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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。
The research status and numerical calculation method of concrete creep are evaluated, and the space finite element analysis method of creep calculation of concrete structure is proposed. Based on the combination unit, the three-dimensional model of concrete creep is established. The deformation, internal forces, structure and constraints of the structure are all divided along the time axis. Based on the change of each parameter of the structure at each time, Based on the principle of virtual work, the creep stiffness matrix of concrete is established, and the equivalent load of free creep strain increment is directly calculated by displacement increment by bypassing the stress and strain. The combination unit is the inheritance and expansion of the isoparametric elements of the original entity, which can separately consider the respective contribution of the reinforcement and the concrete to the element stiffness matrix, and the two are organically combined by the method of freedom degree transformation, Constitute a unit that can be used exclusively to simulate reinforced concrete structures. The case study shows that the creep analysis of concrete with composite elements can account for the impeding effect of reinforcing steel on creep, solve the problem of stress redistribution between reinforcing bars and concrete, and calculate the structural deformation and internal force more accurately.