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复合桥梁中，混凝土和钢结构建筑构件之间的纵向剪切传递是由头钉保证的。这些结构不仅在主承重方向上受到疲劳，就像过去的情况一样，而且在横向上也受到疲劳。在公路桥梁中，尽管公路桥梁的应力范围往往不是很高，但其横向承载的结构构件的荷载循环次数却高达数亿次。因此，必须对以下两个问题进行基本的科学处理：-对迄今为止完全未开发的带有头螺栓的疲劳应力剪切连接器的耐久性极限进行理论和实验证明，包括设计所需的安全裕度；-对头螺栓在多轴疲劳载荷下的应力条件进行分析，并对设计结果进行分析。由于国际上很少有关于螺栓在剪切载荷下的疲劳极限的实验结果，因此这种多达3000万次载荷循环的疲劳试验是强制性的。由于大量的负载循环和由此产生的测试工作，统计有效结果所需的测试程序只能在两所大学中合理地实现。为了避免目前常用的推出式试验的缺点，设计了一种新型的并联试验平台，该平台可以对销钉组进行多轴疲劳加载。此外，pat - tfm，一种新的土木工程无损检测方法，将进一步发展，这样可以在早期阶段检测到头螺柱焊接接箍产生的裂纹，并根据裂纹起裂和裂纹扩展阶段的划分进行理论评估，这将与之前已知的低应力范围研究有很大不同。这些试验是由数值调查补充的，数值调查基于先前的调查，特别关注路桥的典型低荷载水平。特别要注意的是在这种荷载水平下混凝土上的局部应力，以及它们对铆钉焊接接箍内外边缘应力峰值的影响。考虑输入参数的分布，采用概率疲劳分析来确定设计所需的安全裕度，即疲劳极限的设计值。为了完成该项目，将使用目前设计的三座大型桥梁，通过计算和测量来验证螺栓的整体和局部疲劳应力与合理的疲劳极限设计值的水平。

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.