Low unit strength masonry: computational modelling approaches

Masonry is characterized by the large variability of its components. Parameters like strength, bond and workmanship defects strongly influence the performance of the overall structure. The applicability of different computational modelling approaches to assess the structural behaviour of masonry has been studied. Two of the most relevant computational modelling approaches have been considered namely: finite element method (FEM) and distinct element method (DEM). In order to validate the numerical outcomes, comparisons with the experimental results have been undertaken. The aim of this paper is to contribute to the knowledge and selection of a suitable modelling approach for modelling low unit strength masonry structures. The results showed that in the case of low unit strength masonry, FEM is a more suitable approach to use. In fact, since in the considered case, the block is the weak component, it is not possible to assume the brick units as a rigid block. Therefore an accurate plasticity and cracking model for the brick is required

Repair of composite-to-masonry bond using flexible matrix

The paper presents an experimental investigation on an innovative repair method, in which composite reinforcements, after debonding, are re-bonded to the substrate using a highly deformable polymer. In order to assess the effectiveness of this solution, shear bond tests were carried out on brick and masonry substrates within two Round Robin Test series organized within the RILEM TC 250-CSM: Composites for Sustainable strengthening of Masonry. Five laboratories from Italy, Poland and Portugal were involved. The shear bond performance of the reinforcement systems before and after repair were compared in terms of ultimate loads, load-displacement curves and strain distributions. The results showed that the proposed repair method may provide higher strength and ductility than stiff epoxy resins, making it an effective and cost efficient technique for several perspective structural applications

Shake-table testing of a stone masonry building aggregate: overview of blind prediction study

City centres of Europe are often composed of unreinforced masonry structural aggregates, whose seismic response is challenging to predict. To advance the state of the art on the seismic response of these aggregates, the Adjacent Interacting Masonry Structures (AIMS) subproject from Horizon 2020 project Seismology and Earthquake Engineering Research Infrastructure Alliance for Europe (SERA) provides shake-table test data of a two-unit, double-leaf stone masonry aggregate subjected to two horizontal components of dynamic excitation. A blind prediction was organized with participants from academia and industry to test modelling approaches and assumptions and to learn about the extent of uncertainty in modelling for such masonry aggregates. The participants were provided with the full set of material and geometrical data, construction details and original seismic input and asked to predict prior to the test the expected seismic response in terms of damage mechanisms, base-shear forces, and roof displacements. The modelling approaches used differ significantly in the level of detail and the modelling assumptions. This paper provides an overview of the adopted modelling approaches and their subsequent predictions. It further discusses the range of assumptions made when modelling masonry walls, floors and connections, and aims at discovering how the common solutions regarding modelling masonry in general, and masonry aggregates in particular, affect the results. The results are evaluated both in terms of damage mechanisms, base shear forces, displacements and interface openings in both directions, and then compared with the experimental results. The modelling approaches featuring Discrete Element Method (DEM) led to the best predictions in terms of displacements, while a submission using rigid block limit analysis led to the best prediction in terms of damage mechanisms. Large coefficients of variation of predicted displacements and general underestimation of displacements in comparison with experimental results, except for DEM models, highlight the need for further consensus building on suitable modelling assumptions for such masonry aggregates

Evaluation of different computational modelling strategies for the analysis of low strength masonry structures

Masonry is a composite material characterized by a large variability of its constituent materials. The materials used, the quality of the bond and variations in the standard of workmanship significantly affect the mechanical performance of the overall masonry structure. Masonry structures, especially the historical ones, are usually characterized by low strength, due to a variety of reasons, namely low units and/or mortar strength or low bond; this makes more difficult to study these types of structures according to general rules because of different structural schemes. The aim of this paper is to evaluate the suitability of continuous FEM (Finite Element Method) or discrete DEM (Distinct Element Method) approaches to analyse the behaviour of low strength masonry and to contribute to the knowledge and selection of the best approach with a cost and time effective solution. The comparison with experimental results on different low strength masonry validated the approaches and showed that, for low bond strength masonry, DEM approaches performed better compared to low unit strength masonry where the emphasis on joint behaviour in DEM approaches is less effective because the weak component is the unit

Bending and buckling of timoshenko nano-beams in stress-driven approach

A modified total potential energy functional is derived for stress-driven non-local model of Timoshenko beam subject to transverse load and/or critical axial load. The modified functional includes expressions representing the constitutive boundary conditions, which are a peculiarity of the adopted stress-driven approach. The Euler equations of the modified functional are the governing equations of the stress-driven non-local model. Instead of solving directly the Euler equations, approximate solutions are searched by imposing the stationary condition of the modified functional through the Ritz method. In order to validate the method, the proposed numerical solutions are compared with closed-form expressions, in load cases where closed-form solutions are available. Finally, the proposed numerical method is used for determining the buckling load of non-local Timoshenko beam