1,721,052 research outputs found
Le trasformazioni del paesaggio urbano di una colonia latina: il foro di Alba Fucens dalle fasi dell’impianto alle ultime frequentazioni
No full textPre- and post-simulations of shake-table tests on a stone masonry building aggregate using finite-discrete elements
Full text linkThis work presents the simulations of the non-linear dynamic response of a three-dimensional finite-discrete element model. The model simulates a half-scale masonry building aggregate tested on a shake table by other Authors. The aggregate is made of two un-connected building units having different heights and slightly different wall thicknesses. The floors are made of timber beams and boards. The modelling approach accounts jointly for in-plane and out-of-plane responses, which can be expected given the high flexibility of the floors, and for the separation between the two building units. The simulations are related both to the blind predictions, according to a scheduled testing sequence, and to the post-dictions according to the actual testing sequence and some model calibrations. The prediction model overestimates displacements, underestimates base shear and fairly predicts the damage pattern of comparable experimental runs. The use of the recorded shake table motion improves the accuracy of the post-diction simulations, while still delivering beam unseating. A higher Young’s modulus of the blocks improves markedly the predictions. The strengthening intervention with steel angles connecting floors to walls is only approximately modelled and does not improve the outcomes of the simulations. In summary, the adopted modelling approach is capable of accounting for the pounding between the two building units, predicting the most significant damage as well as estimating approximate average of peak values of base shear and displacements, while individual time histories are less accurately estimated
The Effect of the Vertical Component of Ground Motion on a Masonry Cross Vault Model
No full textRecent earthquakes have emphasized the high vulnerability of vaulted structures. Their collapse may entail only local damage or can affect the surrounding building because of its heavy mass and the significant horizontal thrust on supporting elements. In this paper, the influence of the vertical component of ground motion on the performance of a numerical model of an unreinforced masonry cross vault is investigated using sets of one-component and two-component ground motions to perform nonlinear dynamic analyses. The set of motions represents the actual seismicity of L’Aquila, Italy, while the investigated vault mimics a reference brickwork specimen. The numerical model falls within the mixed finite–discrete element method and accounts for crack formation, complete separation and new contact formation. The modelling strategy is capable to evaluate the ultimate displacement and load-bearing capacity of the vault under seismic loading and the progressive deformation of the vault up to collapse. The vault is excited by a horizontal component alone or by both horizontal and vertical components. Although without a systematic trend, adding the vertical component worsens the response in about 10% of cases
Combined Finite-Discrete Element Model Simulations of Shake-Table Tests on a Full-Scale Masonry Cross Vault
No full textThis work presents the numerical simulations of shaking table tests of a full-scale masonry cross vault. The boundary conditions simulate the presence of a continuous lateral wall and of a colonnade-between-naves condition. The seismic action is applied along the longitudinal direction of the specimen, with increasing amplitude. The model used for the simulations allows for the elastic finite element modelling of masonry units and the discrete element modelling of the interfaces between them. A tension cut-off governs the interface: no tensile stress can be transmitted once this strength is exceeded. The shear response is defined by cohesion and friction: once the former is exceeded the interface reacts according to Coulomb’s behaviour. The simulations are related to the blind predictions, according to the scheduled tests, and the post-dictions, according to the actual testing sequence. The prediction model overestimates displacements and does not catch the actual crack distribution. Therefore, a post-simulation model was implemented, revising the masonry elastic modulus as well as the stiffness and boundary conditions of the supporting piers. Simulations are improved both in terms of displacement predictions and damage mechanism. Finally, the sensitivity to finite-element size, damping ratio and block discretisation was explored
Hysteretic models with damage and flexibility increase
No full textThe need to accurately describe nonlinear degrading phenomena in both modern and classical complex materials that exhibit hysteretic behavior is a relevant task for the analysis of their response. In the present study an enrichment to an existing formulation to describe strength and stiffness degradation is proposed. The description of damage, that reduces the hysteretic force, is then accompanied by the introduction of flexibility increase, which increments the elastic displacement experienced by the system. Both effects influence the energy dissipated by the system. The condition of thermodynamic admissibility in presence of damage and flexibility increase is derived, entailing constraints on system parameters. Additional constraints arise from consistency conditions on the transformation of the pure hysteretic system into the system with damage and flexibility increase. A numerical solution involving the forward Euler method is presented to evaluate the response quantities. The formulation is eventually applied to the elastic–plastic and Bouc Wen hysteresis models, and the influence of the degrading parameters is presented. The presented Bouc-Wen model with damage and flexibility increase is applied to study the cyclic response of a masonry panel experimentally tested to validate the numerical model and prove its capability of describing the structural response
Equivalent frame modelling of masonry walls based on plasticity and damage
