3D axial symmetric constitutive model improved with variance

A 3D axial symmetric orthotropic constitutive model for concrete improved with variance is proposed in order to make the result of finite element analysis more accurate. According to the concept of the equivalent uniaxial strain proposed by Darwin and Pecknold, on the base of the 3D axial symmetric orthotropic model of Elwi and Murry's, a new 3D axial symmetric orthotropic model is proposed for concrete. It is different from the model of Elwi and Murry's in that subsidiary elements of the constitutive matrix are obtained on principle of minimum variance of computed results with experiments. Compared with Elwi's model, the computed result of the new model is in better agreement with experimental results. Thus, the proposed model here is more accurate and is applicable to 3D axial-symmetric nonlinear finite element analysis of various reinforced concrete members. The method improving constitutive model with variance can be applied to 2D and 3D model too. The new discriminatory rule for principal stress rotation is simple, applicable and can avoid abrupt change of computed result.