Restoration of 45 Years Old PSC Bridge by External Post Tensioning

The use and advantages of Post Tensioning are very well known in the Civil Engg Industry as it has been in use for the last 40 to 50 years. Post tensioning is one of the best methods to induce stresses in the concrete before application of Live load and this technique can also be widely used for Restoration and Rehabilitation of Structures. Unlike the use of Post-Tensioning in new structures there are no definite methods or codes for application in Restoration and Rehabilitation of Structures. For restoration and rehabilitation of structures, we need to improvise the PT technique in combination with other techniques and materials available. Therefore our imagination is our limitation.

This paper deals with restoration of a PSC bridge constructed in 1968 and in service since then. As part of the 4 laning of Highway between Hungund and Hospet towns of Karnataka State, it is proposed to construct parallel bridges of 2 lanes at K M 291 & 292 on the downstream of Tungabhadra Dam and investigate the suitability of the existing bridges for use for the two lanes. Detailed Non-Destructive tests and Design analysis have been carried out on the superstructure and it was concluded that the existing 19 span & 16 span structures are suitable for present day traffic and design consideration, however in each of the bridge damage in form of exposure of PT cables/snapping was observed in one of the end girder (in 7 spans of each of the bridge). In view of the same, restoration measures were carried out to the 7 spans in each of the bridges using external Post-Tensioning Technique. Being a structure with active stresses it is prudent to use Post Tensioning technique as a passive strengthening technique would not be very effective for active structure.

Various aspects of Design of the scheme and intricacies of practical execution of the system are highlighted in the paper. This is one of its kind of restoration carried out on a 45 year old structure. It was not only challenging to design the system but also had to improvise many techniques during execution of the project. The structure was load tested after the restoration.