INFLUENCE OF STEEL FIBERS AND COMPRESSION REINFORCEMENT ON DEFLECTIONOF HIGH-STRENGTH CONCRETE BEAMS

The paper presents an experimental and theoretical study on immediate and long-term deflections of high-strength concrete beams. Twelve beam s with 85 MPa (12,300 psi) compressive strength and having tension and compression rebars and steel fibers were tested. The experimental res ults show that the addition of fibers increases the flexural rigidity of the beams thus reducing the immediate and total long-term deflectio ns under sustained service load. The beneficial effect of the compress ion reinforcement in controlling the long-term deflection is observed in beams without fibers. However for beams having steel fibers and com pression reinforcement, the behavior depends on the amount of the two types of reinforcement, and their excessive amount may have an inauspi cious effect on the long-term deflection. A method is presented for co mputing the effective moment of inertia of fibrous concrete beams and a modification is suggested to the long-term multiplier of the ACl Cod e to include the effect of fibers and high-strength concrete.