Increasing the Capacity of Existing Bridges by Using Unbonded Prestressing Technology: A Case Study

External posttensioning or unbonded prestressing was found to be a powerful tool for retrofitting and for increasing the life\udextension of existing structures. Since the 1950s, this technique of reinforcement was applied with success to bridge structures\udin many countries, and was found to provide an efficient and economic solution for a wide range of bridge types and conditions.\udUnbonded prestressing is defined as a system in which the post-tensioning tendons or bars are located outside the concrete crosssection\udand the prestressing forces are transmitted to the girder through the end anchorages, deviators, or saddles. In response to\udthe demand for a faster and more efficient transportation system, there was a steady increase in the weight and volume of traffic\udthroughout the world. Besides increases in legal vehicle loads, the overloading of vehicles is a common problem and it must also\udbe considered when designing or assessing bridges. As a result, many bridges are now required to carry loads significantly greater\udthan their original design loads; and their deck results still deteriorated by cracking of concrete, corrosion of rebars, snapping of\udtendons, and so forth. In the following, a case study about a railway bridge retrofitted by external posttensioning technique will be\udillustrated