A virtual microstructure generator for 3D stone masonry walls

Detailed micromodel simulations of stone masonry walls require as input a 3D mesh that represents a realistic arrangement of stones in the masonry wall. In this paper, we constructed the first 3D masonry microstructures to derive 2D and 3D finite or discrete element meshes for a large range of stone and brick masonry typologies. The generation process was treated as a constraint many-objectives packing optimisation problem, which was designed to mimic the building process of a mason. The generated walls were compared qualitatively and quantitatively with real stone masonry samples of regular and irregular typologies. The Python3.7 codes of the microstructure generator and the generated meshes shown in this paper are all made available under GNU LGPLv3 terms and conditions. The techniques in this paper for generating 3D meshes of stone masonry walls will serve as input for simulations of individual walls, multiscale analyses of entire structures as well as for homogenisation techniques.

Equivalent frame models for in-plane and out-of-plane response of unreinforced masonry buildings

Francesco Vanin

The seismic assessment of masonry buildings, both modern unreinforced masonry (URM) buildings and historical heritage constructions, is a complex task, characterised by a several sources of uncertainty, which regard the appropriate modelling of strategy the problem, the model parameters, and the seismic input. In order to properly account for all sources of uncertainty and provide a robust risk estimate, simple models to be run under different conditions are necessary. In this regard, equivalent frame modelling of masonry buildings is a modelling approach which can produce reliable estimates of the seismic demands, in terms of displacement and accelerati, for buildings showing a predominant in-plane failure mode. The simplicity of the approach allows performing multiple simulations at a reasonable computational cost. This thesis concentrates on the extension of the equivalent frame approach for the modelling of both the in-plane and the out-of-plane response of masonry buildings. Making use of the computational simplicity of equivalent frame models, it further proposes an approach for the probabilistic assessment of buildings, which aims at being potentially applicable also outside the research domain, to which probabilistic methods are mainly confined at the state of the art. In order collect information on the uncertainties related to the assessment of the in-plane behaviour of masonry, with a particular regard to stone masonry, a database of 128 shear compression tests on walls was collected and analysed. Distributions and median values of the most relevant material properties were derived, including the displacement capacities at cracking, yielding, maximum force capacity, significant damage and collapse limit states. Moreover, the uncertainty on the determination of force capacity and stiffness was discussed. This data was then used to apply to a case study a simplified approach for the explicit introduction of uncertainty in a seismic assessment of a stone masonry building. The method was compared to established approaches of similar complexity and a reference Monte Carlo simulation. From the analysis, the relative impact of all sources of uncertainty on the total model uncertainty could be evaluated, showing the major relevance of the displacement capacity in determining the seismic performance. Secondly, a formulation of a macro-element model for the simulation of the in-plane and out-of-plane response of masonry walls is proposed. Its use in simulating from small element tests to shaking table tests on entire buildings is shown. The proposed macro-element is able to describe the out-of-plane dynamic response of buildings, showing the major sources of vulnerability and simulating the effect of the quality of connections on the global response, both in terms of displacement demands and failure modes.

EPFL2019

Numerical Simulation of Unreinforced Masonry Buildings with Timber Diaphragms

Katrin Beyer, Ivana Bozulic, Igor Tomic, Francesco Vanin

Though flexible diaphragms play a role in the seismic behaviour of unreinforced masonry buildings, the effect of the connections between floors and walls is rarely discussed or explicitly modelled when simulating the response of such buildings. These flexible diaphragms are most commonly timber floors made of planks and beams, which are supported on recesses in the masonry walls and can slide when the friction resistance is reached. Using equivalent frame models, we capture the effects of both the diaphragm stiffness and the finite strength of wall-to-diaphragm connections on the seismic behaviour of unreinforced masonry buildings. To do this, we use a newly developed macro-element able to simulate both in-plane and out-of-plane behaviour of the masonry walls and non-linear springs to simulate wall-to-wall and wall-to-diaphragm connections. As an unretrofitted case study, we model a building on a shake table, which developed large in-plane and out-of-plane displacements. We then simulate three retrofit interventions: Retrofitted diaphragms, connections, and diaphragms and connections. We show that strengthening the diaphragm alone is ineffective when the friction capacity of the wall-to-diaphragm connection is exceeded. This also means that modelling an unstrengthened wall-to-diaphragm connection as having infinite stiffness and strength leads to unrealistic box-type behaviour. This is particularly important if the equivalent frame model should capture both global in-plane and local out-of-plane failure modes.

2021

Equivalent frame models for in-plane and out-of-plane response of unreinforced masonry buildings

Francesco Vanin

EPFL2019