基于Kelvin链率型模型的混凝土徐变有限元计算

基于混凝土徐变固结理论,推导出一种计算混凝土徐变的递推格式,递推过程可以结合使用有限元商用软件来完成。首先,基于Kelvin链模型,将徐变Volterra积分方程转化为率型徐变积分微分方程;其次,将时间进行离散,通过引入中间变量,把率型徐变积分微分方程转化为可递推计算徐变方程;再次,使用可递推计算徐变方程,结合应力应变增量弹性本构关系,建立考虑复杂应力状态下混凝土徐变分析的包含初应变的应力应变增量弹性本构关系。在此本构关系基础上,构建初应变弹性结构有限元分析模型;最后,作为应用,对Ansys有限元商用软件进行二次开发,用Fortran语言修改Ansys软件中材料本构子程序Usermat,并用其计算了一些现有算例。计算结果表明,研究结果与现有算例结果吻合优良。研究方法无需记录应力历史,大大提高计算效率,亦为复杂结构混凝土的徐变计算提供了另一条有效途径。

Finite Element Calculation of Concrete Creep Based on Rate -Type Law Visualized by the Kelvin Chain Model

Based on the solidification theory, an recursion format for calculating concrete creep is derived. The recursion process can be programmed by commercial finite element software. Firstly, the creep Volterra integral equation was transformed into a rate-type creep integrodifferential equation based on the Kelvin chain model; secondly, the integrodifferential equation was transformed into a recursive creep calculation equation by discretizing the time and introducing intermediate variables; thirdly, a stress-strain incremental elastic constitutive relationship with initial strain was established by using the recursive calculation. The stress-strain incremental elastic constitutive relationship was suitable for complex stress conditions. Finally, as an application, the Ansys finite element commercial software was re-developed by modifying the material constitutive subroutine Usermat with Fortran language. Some existing examples were calculated by the program. The calculation results show that proposed method has satisfactory accuracy by comparing with the existing results. The proposed method does not need to store the stress history, which greatly improves the calculation efficiency, and also provides another effective way for the creep calculation of complex concrete structure.