This work is dedicated to the assessment of the nonlinear behaviour of masonry panels with regular texture and subject to in-plane loads, by means of numerical pushover analysis and an analytical homogenized model. Two numerical models are considered and adopted for performing a set of numerical tests: a discrete model developed by authors and a discrete/finite element model frequently adopted in rock mechanics field and effectively extended to masonry structures. In both models the hypotheses of rigid blocks and elastic--plastic joints following a Mohr--Coulomb yield criterion are adopted. The aim of this work is twofold: (1) a comparison and a calibration of the numerical models, evaluating their effectiveness in determining ultimate loads and collapse mechanisms of masonry panels, by assuming a nonlinear homogenized model for regular masonry as reference solution; (2) the evaluation of sensitivity of masonry behaviour and numerical models to panel dimension ratio and to varying masonry texture. In a first case study, sliding collapse mechanisms changing to overturning collapse mechanisms for increasing panel and block height-to-width ratio are obtained and the results given by the numerical models turn out to be in good agreement. Furthermore, a second case study, dedicated to square panels supported at base ends and vertically loaded, shows different `arch mechanisms' depending on block height-to-width ratio
Earthquakes represent one of the major threats to cultural heritage monuments, such as classical ancient columns. Understanding the behaviour and dynamic response of such historic structures is useful for the assessment of the conservation and rehabilitation techniques to be used for their preservation. The behaviour of ancient multi-drum and monolithic columns subjected to dynamic loads is characterised by highly nonlinearity since both rocking and sliding phenomena can occur. Analytical studies of multi-drum columns subjected to dynamic load is extremely complicated, if not impossible to perform. Nowadays, computational methods of analysis can be used to represent their dynamic response. Using a software based on the Discrete Element Method (DEM) of analysis, a typical ancient multi-drum and an equivalent in dimensions monolithic columns subjected to horizontal and combined horizontal and vertical harmonic excitations were modelled to identify the main factors affecting their stability. Different acceleration amplitude and frequency input records were applied and their role in the collapse/deformation mechanism was investigated. From the results analyses it was shown that novel structural analysis tools that extend traditional methods of structural assessment could allow engineers to understand the mechanisms that have allowed the surviving structures to avoid structural collapse and destruction during strong earthquakes.
Making use of a mixed variational formulation based on the Green function of the substrate, which assumes as independent fields the structure displacements and the contact pressure, a simple and efficient Finite Element-Boundary Integral Equation (FE-BIE) coupling method is derived and applied to the stability analysis of beams and frames resting on an elastic half-plane. Slender Euler-Bernoulli beams with different combinations of end constraints are considered. The examples illustrate the convergence to the existing exact solutions and provide new estimates of the buckling loads for different boundary conditions. Finally, nonlinear incremental analyses of rectangular pipes with compressed columns and free or pinned foundation ends are performed, showing that pipes stiffer than the soil may exhibit snapthrough instability
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