Fatigue crack strengthening in steel structures by adhesively bonded steel patches

Orthotropic deck plates were developed in the 1960s and are a frequently used construction method for steel bridges with large spans. In particular, the early structures of this construction method show increasing damage by fatigue cracks. The reasons for this are, among others, the increased traffic loads but also design deficiencies. Rehabilitation methods such as bolted solutions or crack welding are already in demand. However, these methods weaken the cross-section or have a thermal influence on the base material. Therefore, there is a demand for innovative and flexible strengthening concepts. In the field of adhesive bonding technology, the methods of slack and pre-stressed CFRP have become established as reinforcement (Kasper et al., 2020; Ta<spacing diaeresis>ljsten et al., 2009; Kasper et al., 2020; Do and Lenwari, 2020; Yu and Wu, 2017) [1-5]. Because of the high material costs and the complex structure, especially with pre-stressed CFRP, the application of this reinforcement technology has not yet been established in this fiel. In this case, strengthening procedures with bonded steel patches using structural, cold-curing epoxy resin or polyurethane adhesives are the preferred method for developing solutions in a German research project. This article presents a new alternative for fatigue crack strengthening using bonded steel patches. The effectiveness of the strengthening variants is analysed on various notch details. For this purpose, the boundary conditions in steel construction are presented and considered, thus enabling a suitable adhesive selection. The fatigue tests were determined by analytical and numerical calculations, validated by static small-scale and component tests on different notch details. Cyclic tests on lap shear samples initially form the basis for the adhesive behaviour. The results of the tests on reinforced standard notch details show a longer service life of the reinforced test specimens compared to the reference tests. Still, certain feasibility aspects remain open and are part of an ongoing project. The aims are to improve the design, dimensioning, fabrication and assembly results and validate and prepare them for use on the construction site.