Application of a Toughened Epoxy Adhesive for the Fatigue Strengthening of Steel Structures

Many steel bridges in different countries are reaching their design life­time or they present structural deficiencies due to the increase of traffic loading or deterioration. In Europe, more than half of steel bridges need to be upgraded since they are more than 50 years old. Fatigue-related issues are often present due to lack of maintenance or inspection. Among the different approaches to extend the fatigue lifetime, the local strengthening is a valid and cost-effective alternative to the whole replacement of damaged parts. The use of bonded steel plates instead of traditional joining techniques, such as welds or bolts, avoid the presence of new stress raisers. Finally, the adoption of bonded composite plates instead of traditional steel plates results in a strengthening solution easy to handle and to install, less sensitive to corro­sion and with a limited increase of the dead load. Recently, a two-component epoxy adhesive with outstanding mechanical properties, such as a very high toughness, was proposed (Meier T et al. in IABSE congress Christchurch 2020: resilient technologies for sustainable infrastructure - proceedings, pp 898-902, 2020) for the strengthening of fatigue sensitive structural steel elements. In Kasper et al. (Constr Build Mater 275, 2021), fatigue crack propagation at both the steel-reinforcement interface and in the steel substrate were studied. In particular, fatigue crack propagation at the interface was investigated by using an empirical approach (S-N curves). In this paper, starting from single-lap direct shear fatigue tests, the calibration of a feasible cohesive model for fatigue crack propagation at the interface is performed. To this end, a model recently proposed in the literature for the interface modeling under general cyclic loading conditions is adopted. The identified model parameters are then used to simulate the interface fatigue crack propagation, showing a good comparison between numerical and experimental results.