A nonuniform hardening plasticity model for concrete materials

For the most part, the developments of constitutive models for for the concrete by the theory of plasticity have in the past been made to scarch for a suitable failure surface. The initial yield surface is usually assumed to have the same shape as the failure surface but with a reduced size. The subsequent loading surfaces are then obtained by the uniform expansion of the initial one. This approach is found generally inadequate in predicting the deformational behavior of concrete for a wide range of loading conditions. The present non-uniform hardening plasticity model adopts the most sophisticated failure model of Willam-Warnke or Hsieh-Ting-Chen as the bounding surface; assume an initial yield surface with a shape that is different from the failure surface; proposes a nonuniform hardening rule for the subsequent loading surfaces with a hydrostatic pressure and Lode-angle dependent plasticity modulus; and utilizes a nonassociated flow rule for a general formulation. The work-hardening stress-strain behaviors of concrete based on the present model are found in good agreement with experimental results involving a wide range of stress states and different types of concrete material. The important features of inelastic behavior of concrete, including brittle failure in tension; ductile behavior in compression; hydrostatic sensitivities; and volumetric dilation under compressive loadings can all be represented by this improved constitutive model.