In the proposed model, similar to the approach presented in [1] for the in-plane nonlinear analysis of single-leaf masonry panels, the blocks are modelled using continuum elements, while the mortar and brick-mortar interfaces are modelled by means of nonlinear interface elements. Compared to previous models which used two-dimensional continuum elements and one-dimensional nonlinear interface element, the proposed approach employs three-dimensional continuum solid elements and two-dimensional nonlinear interface elements. Not only does this enable the representation of any three-dimensional arrangement for brick-masonry, as both the in-plane stacking mode and the through-thickness geometry are taken into account, but also it allows the investigation of both the in-plane and the out-of-plane response of unreinforced masonry panels.

A novel two-dimensional cohesive interface element has been developed, which accounts for both geometric and material nonlinearity. A co-rotational approach is employed, where a local reference system which follows the interface mid-plane is defined. According to this approach, the effects of geometric nonlinearity are determined through transformations between global and local entities [2]. The internal forces through the interface are modelled by means of an elasto-plastic material law which follows a Coulomb slip criterion, considering energy dissipation, decohesion and residual or frictional behaviour. In order to account for dilatancy, arising from the roughness of the fracture surface, a non-associated plastic flow is assumed, where a plastic potential different from the yield function is introduced. The procedure developed by Caballero et al. [3] for solving the nonlinear equations due to material nonlinearity has been employed, as it offers enhanced performance for large scale mesomechanical three-dimensional simulations.

Finally, some numerical results are presented, providing experimental-numerical comparisons for the in-plane and out-of-plane static behaviour of brick-masonry panels. The results achieved demonstrate the significant potential of the proposed approach but also the need of improvement in the constitutive model to capture the various relevant failure phenomena for masonry.

1

P.B. Lourenço, J.G. Rots, "Multisurface Interface Model for Analysis of Masonry Structures", Journal of Engineering Mechanics (ASCE), 123(7), 660-668, 1997. doi:10.1061/(ASCE)0733-9399(1997)123:7(660)

2

B.A. Izzuddin, "An enhanced co-rotational approach for large displacement analysis of plates", Int. J. Numer. Meth. Engrg., 64, 1350-1374, 2005. doi:10.1002/nme.1415

3

A. Caballero, K.J. Willam, I. Carol, "Consistent tangent formulation for 3D interface modelling of cracking/fracture in quasi-brittle materials", Comput. Methods Appl. Mech. Engrg., 197(33-40), 2804-2822, 2008. doi:10.1016/j.cma.2008.01.011

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