MODELLING THE TENSILE BEHAVIOR OF PLAIN CONCRETE UNDER FLEXURAL LOADING

The tensile behavior of plain concrete is customary assumed to be linear, and the stiffness modulus is approached by the value of the initial tangent stiffness modulus in compression. However, even two decades ago the contrary was proven by the experimental results on plain concrete in direct tension. The stress-strain behavior of concrete in tension was demonstrated to be highly non-linear, even at very low stress levels. One of the major difficulties in obtaining an accurate tensile stiffness response is to achieve a uniform tensile stress in the section, without creating stress concentrations at any point along the section. These stress disparities will lead to micro crack initiation and falsely recorded responses. A non-linear Finite Element Model (FEM) based on the anisotropic material approach, was developed to produce the load-displacement response of a concrete beam loaded with a two point loading system. The load-displacement curves and stress-strain curves were validated to laboratory tested specimens having identical material properties. It was shown that the stiffness behavior of plain concrete in flexure is non-linear, and follows a quadratic function. The research work also covered the evaluation of two failure criteria