Assessment of Direct Tensile Strength of Concrete

Abstract

Tensile strength is one of the important strength parameter of concrete. Tensile strength of concrete is of prime importance in case of water retaining structures, runway slabs, pre-stressed concrete members, bond and shear failure of reinforced concrete members and cracking of mass concrete works. Concrete members and structures that transmit loads primarily by direct tension rather than bending include bins and silos, tanks, shell, ties of arches, roof and bridge trusses and braced frames. Members such as floor and roof slabs, walls, and tunnel linings may also be subjected to direct tension as a result of restraint of volume change. Much investigation is done upon evaluation of tensile strength of concrete by indirect methods and comparatively fewer efforts have been made for its assessment by direct method. Assessment of direct tensile strength of concrete must be reliable than the strength measured by indirect tension tests. The measurement of concrete under tension by the indirect methods provides approximate strengths. This is because the tensile strengths are evaluated on the assumption that the concrete is linearly elastic until failure, while in reality, the stress-strain curve becomes nonlinear when the concrete is close to failure. Tensile strength evaluated by the direct tension method provides values which is closer to the true tensile strength of concrete. For the direct tensile strength of concrete proper arrangement must be use which ensures the uniaxial tensile load and uniform stress distribution on the specimen. In the present study specimens for direct tensile strength, cubes for compressive strength, cylinders for split strength and beams for flexural strength are cast of concrete grades M20, M30, M40 & M50 for plain concrete as well as steel fiber reinforced concrete. The direct tensile test specimens are of dumbbell shaped. For the uniaxial tension load on dumbbell shaped specimen a new experimental set-up frame has been developed. The strength results are correlated to develop the relationships amongst direct tensile strength, split cylinder strength, flexural beam strength and compressive strength.