Theoretical foundations for design of reinforced concrete under plane stress states

The plane stress state occurs in beam walls in the zone of action of shear forces, column consoles, shear walls, slabs, shells and many other reinforced concrete structures. When calculating the strength of such structures, various, sometimes different from each other, theoretical approaches and design methods are used, based, in a number of cases, on empirical dependencies. At the same time, there are real prerequisites for the creation of methods for design the strength of reinforced concrete elements under a plane stress state based on a unified approach based on the theory of concrete plasticity and taking into account the presence, position, intensity, stress state and strength characteristics of the reinforcement. This paper presents the theoretical foundations for design the strength of reinforced concrete elements based on the theory of concrete plasticity and consideration of reinforcement as an internal connection that ultimate transverse deformations of concrete under compression, causing the occurrence of reactive compressive stresses. Calculation dependencies have been obtained for determining the ultimate stresses in a reinforced concrete element under axial compression, plane stress state compression-compression, compression-tension when stresses are transferred directly to concrete or through stretched reinforcement, which take into account the strength characteristics of concrete, content, position and strength characteristics of reinforcement. The graphs are given that allow to estimate the influence of the listed factors on the value of ultimate compressive stresses in concrete. The developed theoretical approach is extended to the design of the strength of compressed elements with welded mesh reinforcement and the possibility of its use for the design of similar elements with confinement reinforcement, as well as pipe-concrete elements, is shown.