Abstract
With the aim to study the flexural behaviour and ultimate strength of post-tensioned prestressed. concrete beams, statical tests were performed on 12 rectangular prestressed concrete beam using 1-φ24mm steel in bar form. The objective of study was to provide direct and quantitative comparisons of the flexural behaviour and strength of beams with four types of tension reinforcement: (1) 1-φ24mm post-tensioned grouted steel bar with the prestress of 20 ton, 25 ton and 30 ton, respectively, (2) 1-φ24mm post-tensioned. grouted steel bar tensioned up to 25 ton, with additional 2-φ12mm or 3-φ12mm deformed bars, (3) 1-φ24mm post-tensioned nongrouted steel bar tensioned up to 25 ton, with additional 2-φ12mm or 3-φ12mm deformed bars, (4) 1-φ24mm post-tensioned grouted steel bars connected by a coupler. The characteristics of these types of beams were compared as to cracking load, load-deflection, relationship, deflection recovery, ultimate deflection, flexural rigidity and ultimate flexural strength. Following results were obtained from test data. (1) Initial cracking load was increased with the increase of effective prestress transferred, regardless of effects of non-stressed deformed bars, bonded or unbonded prestressed steel bar and bonded steel bar with a coupler. (2) Adding the non-stressed deformed bars to the unbonded beams, the flexural rigidity after cracking approached to those of bonded beams. (3) All of the test beams, bonded or unbonded, showed about 90 percent recovery of deflections even after the beams had been loaded to approximately 95 percent of the ultimate load, (4) Referring to the midspan deflection at failure load, the definite differences were not found among four types of beams, bonded or unbonded and with or without additional deformed bars. (5) The beams without additional bars showed nearly same ultimate strengths, which were 30-50 percent lower than those of bonded or unbonded beams with additional bars. Also, obvious differences in strength between the bonded and unbonded beams with additional bars were not recognized. (6) The use of bonded steel bars with a coupler gave no injurious effects on the flexural behaviour and also on the ultimate strength of beams.