No full textThis paper presents a force-based equivalent frame procedure applied to analyse masonry walls structural response under cyclic loadings. The presented macroelement formulation, consisting in the arrangement in series of a central elastic beam, two nonlinear flexural hinges at the ends and a nonlinear shear link, adopts a smooth hysteresis model for these latter, where a scalar damage variable is introduced to reproduce strength and stiffness degradation. Main points of the adopted force-based macroelement and hysteresis model are recalled, with emphasis on the capability to reproduce the typical in-plane cyclic response of masonry. Validation of the element is presented through various examples, comparing numerical and experimental results. The first validation set is composed by a group of four panels, characterized by different boundary conditions and pre-compression levels. The second validation case is a classical literature benchmark, in which the performance of the model is tested in case of a wall with openings composed of piers, spandrels and rigid links. Moreover, for this example, numerical results obtained with the presented equivalent frame approach are also compared with a more refined numerical model, showing limits and advantages of simplified procedures
An enriched Bouc-Wen model with damage
No full textThis paper presents an enriched hysteresis model with damage relying on the Bouc-Wen formulation, in which a single scalar variable is introduced to reproduce effects of strength and stiffness degradation emerging for damaging materials. First, some acknowledged limits of the original Bouc-Wen model are discussed, focusing on its thermodynamic admissibility and compatibility with Drucker's plasticity postulate, and highlighting the effects of the parameters β and γ. Then, a reformulated expression of the dissipated energy is presented, which is consistent from the thermodynamic point of view. This formulation is extended to the case of degrading Bouc-Wen models. Uniaxial validation analyses are proposed, together with some considerations on the physical and thermodynamic admissibility of the model. The effect of pinching is also introduced by means of the arrangement in parallel of a non-dissipative Bouc-Wen and a degrading (damaging)device, resulting in a varied set of hysteresis shapes. Finally, the proposed model is adopted to analyse the cyclic response of masonry structural elements under in-plane horizontal loads. Within the framework of equivalent frame formulation, masonry panels are modelled by an elastic beam arranged in series with nonlinear flexural hinges lumped at the ends and a shear link, whose constitutive relationships are described by means of the enriched hysteretic model with damage
Modeling of Masonry Bridges in Presence of Damage: The Case Study of San Marcello Pistoiese Bridge
No full textSafeguard of the heritage of masonry infrastructural constructions is a relevant concern nowadays. The historical-monumental value of a large part of these artifacts, combined with their current functional reuse in the transport net-works, make them interesting case studies. These structures are generally afflicted by structural weaknesses that make them vulnerable under dynamic actions, strongly present in the Italian peninsula, due to its widespread and high seismicity. In this framework, Finite Element analysis turns out to be a useful tool to better understand the structural behavior of masonry artifacts. In this paper, the seismic assessment of a masonry arch bridge, located in Italy, is proposed by means of a 3D FE modeling. The masonry material is described through the adoption of a constitutive law with damage, capable of capturing the degrading behavior of masonry under cyclic actions, characterized by a strain softening response. The phenomenological law is characterized by the presence of a scalar damage vari-able, describing the material degradation evolving during the analysis. After the investigation of modal shapes of the bridge, the horizontal capacity curve was estimated through a pushover analysis, and finally the structure was subjected to a set of natural accelerograms. The health state of the case study was consequently defined by means of damage indexes, and the most critical areas of the bridge were highlighted through the study of the damage patterns
Damaging behavior of masonry arch bridges: analysis of 'Ponte delle Torri' in Spoleto, Italy
Full text linkDamage effects on the dynamic response of the masonry bridge 'Ponte delle Torri' in Spoleto are investigated. To model ancient masonry material response, a scalar damage variable is introduced in the stress-strain law, whose evolution is driven by a nonlocal strain measure. A 3D finite element formulation is used. Bridge natural frequencies and modal shapes are evaluated and compared with experimental results. Then, the nonlinear step-by-step dynamic analysis of the entire bridge and an equivalent pier is performed, considering a set of natural earthquakes. The response of the bridge is analyzed in terms of top displacement, acceleration and damage patterns
Development of parametric seismic fragility curves for historical churches
Full text linkFor both spiritual and cultural reasons, churches are an essential part of the historical heritage of several countries worldwide, including Europe, Americas and Australasia. The extreme damage that occurred during the 2016–2017 Central Italy seismic swarm highlighted once again the noteworthy seismic vulnerability of unreinforced masonry churches, which exhibited several collapses and caused uncountable losses to the Italian artistic heritage. The seismic performance of 158 affected buildings was analyzed in the aftermath of the main shocks. The failure modes activated by the earthquakes were identified making reference to the local mechanisms currently considered in Italy for post-seismic assessment of churches. The structural damage of the investigated buildings, related to 21 mechanisms rather than to an overall global response, was explained resorting to empirical statistical procedures taking into account ground motion intensity and structural details that can worsen or improve the seismic performance. Finally, parametric fragility curves were derived selecting those structural details that mostly influence the damage by means of the likelihood-ratio test. Developed models can be used in future territorial-scale scenario or risk analyses
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