An experimental campaign for assessing the role of tensioned tendons on the shear capacity of half-joints

An important percentage of bridges and viaducts constituting the Italian road infrastructures dates back to the years 50s and 60s and is characterized by prestressed r.c. decks adopting half-joints for obtaining statically determinate schemes. In existing bridges, half-joints are often subjected to degradation phenomena, mostly promoted by water percolation and stagnation, which led to classify the bridge in a high attention class, according to the Italian Guidelines for Risk Classification and Management, Safety Assessment and Monitoring of Existing Bridges. Furthermore, half-joints are difficult to inspect and to maintain. The current safety assessment procedures at ultimate limit state are based on simplified Strut&Tie models that usually neglect the contribution of prestressing tendons anchored in the half-joints on the resisting mechanisms and the ultimate capacity. This work presents the design of an experimental campaign for investigating the shear behaviour and the ultimate capacity of half-joints in which inclined prestressed tendons are anchored. In detail, six laboratory scaled post-tensioned beams are built with half-joints in correspondence of the support regions, dimensioned on the basis of a real bridge girder and numerical 3D finite element nonlinear analyses. The main research goal is to evaluate the influence of tendons on the half-joints capacity by comparing results with those obtained from specimens with non-tensioned tendons and without tendons. Three levels of pre-tensions in specimens characterized by the same reinforcements are considered. In addition, for one level of pre-tension, the effects of different half-joints detailing are investigated. Finally, the role of degradation due to ageing is also addressed by inducing corrosion in one specimen through a galvanic method.