Abstract
The motivation of this research is driven by the need for an efficient and accurate nonlinear modelling method for the analysis of unreinforced masonry infill walls, particularly their influence on the behaviour of frame buildings. In this modelling approach the nonlinear behaviour of masonry material is simulated by an anisotropic material model, and the detachment between masonry walls and surrounding frames, leading to a boundary condition nonlinearity, is taken into account. In addition, the geometric nonlinearity caused by out-of-plane loadings is considered.
Two strategies for modelling the infill walls are studied, and their benefits and drawbacks in different applications were reviewed. The microscale modelling dealing with simulating the constituents of masonry individually, e.g. units and mortar, at two detailed and simplified levels, are discussed and the latter is then utilised for the verification of the models presented in this research. The macroscale modelling, considering the masonry wall as a smeared crack continuum, is then elaborated and an anisotropic material model, previously presented for plane stress condition, is adapted for a plate bending application. This nonlinear material model utilises two different failure criteria in tensile and compressive regimes, and determines stresses and strains in a plastic range using a return mapping algorithm.
A novel interface element is formulated to reproduce the more realistic behaviour of infilled frames by taking into account the nonlinearity caused by variation of boundary conditions. This element simulates the separation between infill walls and surrounding frame, while a newly defined co-rotational local reference system facilitates the treatment of geometric nonlinearity. The interface element is coupled with a previously developed constitutive material model to be able to deal with material nonlinearity. The new features of this element, including rotational DOFs in nodes, also enable it to accompany shell elements for plate bending problems with large displacements. These characteristics create an effective modelling method for in-plane and out-of-plane loads.
The proposed method is finally employed in a model of infill frame to demonstrate the accuracy of the method in predicting various failure mechanisms in infill walls.