Behavior of bonded and unbonded prestressed normal and high strength concrete beams

The major disadvantage of using ordinary reinforced concrete (RC) elements is the corrosion of steel, which occurs due to effect of cracks in tension zones. The main advantage of the fully prestressed concrete system is the absence of cracks in the concrete at the nominal service load and therefore better durability will be achieved. Combining the PC system with the use of high strength concrete is a milestone, which will potentially result in a new design approach. The disadvantage of the use of this combination is referred to the reduced ductility of concrete members.This paper presents an experimental program conducted to study the behavior of bonded and unbounded prestressed normal strength (NSC) and high strength concrete (HSC) beams. The program consists of a total of nine beams; two specimens were reinforced with non-prestressed reinforcement, four specimens were reinforced with bonded tendons, and the remaining three specimens were reinforced with unbonded tendons. The overall dimensions of the beams are 160 × 340 × 4400-mm. The beams were tested under cyclic loading up to failure to examine its flexural behavior. The main variables in this experimental program are nominal concrete compressive strength (43, 72 and 97 MPa), bonded and unbonded tendons and prestressing index (0%, 70% and 100%). Theoretical analysis using rational approach was also carried out to predict the flexural behavior of the specimens. Evaluation of the analytical work is introduced and compared to the results of the experimental work.