Discontinuum analysis of the fracture mechanism in masonry prisms and wallettes via discrete element method

Abstract

This study proposes an alternative approach to modeling the failure mechanisms of brickwork assemblages under combined shear-compression, shear-tension (parallel to bed joints), and compression-flexural loadings using the discrete element method (DEM). In this context, recently developed elastic-softening contact constitutive laws considering the mode-I and mode-II fracture energies are implemented into the dynamic solution scheme of the DEM to simulate the mechanical interaction between mortar and masonry units represented via 3D polyhedral blocks. Different experimental studies from the literature are used to validate the proposed computational models, and good agreement is found in terms of strength, material behavior, and fracture mechanisms. The findings of this research indicate that the proposed modeling strategy is successful in predicting the macro behavior of masonry under various complex fracture modes based on the defined micro properties. Sensitivity analyses are also performed by varying the fracture energy and valuable inferences are made with respect to the stress-displacement response and failure mechanisms of masonry.

Tensile Fracture Mechanism of Masonry Wallettes Parallel to Bed Joints: A Stochastic Discontinuum Analysis

“…Fundamentally, DEM was developed to explore the mechanical behavior of the discontinuous systems by considering them as an assembly of rigid and/or deformable blocks, interacting with each other through the contact points. Deformability of the blocks is introduced by constant strain In a preceding study by the authors, Pulatsu et al [6], a deterministic modeling strategy was used to explore the tensile behavior of the masonry wallettes using average contact properties. The contribution of the present study furthers this investigation and explores the effect of statistically varied contact properties.…”

“…The elastic response of the contact is controlled by the orthogonal springs both in the normal and shear directions, based on the assigned contact stiffness k n and k s , respectively; whereas the post-peak behavior is governed by the nonlinear parameters, namely tensile strength ( f T ) defined in the normal direction and cohesion (c) as well as the friction angle (φ) in the shear direction (see Figure 2). In the present study, semi-rigid blocks are used considering relatively high stiffness at the finite-difference zones (i.e., 10 times macro elastic stiffness) to lump the linear and nonlinear displacements at the joints as performed in relevant studies [3,6,13]. Therefore, deformations develop at the joints (i.e., along the boundaries of adjacent polyhedral blocks) instead of within the block domain and block deformations have negligible influence on the macro stress-displacement behavior of the system.…”

“…To address this gradual degradation and the corresponding decrease in the load carrying capacity of the material, nonlinear contact constitutive models are implemented in 3DEC to be utilized in tension and shear failure criteria considering exponential softening functions ( Figure 4). The mathematical formulations of the exponential functions, given by Lourenço et al [21], and further details about the contact models can be found in the related study [6]. It is important to note that the Coulomb slip joint model is utilized in the shear direction, where the maximum and residual shear strengths are calculated as written in Equation 5, and the descending Throughout this research, a commercial discrete element code 3DEC, developed by Itasca, is used, where the custom contact constitutive models are adopted into the software (3DEC) via a user-defined constitutive model option [16].…”

“…Hence, utilizing the discontinuum representation of masonry, this research aimed to better understand the influence of material properties in masonry wallettes on the fracture mechanism and stress-displacement behavior, subjected to tension parallel to bed joints. In a preceding study by the authors, Pulatsu et al [6], a deterministic modeling strategy was used to explore the tensile behavior of the masonry wallettes using average contact properties. The contribution of the present study furthers this investigation and explores the effect of statistically varied contact properties.…”

“…Figure A1. Influence of block-size on the capacity and stress-displacement response, Left: failure mode I; Right: failure mode 2 (taken from [6]).…”