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In this paper, the behavior of RC beams deficient in shear capacity and strengthened by using post-tensioning technique was investigated by conducting flexural tests on over twenty-four beams. The beams were 80x 150 mm in cross
section and 1800 mm long. Test variables I
Delude: concrete strength (fc') ; shear span to effective depth ratio (a/d); longitudinal
tensile reinforcement (p); level of post tensioning as a percontage of fc' ; presence of shear reinforcement; use of continuous
plates, and presence of shear crack. Beam specimens were made with fc' of 35 and 50 MPa, shear span of L/4 and L/6, and
reinforcement ratio based on seismic design. The level of post - tensioning in
location of shear crack potential is 0.04 fc' and 0.07 fc'. Test results indicate
that a post-compression stress as low as 0.04 fc' in shear critical region increases shear strength significantly. It also changes failure mode from brittle shear to ductile
bending. Moreover, influence of other
parameters is very limited at this level of post-compression. Theoretical evaluation of behavior of beams strengthened in the critical region is based on Mohr's theory.
The analysis shows that this method of
strengthening is very effective, and is capable of providing ductile flexural behavior in beams with inadequate shear strength.