基于组合单元的混凝土结构徐变分析方法

CREEP ANALYSIS METHOD OF CONCRETE STRUCTURES BASED ON COMPOSITE ELEMENTS

对混凝土徐变的研究现状和数值计算方法做出评价,提出了混凝土结构徐变计算的空间有限元分析方法。以组合单元为基础,建立混凝土徐变的三维计算模型:将结构的变形、内力状态、结构形式及约束情况均沿时间轴进行划分,再根据结构在每个时间点上各参数的变化值,推导出了混凝土徐变计算的递推公式;又基于虚功原理建立混凝土徐变刚度矩阵,绕过应力与应变,直接通过位移增量计算自由徐变应变增量的等效荷载,提高了徐变数值计算精度;组合单元是对原有实体等参元的继承和拓展,能够分别考虑钢筋和混凝土各自对单元刚度矩阵的贡献,而两者又通过自由度变换的方法有机的结合在一起,构成一种可专门用于模拟钢筋混凝土结构的单元形式。实例分析结果表明:用组合单元做混凝土徐变分析,能够计入钢筋对徐变的阻碍作用,解决在钢筋和混凝土之间的应力重分布问题,更准确的计算出结构变形和内力变化。

This paper evaluates the numerical calculation of concrete creep and proposes a calculation method for creep analysis of concrete structures. Based on the composite element, 3D model of concrete creep is created firstly. Then, according to the time-dependent variation of structural characteristics, recurrence formula is developed. Based on virtual work principle, concrete creep stiffness matrix is established, and equivalent load of free creep strain is obtained step by step. Generally, the composite element inherits and expands the features of original solid isoparametric elements, and considers contributions of steel and concrete to the element stiffness separately. Analyzing results show that the resistance effects of steel to the creep can be conveniently considered using the composite element, yielding more accurate prediction of the stress redistribution between concrete and steel and the calculation of displacements and internal forces of structures.