Analysis of a bolted T-stub strengthened by backing-plates with regard to Eurocode 3

The connection reinforcement by backing-plates, which is of low cost and simple to realize, can give performances which get closer to that of stiffeners in the tension zone. Currently, in the Eurocode 3, this reinforcement mode is considered only for resistance. The T-stub, a main component in the bolted connections under bending, is analysed at first in the non-reinforced stage as a calibration of the finite elements modelling approach. Then, the T-stub is reinforced by backing-plates with various geometrical configurations. The aim is to better understand the behaviour and the mechanical contribution of backing-plates considering the stiffness and the resistance. The 3D model developed in the finite elements software Cast3m takes into account elastic plastic behaviour of the materials, the large displacement and the unilateral contact between the connected parts. This model shows a good capacity to represent the available experimental results. The sensitivity analysis of T-stubs reinforced by backing-plates to various parameters such as the thickness of the backing-plate and the pre-tension force allows us to show that the contribution of the backing-plate in term of stiffness is significant in some cases and in particular with preloaded bolts. The T-stub behaviour is analysed on the basis of the global load–displacement curves, the evolution of the bolt load and the contact pressure due to the prying force effect. The analysis shows that the resistance of the T-stub increases in a significant way with the thickness of backing-plate. This increase has an upper limit due to the failure mode change which occurs for lower values of loads according to the analytical model, which gives a reserve of resistance for the reinforced T-stub.