Strengthening of RC Continuous Beams by External Prestressing

This paper presents the test results on 12 two-span continuous T-beams strengthened using different external tendon types and profiles and subjected to third-point loadings. Test results indicated that an increase in ultimate strength with sufficient ductility could be achieved using short tendons located over the critical sections. Such a strengthening scheme led to a more ductile beam behavior compared to those with continuous tendons over both spans or with draped tendons within each span. Parabolic tendons anchored beyond the interior support however effectively strengthened the negative moment region with improved ductility at ultimate limit state. Furthermore, beams strengthened with carbon fiber-reinforced polymers tendons showed similar response to those with steel tendons, while beams subjected to unsymmetrical loading suffered from larger deflections and lower ultimate load compared to those subjected to symmetrical loading. Theoretical predictions based on the concept of bond reduction coefficients were found to agree with the test results. Finally, a parametric study was carried out to establish design charts that can be used for the strengthening of continuous beams. A design example is presented to illustrate the use of the charts.