Continuous Beams with Prestressed Reinforcement

Test data from four continuous rectangular beams, imply supported over two 15-ft spans are reported. The only variable in the test is the relative amount of deformed steel bars and precast prestressed concrete prisms used as tension reinforcement over the intermediate support. Use of prestressed reinforcement at intermediate support regions of beams, controls crack development and propagation at those locations and improves the overall flexural rigidity. Optimum results are obtained when prestressed reinforcement is used shortly after they are cast, when they are placed as close as possible to the extreme tension fiber, and when they are accompanied by a small amount of nonprestressed reinforcement. Plastic curvatures at a hinging region may be considered to extend over a distance equal to the effective depth of the beam plus the width of the distributing plate. Hinge rotations and moment redistribution are not influenced by the relative prestressing index ratio. Because of their better serviceability criteria, beams with prestressed reinforcement could be allowed higher design percentage moment redistribution.