Retrofitting of a Steel Truss Joint by Creating Composite Connections and PTMSs (Post-Tensioned Metal Straps)

The fatigue phenomenon has a significant effect on the joints of steel truss bridges, causing the formation of plastic hinges leading to potential collapse configurations. For this reason, in the last few years, the development of new methods to effectively strengthen such joints has gained attention. In this article, a mechanism for the improvement of the resistance to fatigue of these types of connections is proposed, by employing composite joints and post-tensioned metal straps (PTMSs). Following this approach, first the overstressed connections of the structure have been identified during the inspection phase, and subsequently, they have been encased in a concrete casting with a proper level of strength. To analyze the behavior of the steel-concrete mixed solution, a finite element model has been realized in ABAQUS (rel. 2022.0) and it has been validated based on comparison between the numerical results and the experimental ones obtained by laboratory tests. Then, a parametric analysis was performed to investigate the effect of the concrete type employed in the connection behavior. In the second stage of the research, based on the first cracks configuration obtained numerically and observed experimentally, PTMSs have been used to control the cracks and strengthen the joint. The strains and stresses on the concrete and steel parts of the connection were measured before and after the insertion of the PTMSs and compared with the outputs of the model. Additionally, a parametric analysis was carried out to assess the optimal number of straps. The effect of this solution on the resistance of the joint and on the behavior of concrete was analyzed and the effectiveness of the strengthening technique was assessed.