The effect of varying the pre-tension and area of reinforcement on the ultimate bending strength of concrete beams

Abstract

Summary Tests on eighteen pre-tensioned concrete beams are reported. The beams were cast in groups of three, the members of anyone group differing only in the amount of pre-tension. The percentage of reinforcement varied between groups but was always sufficient to preclude failure by steel rupture. Two series of tests were made. In the first, three groups of three beams were made and tested by the author who used an extreme range of pre-tension. The second series was made and tested independently by Mr F. C. H. Nisbet, who repeated the author's tests in respect of beam dimensions and percentage of reinforcement, but who used rather higher concrete strengths and a more practical range of pre-tension.(1)* The beams were all 4 in. deep with an effective depth of 2½ in. Two widths were used: 1⅛ in. and It in. The length between supports was 45 in. and under four-point loading the central 15 in. was subjected to a uniform bending moment. Both the area of steel and the degree of pre-tension were found to have an appreciable effect on the bending strength of the beams.