Experimental Behaviour of Tensioner for Rigid Hangers of Arch Bridges

In steel tied arch bridges where the hangers are made of rigid bars, the replacement of damaged hangers is rather complex. In fact, while generally the cable hangers are already prepared with anchors at the ends and their replacement traces the initial stages of construction with their prestressing, on the contrary, the rigid bars are welded to the arch and the deck, so their replacement must include the design of a new suspension system that allows the insertion of a pretension where this had never been considered. To check the reliability of this new system, a prototype of tensioner was studied for the case of a steel arch bridge in which the high level of corrosion made it necessary to replace all the original hangers with new ones. This entailed the need to test the tensioner performance with the aim of ensuring the axial force transmission between the two hanger segments without slippage in the threads, as well as to test the correct tension setting before construction and putting into service the hangers to be replaced. For this reason, a predictive experimental campaign was carried out on a prototype by means of tests for the mechanical characterization of the materials used, tensile tests of the system, and tensioning tests under load, measuring the displacements and strains of the system elements. The results of the tests, with slippage in the threads limited to the 2% of total elongation, and the turnaround-stressing curves were useful for the definition of the pieces to be assembled during on-site work and for addressing the operating procedures of the tensioning phases on-site during hanger replacement. Validation with the on-site monitoring of stressing operation was conducted at the end; the monitoring of tension through dynamic tests confirmed the agreement of on-site results with the predictive loading tests of the experimental campaign on the tensioner prototype.