Triaxial elastoplastic damage constitutive model of unreinforced clay brick masonry wall

Due to differences in the properties of composition materials and construction techniques, unreinforced masonry is characterized by low strength, anisotropy, nonuniformity, and low ductility. In order to accurately simulate the mechanical behavior of unreinforced brick masonry walls under static and dynamic loads, a new elastoplastic damage constitutive model was proposed and the corresponding subroutine was developed based on the concrete material constitutive model. In the proposed constitutive model, the Rankine strength theory and the Drucker-Prager strength theory were used to define the tensile and compressive yield surface function of materials, respectively. Moreover, the stress updating algorithm was modified to consider the tensile plastic permanent deformation of masonry materials. To verify the accuracy of the proposed constitutive model, numerical simulations of the brick masonry under monotonic and cyclic uniaxial tension and compression loads were carried out. Comparisons among the numerical and theoretical and experimental results show that the proposed model can properly reflect the masonry material mechanical properties. Furthermore, the numerical models of four pieces of masonry walls with different mortar strengths were established. Low cyclic loadings were applied and the results show that the proposed constitutive model can properly simulate the wall shear failure characteristics, and the force-displacement hysteretic curves obtained by numerical simulation are in good agreement with the tests. Overall, the proposed elastic-plastic damage constitutive model can simulate the nonlinear behavior of unreinforced brick masonry walls very well, and can be used to predict the structural response of masonry walls.