Fatigue of profiled prestressed concrete beams with web reinforcement under shear load

带腹筋预应力混凝土梁的抗剪强度可以用混凝土贡献和桁架贡献来描述。在循环荷载作用下，它们的抗剪承载性能至今尚未解决。由于混凝土贡献和桁架贡献的比例随着腹板钢筋量的增加而变化，因此这尤其涉及具有中等和较高抗剪钢筋比的构件的疲劳性能。此外，缺乏对开裂（弯剪裂缝、斜拉裂缝）对受剪构件影响的系统研究。由于在循环荷载作用下不同受剪构件之间的力的恶化和各自的重新分布至今没有量化，因此不能修改用于剪切的常用方法的参数以获得安全和经济的结果。此外，常见的方法不考虑在由申请人进行的测试中观察到的循环加载期间的负载水平的影响。计划的研究项目的总体目标是描述在循环加载下由于腹板钢筋的疲劳断裂而失效的异型预应力混凝土梁的承载性能。在这种情况下，不同的剪切承载组件之间的剪切力的分布和它们的演变与负载循环次数的增加是特别感兴趣的。为了回答这些问题，本文对24根中、高配筋率预应力混凝土梁（工字形和T形）进行了试验研究和数值模拟。数值模拟将与非线性有限元程序Abaqus使用自实现的微平面模型与各向异性损伤。它们允许静态剪切强度的常用方法的评估和裂纹状态下疲劳载荷下的应力分析。在研究方案中，应调查剪切开裂类型、抗剪配筋率、预应力、最大荷载和荷载振幅的影响。基于这些结果的方法剪切疲劳参考静态剪切强度的常见模型将导出，占不同的剪切承载组件的恶化。

The shear strength of prestressed concrete beams with web reinforcement can be described by a concrete contribution and a truss contribution. Under cyclic loading their shear bearing behaviour is unresolved so far. This concerns especially the fatigue behaviour of members with medium and higher shear reinforcement ratios, since the ratio of concrete contribution and truss contribution changes with increasing amount of web reinforcement. Furthermore, a systematic investigation on the influence of cracking (flexural shear crack, diagonal tension crack) on the shear carrying components is missing. Since the deterioration and respective redistribution of forces between the different shear carrying components under cyclic loading are not quantified so far, the parameters of the common approaches for shear cannot be modified in order to obtain both safe and economic results. In addition, the common approaches do not consider the influence of the load level during cyclic loading observed in tests carried out by the applicant.The overall objective of the planned research project is to describe the load bearing behaviour of profiled prestressed concrete beams failing due fatigue fracture of the web reinforcement under cyclic loads. In this context, the distribution of shear forces between the different shear carrying components and their evolution with increasing number of load cycles are of special interest. In order to answer the open questions, experimental investigations on 24 prestressed concrete beams (I- and T-shaped) with medium and higher shear reinforcement ratios as well as numerical simulations are going to be carried out. The numerical simulations will be performed with the non-linear FE-programme Abaqus using the self-implemented microplane-model with anisotropic damage. They allow for the evaluation of the common approaches for static shear strength and the analysis of stresses under fatigue loads in the cracked state. Within the research programme, the influence of the type of shear cracking, shear reinforcement ratio, prestressing, maximum load and load amplitude should be investigated. Based on these results an approach for shear fatigue referring to the common models for static shear strength will be derived, accounting for the deterioration of the different shear carrying components.