可控制精度的预应力混凝土杆系结构时变效应通用分析法

基于杆系有限单元法和时变效应分析的全量形式自动递进法,提出了可控制精度的预应力混凝土杆系结构时变效应通用分析法。有限元法仅用来计算结构的弹性响应,列式中不考虑与时间有关的影响因素;自动递进法仅完成结构不考虑约束情形下的收缩、徐变效应;通过控制有限元法和自动递进法各自计算精度来方便地控制通用分析法的计算精度。建立了考虑混凝土、普通钢筋和预应力钢筋影响的组合单元,单元刚度随混凝土弹性模量时变和预应力钢筋的不断张拉而调整;结合计算锚固瞬间考虑反摩阻影响的预应力钢筋中应力分布的统一算法,建立了可方便计算每束力筋对结构弹性响应贡献的有限元列式,为较准确分析结构时变效应提供了基础。讨论并比较了通用分析法和目前常用分析法的理论计算值及试验结果,表明通用分析法计算精度可控,直到获得满意的精度。

THE PRECISION-CONTROLLABLE GENERAL APPROACH TO ANALYZE TIME-DEPENDENT EFFECT IN PRESTRESSED CONCRETE STRUCTURES

A precision-controllable general approach (PCGA) to analyze time-dependent effect in prestressed concrete structures is presented by using finite element method (FEM) and automatically step-up method (ASUM). In this approach the FEM is only used to calculate elastic responses in which the time-related influences are not considered, while the ASUM is only used to calculate time-dependent effect due to creep and shrinkage for structures under free-constraint, thus the control of computation precision for general approach is fulfilled through precision control of FEM and ASUM, respectively. In this paper a novel built-up beam element including the effect of concrete, prestressed steels and non-prestressed steels is established, and its stiffness is adjusted by the time-dependent modulus of concrete and incessantly tensioned steels. By adopting the unified method to calculate stress distribution along prestressed steels just after anchorage is set up, the general approach can easily calculate the structural elastic response caused by each tendon, which is the base to analyze precisely the time-dependent effects in prestressed concrete structures. The discussion on theoretical values given by PCGA and current frequently used methods and tested data shows that PCGA can achieve agreeable precision.