In this paper, a strain space plasticity model has been proposed to represent the softening as well as hardening behavior of concrete materials. Unlike the stress space plasticity theory based on the Drucker's postulate, the strain space formulation based on the Il'yushin's postulate gives a clear distinction of loading, neutral loading, and unloading. The general strain space formulation has been presented in some details by introducing the loading function F and the plastic potential function G in the strain space. The incremental stress strain relation has been given in a tensorial form. Using the experimental data available from triaxial compression tests, the model parameters have been determined and then model simulation has been performed to demonstrate the model capability. It has been confirmed that the proposed model can predict sufficiently the softening as well as hardening behavior of concrete materials.
