Bowen Zeng,  and Yong Li

Bowen Zeng, Department of Civil and Environmental Engineering, University of Alberta, Edmonton, AB, Canada., bzeng1@ualberta.ca
Yong Li, Assistant Professor, Department of Civil and Environmental Engineering, University of Alberta, Edmonton, AB, Canada., yong9@ualberta.ca

ABSTRACT
Detailed finite element modeling of masonry structures is essential to understand their complex mechanical behavior accounting for different failure mechanisms, which highly depends on the mortar joints (i.e., mortar layer and unit-mortar interaction). As such, this study presents a plasticity-based constitutive model for a 3D interface element that is capable of capturing various failure modes of mortar joints, including tension cracking, shear sliding, and compressive crushing. It is characterized by two hyperbolic yield surface criteria: tension-shear failure surface and compressive cap surface. The evolutions of the yield surfaces and state variables are formulated based on the concept of strain-softening/hardening. A fully implicit Euler Backward integration algorithm, combined with a local-global Newton-Raphson (NR) solver, is adopted to achieve the predictor-corrector returning mapping procedure in the numerical formulation. Additionally, the variations of dilatancy and fracture energy are introduced, aiming to describe the mechanical behavior of mortar joints accurately. The model is implemented in the finite element software Abaqus via UMAT. The proposed interface model is validated with the unit-mortar-unit assemblages and unreinforced masonry walls. The capability of newly developed interface model shows its potential to be used to further explore the mechanical behavior of masonry structures.

KEYWORDS: finite element modeling, interface element, implicit integration algorithm, masonry structures