Beam strengthening by external post-tensioning: Design recommendations

Abstract

Buildings and bridge structures are often in need of strengthening due to deterioration of material properties or a change in design loads. External post-tensioning, in which tendons are installed on the outside of a structural member with the aid of deviators and anchorages, is an attractive strengthening method as it does not add much weight and can be carried out with minimal disruption to the operational function of the structure. An extensive programme has been carried out on simple-span and continuous beams as well as beams in reinforced concrete frames to study the effect of tendon configuration, second-order effects, and secondary and tertiary effects due to external post-tensioning. The effect of external post-tensioning on shear capacity and the use of fibre-reinforced polymer prestressing cables were also examined. This paper highlights the main findings of the study, based on which design recommendations are given and a direct design approach is proposed.