ABSTRACT

This study provided an investigation of strain evolutions in bonded and unbonded prestressed reinforced concrete beams via nonlinear finite element analyses considering concrete plasticity and concrete-damaged plasticity. Usually, non-convergence problems often occurred during analyses of prestressed beams due to drastic increase in contact stresses during stress transferring stages and material softening at large deformations. To avoid this issue, material models with gentle softening behaviors can be used. However, authors introduced a method of employing automatic stabilization using damping factor and viscosity parameters to enhance convergencies. Preciseness of models was then verified by test results of ten beams from referenced researches. Furthermore, strains evolution in concrete, rebars, and tendons was investigated. It is noticed that material inelasticity characteristics make the rate of strain activation unique in defining structural performances of beams under loads. However, this concept is not frequently introduced because measuring the strains in experiments was complicated, while most researchers are only interested in load–deflection relationships and conditions at failure stage. This work demonstrates element strains as functions of deflections to show strains activation mechanisms of structural components. The study offered knowledges which can not only enhance material utilization, but also improve the ductility of prestressed beam designs.

摘要

本研究通过考虑混凝土塑性和混凝土损伤塑性的非线性有限元分析，对粘结和非粘结预应力钢筋混凝土梁的应变演化进行了研究。通常，由于应力传递阶段接触应力的急剧增加和大变形时的材料软化，在预应力梁的分析过程中经常会出现不收敛问题。为了避免这个问题，可以使用具有温和软化行为的材料模型。然而，作者介绍了一种使用阻尼因子和粘度参数来提高收敛性的自动稳定方法。然后通过参考研究的十个光束的测试结果验证模型的准确性。此外，还研究了混凝土、钢筋和肌腱中的应变演变。值得注意的是，材料的非弹性特性使得应变激活率在定义荷载下梁的结构性能时是独一无二的。然而，这个概念并不经常被引入，因为在实验中测量应变很复杂，而大多数研究人员只对载荷-挠度关系和失效阶段的条件感兴趣。这项工作展示了元素应变作为偏转的函数，以显示结构组件的应变激活机制。该研究提供的知识不仅可以提高材料利用率，还可以提高预应力梁设计的延展性。这个概念并不经常被引入，因为在实验中测量应变很复杂，而大多数研究人员只对载荷-挠度关系和失效阶段的条件感兴趣。这项工作展示了元素应变作为偏转的函数，以显示结构组件的应变激活机制。该研究提供的知识不仅可以提高材料利用率，还可以提高预应力梁设计的延展性。这个概念并不经常被引入，因为在实验中测量应变很复杂，而大多数研究人员只对载荷-挠度关系和失效阶段的条件感兴趣。这项工作展示了元素应变作为偏转的函数，以显示结构组件的应变激活机制。该研究提供的知识不仅可以提高材料利用率，还可以提高预应力梁设计的延展性。