Fatigue Behaviour of notches and self-drilling fully threaded screws for the application as connection in Timber-Concrete Composite Beams

该项目的主要目的是分析具有缺口连接的木-混凝土组合梁（tcc -梁）在循环荷载下的疲劳行为，并为疲劳验证提供指导。首先，应审查钢结构和钢-混凝土组合结构设计中公认的方法和程序的可移植性。应进行适当的疲劳验证，以便在公路桥梁和其他具有相关疲劳载荷的建筑物中实际应用这种连接。与其他tcc连接类型相比，缺口连接的特点是具有很高的强度和刚度值，并且易于施工。实际应用的第一个例子是存在的，但这些都是试点项目。在木材标准全面实施之前，必须澄清一些悬而未决的问题。例如，一个问题是，最初为钢和钢-混凝土组合梁开发的验证过程（基于s - n曲线和Palmgren和Miner的线性损伤累积假设）是否也适用于缺口连接的木-混凝土组合梁，或者是否需要额外的限制。因此，将进行初步研究，以确定在变幅谱中顺序排列可能产生的影响，以及在进行多次无断裂循环试验后的剩余承载能力。对缺口连接疲劳行为的初步实验研究表明，缺口前的木梁存在脆性剪切破坏机制。为了防止这种脆性破坏机制，将分析全螺纹螺钉加强缺口作为一种创新的解决方案。因此，除了未加固的缺口外，加固的缺口连接与缺口加载边缘前的螺钉将进行疲劳测试。此外，为了提高缺口的强度，第二个目标是研究全螺纹螺钉的疲劳行为。对全螺纹螺钉的疲劳性能进行基本研究，不仅可以用于加强TCC缺口连接，还可以用于其他应用，从而安全有效地使用这种连接。为了实现这一点，对于所有三种类型的载荷：剪切、拉出和相互作用，全螺纹螺钉的疲劳行为应该在部件试验中进行分析，并得出适当的疲劳验证。

The main objective of the project is to analyse the fatigue behaviour of timber-concrete composite beams (TCC-Beams) with notched connections under cyclic loading and provide guidelines for the fatigue verification. Firstly, the transferability of accepted methods and procedures in design of steel and steel-concrete-composite constructions should be reviewed. An appropriate fatigue verification should be derived in order to allow for the practical application of this connection in road bridges and other types of constructions with relevant fatigue loading. Compared to other TCC-connection types the notched connection is characterized by very high strength and stiffness values and its ease of construction. First examples of practical application exist, however these are pilot projects. Before a general implementation in the timber standard, some open questions have to be clarified. One issue e.g. is whether the verification process, originally developed for steel- and steel-concrete-composite beams (on basis of S-N-Curves and the linear damage accumulation hypothesis by Palmgren and Miner), is also applicable for timber-concrete-composite beams with notched connections or whether additional limitations are necessary. Therefore, preliminary studies will be conducted to identify possible effects of sequential arrangements in variable amplitude spectrum and the remaining bearing capacity after a cyclic testing for a number of cycles without fracture.Initial experimental investigations of the fatigue behaviour of notched connections have shown a brittle shear failure mechanism in the timber beam in front of the notch. To prevent this brittle failure mechanism, fully threaded screws reinforcing the notch will be analysed as an innovative solution. So, besides the unreinforced notch, reinforced notched connections with screws in front of the loaded edge of the notch will be tested for fatigue. In addition, to the enhancement of the strength of the notch, the second aim is the investigation of the fatigue behaviour of the fully threaded screws. A basic investigation of the fatigue behaviour of fully threaded screws should enable a safe and efficient use of this connection not only for reinforcing TCC notched connections but for other applications. To achieve this, for all three types of loading: shear, pull-out and interaction the fatigue behaviour of fully threaded screws should be analysed in component tests and an appropriate fatigue verification derived.