Strengthening of precast concrete girder bridges by post-tensioning for continuity

Simple-span precast concrete girders have frequently been used I in bridge superstructures. However, to accommodate today's heavy traffic loads, their carrying capacity can be strengthened by providing moment continuity between adjacent spans. This study investigates the use of external tendons to provide partial continuity. It is shown that such a strengthening scheme results in stiffer beam response than individual spans. The effective tendon force governs the beam deflections and opening of the joint between adjacent spans. An analytical method is presented to predict the piece-wise linear response of two-span continuous beams derived from two simple-span beams. Good agreement of both the calculated deflections and widths of joint opening with the observed test results was obtained. Based on a parametric design study, charts are provided for strengthening precast simple-span beams using external prestressing. A design example illustrates the proposed method.