In this thesis , the resistance performance of concrete - filled steel tubes under simple load is summed up first . according to the resistance expressions under press and bending , a concise formula of resistance under torsion is deduced on the ground of two former formulae . the format of this formula is of good similarity with that under press and bending 在对比了原有的两种计算方法的基础上，对离心钢管混凝土构件在纯扭转作用下的极限承载力公式，提出了与结果试验更加吻合、形式上更为简洁的抗扭承载力实用计算公式，在形式上与轴压和弯曲承载力公式统一起来。
Based on the summarizations the prevenient research results and taken into account the primary problems in those researches on cft structures , this paper proposes the three - dimensional nonlinear virtual laminated element ( 3d - nvle ) to investigate the loading capacities and time - dependent behaviour of cft specimens . in theoretical investigation of the loading bearing capacities of cft specimens , this paper proposed the three - dimensional stress - strain relationship module of core concrete 本文在总结过去有关研究成果的基础上，针对目前对钢管混凝土结构受力特性研究中所存在的主要问题，提出了三维非线性虚拟层合单元法，并对钢管混凝土构件的极限承载力和徐变规律分别进行了深入研究。
The parameters in the study included the fire duration time , the axial load level , the section type and the strengthen method . the ultimate lateral strength , flexural stiffness , dissipated energy and ductility of the columns were compared and analyzed . ( 2 ) based on the stress - strain relations for steel and concrete after high temperature and the temperature field in the structural member , fiber - based model was developed to calculate the hysteretic moment ( m ) versus curvature ( ) relations and the lateral load ( p ) versus lateral displacement ( ? ) ( 2 )在确定高温后钢材和混凝土在往复荷载作用下的应力-应变关系以及构件截面温度场的基础上,考虑力-温度-时间作用路径,建立了火灾后钢管混凝土压弯构件滞回性能的理论分析模型,对火灾后钢管混凝土构件的弯矩-曲率( m - ) 、荷载-变形( p - )滞回关系曲线进行了分析,计算结果与实验结果总体上吻合较好。
Many factors are considered in the study of the nonlinear buckling bearing capacities of the representative concrete filled circular and square steel tube columns , these factors include the sectional form , the slenderness ratio , the steel ratio , and the eccentricity ratio . the comparison between the test and calculating results shows that they have a good agreement . in theoretical investigation of the time - dependent behaviour of cft specimens , based on the three - dimensional viscoelastic theory , this paper proposed the three - dimensional finite element model of creep of core concrete , in which a linear three parameters visoelastic model was adopted 在对钢管混凝土构件极限承载力的分析计算中，本文提出了核心混凝土的三维非线性应力?应变全量和增量本构关系模型，采用完全的拉格朗日表述来考虑与变形历史有关的大变形问题，并对长细比、含钢率和偏心率在较大范围内变化的方、圆钢管混凝土构件的非线性屈曲承载力分别进行了试验和理论对比分析研究，结果表明二者符合较好。
( 3 ) mechanisms of load versus deformation relationship curves of cfst subjected to compression ( tension ) , bending , torsion , shear and combined loading conditions were analyzed based on the numerical method . the stress distributions in the steel tube and core concrete and the interaction between steel tube and core concrete throughout the loading process were investigated . the influences of loading paths on the behaviour of cfst members were also analyzed ( 3 )采用有限元法对钢管混凝土构件在压(拉) 、弯、扭、剪及其复合受力状态下荷载-变形关系曲线进行了全过程分析,分析了受力过程中钢管和混凝土截面应力分布规律、钢管与核心混凝土之间的相互作用,并分析了加载路径对钢管混凝土构件工作性能的影响,较为深入的揭示了钢管混凝土构件在压(拉) 、弯、扭、剪及其复合受力状态下的工作机理。
