Strength of webs of I-shaped reinforced concrete elements under shear forces

Abstract

All existing methods for calculating the strength of reinforced concrete elements are based on experimentally established possible types of element failure under certain forces caused by external forces. Thus, under the action of bending moments or the combined action of moments and longitudinal forces, failure occurs as a result of the crushing of the concrete in the compressed zone when the stresses in the longitudinal reinforcement reach or do not reach the limit values for tension (yield strength) and compression. under the action of torsional moments – along a critical spiral crack, when a compressive force is applied over a small area – from the crushing  of concrete under the area. The resistance of reinforced concrete elements to shear forces differs significantly from other forces of action, as it is characterized by different types of failure – concrete fragmentation above a critical inclined crack, concrete shear above a critical inclined crack, crushing of concrete in an inclined strip between inclined cracks or a support and a load, loss of adhesion of longitudinal reinforcement to concrete in the tension zone beyond a critical inclined crack, and failure along inclined cracks during punching, which is explained by the influence of the loading pattern, the geometry and design features of the element. Accordingly, to assess strength in the event of possible types of failure, the appropriate calculation tool is used, which is not always implemented within a single calculation model for elements. Therefore, in practice, different calculation methods are used for each of the possible types of failure.

This paper presents a method for calculating the strength of I-beam reinforced concrete webs when they fail along a strip between inclined cracks, based on the principles of reinforced concrete plasticity theory, considering the concrete of the web under conditions of plane stress compression-tension when tensile stresses are transferred to the concrete from shear reinforcement. Within the framework of the developed method, the criterion for failure is taken to be the attainment of the main compressive stresses in the concrete strip of the web at the corresponding stress state. The general case of the ultimate equilibrium of a beam within the strip between inclined cracks with arbitrary content and location of transverse reinforcement is considered. Calculated dependencies are obtained for calculating the limit values of stresses in the strip and shear force at wall failure.