structure including precast steel-concrete composite structure and precast concrete structure by means of combining optimization theories and finite element software.The main contents and achievements were as follows:1.Sequential Linear Programming(SLP)algorithm based on partial evaluation of the constraint set is presented by introducing selective evaluation strategy.Major and minor constrained conditions are distinguished so as to modify traditional optimization mathematical model.According to the improved SLP algorithm,new mathematical model and the solving procedure are presented.In addition,move limits definition criteria are considered in SLP algorithm to avoid convergence to an unfeasible optimum or objective function oscillations.Numerical examples are analyzed to verify the efficiency and feasibility of the proposed optimization strategy.2.The optimization model of floor system in frame-core tube structure is established.The floor system includes the combination of composite slabs,truss deck plates and steel beams as well as the combination of laminated slabs and superposed beams.Construction cost is taken as the objective function and layout of secondary beams,sections of beams and slabs are set as optimization variables.Based on reduction methods such as model simplification and constraint modification,the equivalent model of floor system in frame-core tube structure is presented.According to continuum model,mechanical analysis of ribbed floor system is presented.The influence of parameters such as the size of steel beam and the position of plastic neutral axis to the mechanical properties of composite beam is analyzed by examples.3.The optimization model of columns in frame-core tube structure is established.The types of column components include steel column,concrete-filled steel tube column and prefabricated column.By the way of theoretical derivation and example verification,the optimal cross section shapes of each column type are obtained.The notion of type coefficient is proposed to merge steel column and concrete-filled steel tube column into unified column,whose optimization model is established.Based on Hamiton's principle,the influence of parameters in shear walls on structural stiffness is analyzed.4.The integrated optimization model of frame-core tube structure is established,which includes precast steel-concrete composite structure and precast concrete structure.By Adopting some reduction methods such as standard layer division and component mergence,the model is simplified to decrease the number of optimization variables and constrained conditions.Global displacement formula of two structure types are obtained in explicit forms based on the principle of virtual work and numerical example is analyzed to verify the correctness of displacement calculation.Furthermore,mechanical properties of bearing members are presented.Global displacement constraint is served as the medium to optimize all components like beam,column and wall.The integrated optimization of frame-core tube structure is realized by global displacement constraints and constrained conditions of different components.5.The optimization program of frame-core tube structure in prefabricated high-rise building is coded.The program uses VB programming language and it consists of four parts including pre-processing stage,internal force acquirement stage,optimization stage and model modification stage.The program can import the data file from Etabs for modelling.The operation of program is simple only to input some parameters in the program interface,then all optimization process is finished automatically.In addition,four examples are analyzed and compared to verify the accuracy and effectiveness of the program.Examples contain the comparison of standard optimization mode and regular optimization mode,efficiency of improved SLP algorithm and optimization effects of 24 story and 27 story high-rise buildings.The program can satisfy all design requirements of standard and serve as an effective tool to designers in the preliminary design stage.6.The relationship between prefabrication ratio and construction cost is analyzed in frame-core tube structure.From two aspects of single building and main structure,standards for assessment of prefabricated building are compared in the whole nation and in Shanghai to increase the practicability of the paper.