High capacity saw tooth connections under cyclic loadsResearch of high-capacity saw-tooth-connections in cyclic loads for the transfer of extremely high and concentrated tangential forces between slender steel and concrete elements

在当前DFG研究项目中，该研究提案的申请人证明，锯齿连接非常适合将非常高且集中的切向力从钢传递到混凝土元件中，例如在桥梁结构中。然而，分析分析和实际测试仅研究静态载荷。相比之下，锯齿连接最重要的应用是在建筑物和结构中，这些建筑物和结构主要承受动态载荷。本研究的目的是对循环荷载作用下的锯齿连接进行初步和基础性的研究。迄今为止进行的理论预分析表明，锯齿连接在循环载荷下将显示出非常高的承载能力。主要原因是大面积的混凝土和钢材，可用于承受压力。因此，混凝土和钢筋中的应力非常低且均匀，没有高的应力峰值。据推测，钢中的应力低于其疲劳抗力。直到今天，还没有关于这个问题的理论或实践的科学研究。申请人对带有倾斜锯齿连接器的混凝土棱柱进行了第一次初步试验。在2 Mio负载循环后，它们显示负载能力没有降低，Pmax/Pu = 0.67，Δ P/Pu = 0.48。然而，在现实中，与棱镜测试相反，沿着锯齿连接器沿着的载荷分布不是恒定的，而是在锯齿连接器的尖端处显示出力的峰值。这就是为什么锯齿连接在更真实的部件测试中的性能到今天还无法预测的原因。此外，连续梁跨中连接可能会受到荷载方向的变化。在本研究提案中，将首次研究改变加载方向的影响。在初步试验中，在混凝土中观察到平行于压杆的小裂纹。在改变加载方向的情况下，这将导致垂直裂纹，压杆穿过裂纹。目前还不清楚这些裂纹如何影响动态载荷下锯齿连接的承载能力。在拟议的研究项目中，将首次对这种影响进行调查。试验期间将使用连续超声波测量，以检测混凝土断裂区域。该研究项目的目的是首次对锯齿连接在脉动和交变载荷下的承载行为的基本原理进行基础研究。重点研究了锯齿连接区交叉裂纹的影响。

In a current DFG research project the applicant of this research proposal demonstrated, that saw-tooth connections are exceptionally well suited to transfer very high and concentrated tangential forces from steel into concrete elements, for example in bridge structures. However, the analytical analyses and practical tests were only investigating static loads. In contrast, the most important applications of saw-tooth connections are in buildings and structures, which are predominantly exposed to dynamic loads. The goal of this research proposal is a first and fundamental investigation of saw tooth connections under cyclic loading. The theoretical pre-analysis, conducted so far, indicates, that saw tooth connections will show a very high load bearing capacity in cyclic loading. The main reasons are the large areas of concrete and steel, which are available for the bearing of the compressive forces. As a result, the stresses in the concrete and the steel are quite low and uniform, without high peaks of stresses. It is supposed, that the stresses in the steel are lower than its fatigue resistance. Until today there is no scientific research, theoretical or practical, available on this subject. The first preliminary tests of concrete prisms with inclined saw tooth connectors, were carried out by the applicant. They showed no reduction in the load capacity after 2 Mio load cycles, with a Pmax/Pu = 0,67 and a deltaP/Pu = 0,48. However, in reality and in contrast to the prism-tests, the load distribution along the saw tooth connector is not constant, but shows a peak of forces at the tip of the saw tooth connector. That is why the performance of saw-tooth connections in a more realistic component test cannot be predicted by today. In addition, the connections in the mid-span of continuous beams may be subjected to changing loading directions. The effect of changing loading directions will be examined, for the first time ever, in this research proposal. In the preliminary tests, small cracks parallel to the compression struts were observed in the concrete. In the case of changing loading directions, this would result in perpendicular cracks, with the compression struts crossing the cracks. It is absolutely not clear, how these cracks will influence the load bearing capacity of saw tooth connections under dynamic loads. For the first time, this effect will be investigated in the proposed research project. A continuous ultrasonic measurement will be used during the tests, to detect the areas of fractured concrete. The aim of this research project is the first fundamental research into the basic principles of the load bearing behavior of saw tooth connections under pulsating and alternating loads. Special emphasis is laid on the research into the effects of crossing cracks in the area of saw tooth connections.