Strengthening of Reinforced Concrete Bridges by External Prestressing

The lack of maintenance along with the increase of the weight of (Brazilian) road vehicles require the strengthening of bridges in Brazil. Rehabilitation techniques and structural reinforcement can make this strengthening technically and financially viable. However, since there are no specific rules on how to carry out this type of analysis in Brazilian bridges, or procedures for the calculation of specific reinforcements, several methods are not considered while choosing the type of structural reinforcement, and neither the right efforts are taken for a proper assessment. This work studies the flexural reinforcement of structures in reinforced concrete by external prestressing, exposing advantages and disadvantages of its use and the characteristics of this reinforcement method. Finally, a calculation methodology is proposed employing a theoretical example of structural reinforcement of an old Brazilian bridge by external prestressing with the use of lubricated steel wire ropes, reinforced concrete deviators and anchor blocks. In order to base the calculation the rules of the bridge project were used to find the project efforts and the existing steel area. Based on the current standards and the bridge expansion project, new efforts were determined on the main beams. Considering these new efforts and the existing steel area, the necessary prestressing steel area was determined so that along with the existing passive steel rebars the bridge can withstands the new traffic conditions