Experimental Study on Damaged Prestressed Concrete Beams Using External Post-Tensioned Tendons

This paper focused on flexural behavior of damaged partially prestressed concrete beams strengthened with external post-tensioned tendons. A total of six strengthened beams and two unstrengthened beams, serving as control specimens, were tested to failure. The test parameters were prestressing tendon types (steel and carbon fiber-reinforced polymer [CFRP]) and initial damage levels (undamaged, in-service damage, and over-loaded damage). The test results revealed that strengthening the beams with external tendons could successfully improve serviceability and ultimate flexural capacity with good deformability. Additionally, the initial damage had slight effect on ultimate capacity and ductility, but it did affect the cracking and deflection behavior. The ductility of the strengthened beams using external CFRP tendons was comparable to those using steel strands. Finally, the experimental results were compared to theoretical predictions obtained from several design approaches, indicating that the flexural capacity of the strengthened beams with initial damage can be analyzed in the same way as those without initial damage, whereas the effect of initial damage should be considered in calculating the deflection of the beams with overloaded initial damage.