Reliability based constant amplitude fatigue limit of shear connection with headed studs for single or multi-axis fatigue loading

在未来几十年计划建造的许多新的大型组合桥梁中，混凝土和钢建筑构件之间的纵向剪切传递是通过大头钉来确保的。这些不仅在主承载方向上经受疲劳，就像过去的情况一样，而且在横向方向上也经受疲劳。在公路桥梁中，结构构件在横向方向上承受的载荷循环次数高达数亿次，尽管公路桥梁的应力范围通常不是很高。因此，必须对以下两个问题进行基本的科学处理： 带大头钉的疲劳应力剪力连接件的疲劳极限迄今完全未探索的理论和实验证明，包括设计所需的安全裕度， 分析了有头螺栓在多轴疲劳载荷下的应力状况及其设计结果。由于国际上对于有头螺柱在剪切载荷下的疲劳极限的实验结果很少，因此必须进行高达3000万次载荷循环的疲劳试验。由于大量的负载循环和由此产生的测试工作，统计上有效的结果所需的测试程序只能在两所大学合理地实施。为了避免目前常用的推出试验的缺点，设计了一种新型的试验台，并进行了并行试验，它也允许多轴疲劳加载的传力杆组。此外，PAUT-TFM，一种新的方法，在土木工程中的无损检测，将进一步发展的方式，起源于焊接环的头螺栓的裂纹可以在早期阶段检测和理论上评估有关的裂纹萌生和裂纹扩展阶段，这将是非常不同的比以前已知的低应力范围在这里调查。测试是补充的数值研究，其中，根据以前的调查，特别侧重于低负荷水平的典型公路桥梁。特别要注意的是，在此荷载水平下发生在混凝土上的局部应力及其对应力峰值的影响，发生在螺栓焊接环的外部和内部边缘。概率疲劳分析用于证明所需的安全裕度在设计中，即疲劳极限的设计值，考虑到输入参数的分布。为了完成该项目，将使用三座现行设计的大型桥梁，通过计算和测量来验证有头螺栓的整体和局部疲劳应力与疲劳极限的合理设计值相比处于何种水平。

In the construction of many of the new large composite bridges planned for the coming decades, the longitudinal shear transfer between concrete and steel building components is ensured by headed studs. These are subjected to fatigue not only in the main load-bearing direction, as was the case in the past, but also in the transverse direction. In highway bridges, the number of load cycles for the structural members bearing in the transverse direction is many hundreds of millions, even though the stress ranges for highway bridges often are not very high. Thus, a fundamental scientific treatment of the following two issues is imperative:- Theoretical and experimental justification of a hitherto completely unexplored endurance limit for fatigue-stressed shear connectors with headed studs, including the required safety margin for design, - Analysis of the stress conditions under multiaxial fatigue loading for the headed studs and consequences for design. Since few experimental results exist internationally for the fatigue limit under shear loading of headed studs, such fatigue tests with up to 30 million load cycles are mandatory. Because of the high number of load cycles and the resulting test effort, the test program required for statistically valid results can only be reasonably implemented at two universities. In order to avoid the disadvantages of the push-out tests commonly used so far, a novel test rig is designed and tested in parallel, which also allows multiaxial fatigue loading for dowel groups. Furthermore, PAUT-TFM, a new method for non-destructive testing in civil engineering, will be further developed in such a way that the cracks originating from the weld collar of the headed studs can be detected at an early stage and theoretically evaluated with regard to the delimitation of crack initiation and crack growth phases, which will be quite different than previously known for the low stress ranges investigated here. The tests are supplemented by numerical investigations, which, based on previous investigations, focus in particular on the low load level typical of road bridges. Particular attention is paid to the local stresses on the concrete that occur at this load level and their effects on the stress peaks occurring on the outer and inner edge of the weld collar of the studs.Probabilistic fatigue analysis is used to justify the required safety margin in design, i.e. the design value of the fatigue limit, taking into account the distributions of the input parameters. To round off the project, three large bridges of current design will be used to verify by calculation and measurement at what level the global and local fatigue stresses of the headed studs lie in comparison to the justified design value of the fatigue limit.