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

腹板配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，其剪切承载性能尚未得到解决。这尤其涉及具有中等和更高剪切配筋率的构件的疲劳行为，因为混凝土贡献和桁架贡献的比例随着腹板配筋量的增加而变化。此外，对裂缝（弯剪裂缝、斜张裂缝）对承载剪力构件的影响还缺乏系统的研究。由于在循环荷载作用下，不同承载构件之间的力的劣化和各自的重分布尚未量化，因此，为了获得既安全又经济的结果，无法对常用剪切方法的参数进行修改。此外，通常的方法没有考虑在申请人进行的试验中观察到的循环加载期间荷载水平的影响。计划研究项目的总体目标是描述在循环荷载下由于腹板钢筋疲劳断裂而失效的预应力混凝土梁的承载行为。在这种情况下，不同承载剪切构件之间的剪切力分布及其随荷载循环次数增加的演变是特别有趣的。为了回答这些悬而未决的问题，将对24根中、高抗剪配筋预应力混凝土梁（I型和t型）进行试验研究和数值模拟。数值模拟将使用非线性有限元程序Abaqus，采用自实现的各向异性损伤微平面模型进行。它们允许评估静态剪切强度的常用方法和裂纹状态下疲劳载荷下的应力分析。在研究方案中，应研究剪切开裂类型、剪切配筋率、预应力、最大荷载和荷载幅值的影响。在此基础上，推导了考虑不同承载构件劣化的静态抗剪强度通用模型的抗剪疲劳计算方法。

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.