ABSTRACT
Shear failure of conventional reinforced and prestressed concrete beams usually occurs by tensile failure of concrete in the shear span. Shear failure is brittle in general. To prevent this type of failure and to increase the shear strength, shear reinforcement in the form of stirrups is incorporated. Steel fibres act as substitutes for shear reinforcement and especially in case of thin webs where bending and fixing of bars is difficult. In addition because of the uniform distribution of fibres and its random orientation through out the volume of concrete uniform effective reinforcement is automatically established, thereby providing a substantial improvement in the resistance to the formation and growth of cracks besides enhanced ductility and better spalling resistance.
The paper presents the results of investigations undertaken on the effect of steel fibres on the behaviour and strength of fibre reinforced prestressed concrete beams (with Para-bolic cables) under shear. Tests were carried out on eight post tensioned beams, including two companion bonded and unbonded prestressed beams without fibres. Both bonded and unbonded beams studied at different contents ranging from 0% to 0.75%. The fibrous prestressed beams showed marked improvement in first crack load and ultimate load over that of plain prestressed concrete beams.
The theoretical prediction of ultimate shear strength from a knowledge of the fiber properties, the cube strength, amount of tensile reinforcement and the applied prestress has been compared with experimental results. The predictions obtained by the theoretical method were found to be satisfactory.
