A shear-friction truss model for reinforced concrete beams subjected to shear.

摘要

The objective of this thesis was first to develop a model to calculate the shear transferred across an inclined crack, and second to determine the effective strength of concrete in the web of a beam when diagonal crushing of concrete governs. Fifty-seven tests were carried out to aid in the development of this objective.;The experimental program included two series of tests. The first series consisted of seventeen concrete cantilevers tested to investigate the shear-friction on an inclined crack. The major variables were the angle of the inclined crack, the longitudinal compressive force and the conditions of the crack interface. The specimens generally failed due to the loss of the shear transfer across the crack interface. The ratio of the shear transferred by shear-friction across the inclined cracks to the longitudinal compression force on the crack face increased as the angle of inclination of the failure crack increased. The ratio varied from 0.114 to 1.778.;Based on the tests, a shear-friction truss model was developed. In this model the function of the stirrups is represented by the truss analogy and the concrete contribution is modelled by shear-friction. Both the truss model and the shear-friction model are based on a constant angle of the inclined crack. The shear-friction truss model was used to examine twenty seven test beams and gave a good prediction of the shear strength of the beams. Based on the shear-friction truss model, a design procedure for shear was developed.;The second series of tests consisted of forty concrete panels subjected to longitudinal compression and transverse tension. The major variables were the gross transverse tensile strain and the loading history. The specimens generally failed due to longitudinal crushing. It was found that the effective compressive strength decreased as the gross transverse tensile strain increased. The loading history had no effect on the effective compressive strength of concrete. The decrease in compressive strength was caused by the number and the width of the cracks in the concrete. Because the gross transverse tensile strain is a measure of the cracks in the concrete, the effective compressive strength of the concrete is expressed as a function of the gross transverse tensile strain. A new equation for the principal tensile strain in the web of beam was derived based on the strains in a compression field. A constant efficiency factor of 0.75 is recommended in the shear design of slender beams.