Stressing Sequence for Hanger Replacement of Tied-Arch Bridges with Rigid Bars

The construction of bridges with suspenders, such as cable-stayed or tied-arch bridges, needs deep study of the prestressing forces to be applied to stays or hangers in all stages, depending on the construction technique adopted. In these cases, the main issue is the determination of the initial forces and optimization of the prestressing system in terms of stressing values and sequence. When the bridge is already built and suspenders have to be replaced for maintenance, a different problem has to be faced by the engineer, because the sequence of replacements and the values of the axial stresses depend very much on the service conditions of the bridge and on its historical evolution from construction to maintenance. Furthermore, the technique used for the original suspension system is fundamental in designing the replacement intervention. In this paper hanger replacement of tied-arch bridges with rigid bars is focused on, inspired by an actual case of a steel bridge of medium span in which replacement of the hangers for the entire suspension system was demanded by the high state of corrosion. This posed the problem of how to replace the hangers, which stressing sequence was the most suitable, together with evaluation of the choices made in the original design for the suspension system, which did not provide for the possibility of calibrating the state of tension through onsite adjustments of hanger prestress. Assessment of the stressing sequence for hanger replacement is presented and discussed and the results of the study performed in the actual case study are shown.