1,720,976 research outputs found
Discrete rotating links model for the nonlinear torsion-shear behaviour of masonry joints
No full textThe numerical modelling of the torsion behaviour of masonry block interfaces is a key aspect for the assessment of the out-of-plane response of masonry walls. Nevertheless, it still represents a challenging computational issue due to the high non-linear coupling between the torsion and other internal forces (shear, bending moment and axial load), which rigorously requires the adoption of complex 3D non-linear constitutive laws. Some limit analysis-based approaches, proposed in the specific literature, represent efficient and reliable numerical tools for predicting the ultimate states of brick masonry structures subjected to combined in-plane and out-of-plane actions, while involving complex torsion loads and combined actions. This paper originally introduces a simplified discrete inelastic interface able to simulate the non-linear torsion-shear behaviour of masonry contact joints, within the context of static incremental analysis. The more general mechanical behaviour of the interface is ruled by six degrees of freedom and is governed by four rotating links (RL), whose actual orientation is updated during the step by step analysis, by taking into account the current position of the twisting centre of the interface. The incremental torsion-shear capacity curve and the corresponding ultimate domains obtained by the proposed model are compared with the ultimate load limit analysis predictions and with some experimental data available in the literature. The results highlight the ability of the new discrete interface to effectively reproduce the full non-linear behaviour of masonry contact interface subjected to different loading combinations
Discrete macro - models of nonlinear interlocking mechanisms in the out-of-plane failure of masonry walls
No full textHistorical unreinforced masonry (URM) constructions are generally vulnerable to out-of-plane (OOP) failures due to the absence of rigid floors and poor connections between orthogonal walls. That leads to the activation of rocking mechanisms of external walls, whose ultimate force and displacement are affected by complex nonlinear interactions with sidewalls. These interactions are often neglected in the engineering practice, potentially leading to significant approximations, as demonstrated by experimental and numerical studies available in the literature. As a novel contribution to the field, this paper presents an upgraded discrete macro-element model (DMEM) to predict the rocking capacity of OOP loaded URM walls interacting with sidewalls. Considering both the onset and the evolution of the rocking mechanism of the front wall, interlocking effects with the sidewalls are first simulated through frictional resistances using the macro-block model (MBM) and the nonlinear kinematic approach of limit analysis. Then, the upgraded DMEM is implemented on the basis of the equivalence between the continuous distribution of these forces, introduced as a further novelty of the paper, and the discrete distribution of lateral elastic-plastic links, accounting for mechanical and geometrical nonlinearities. The results of the two models are discussed in terms of both frictional resistance-displacement and pushover curves, referring to a case study of a front wall belonging to a two-storey URM building. The wall response is also compared with the results derived from the original source of the case study and analysed by changing the number of nonlinear links to define different levels of accuracy
A macro-modelling approach for arches strengthened with externally bonded inorganic matrix composites
No full textThe use of externally bonded inorganic matrix composites is becoming a common technique for strengthening arches and vaults to improve the load-carrying capacity with respect to both static and seismic loads. Experimental evidence has shown a complex behaviour where failure may occur within the reinforcement matrix, with a strong coupling between pure opening mode (mode I) and shear mode (mode II), as a consequence of the curvature of the substrate. Aiming at providing a tool for simulating the structural behavior of masonry arches reinforced with inorganic matrix composites, a discrete macro-modeling approach is proposed in which the reinforcement is described by means of piecewise rigid plates, which interact with the masonry through zero-thickness nonlinear interfaces. A refined bond constitutive law, specifically conceived to account for both the cohesive and the frictional contributions, as well as the coupling between mode I and mode II, in terms of strength and softening behavior, is proposed and implemented in a macro-elements model. The proposed model is then validated through comparison with analytical predictions and experimental direct shear tests performed with straight and curved substrates. Eventually, the model is used to reproduce the behaviour of a barrel vault strengthened with steel reinforced grout and tested up to failure
A hybrid macro-modelling strategy with multi-objective calibration for accurate simulation of multi-ring masonry arches and bridges
No full textThis paper presents an efficient hybrid continuum-discrete macro-modelling strategy with an enhanced multiscale calibration procedure for realistic simulations of brick/block-masonry bridges. The response of these structures is affected by the intrinsic nonlinearity of the masonry material, which in turn depends upon the mechanical properties of units and mortar joints and the bond characteristics. Finite element approaches based upon homogenised representations are widely employed to assess the nonlinear behaviour up to collapse, as they are generally associated with a limited computational demand. However, such models require an accurate calibration of model material parameters to properly allow for masonry bond. According to the proposed approach, the macroscale material parameters are determined by an advanced multi-objective strategy with genetic algorithms from the results of mesoscale “virtual” tests through the minimisation of appropriate functionals of the scale transition error. The developed continuum-discrete finite element macroscale description and the calibration procedure are applied to simulate the nonlinear behaviour up to collapse of multi-ring arch-bridge specimens focusing on the 2D planar response. The results obtained are compared to those achieved using detailed mesoscale models confirming the effectiveness and accuracy of the proposed approach for realistic nonlinear simulations of masonry arch bridges
Modelling the nonlinear static response of a 2-storey URM benchmark case study: comparison among different modelling strategies using two- and three-dimensional elements
Full text linkThis paper aims at comparing the use of different software environments for the study of a simple unreinforced masonry building through nonlinear static analyses. The presented results are part of a wider research project conducted within the ReLUIS consortium, and specifically within a research task whose purpose is providing practitioners with results and tools for an aware employment of commercial software packages for modelling masonry structures. In this study one of the benchmark structures of the research program is analysed; a two-story building characterized by rigid horizontal diaphragms, considering different configurations in terms of openings arrangements and effectiveness of ring beams, is subjected to seismic load conditions. Software packages considering two- and three- dimensional structural models are employed, and the obtained results are compared in terms of capacity curves and collapse mechanisms. One of the critical aspects on the basic assumptions made by software in terms of way to apply the horizontal loads is further investigated. In addition, the role of the shear strength is analysed correlating the mechanical properties to be adopted with micro- and macro- models. The considered models present very different features, and the analogies and differences obtained in the results are critically interpreted in view of the different hypotheses made by the software tools in terms of modelling strategies and adopted constitutive laws
OUT-OF-PLANE RESPONSE OF MASONRY CHURCH FACADES INCLUDING P-DELTA EFFECTS
No full textOut-of-plane rocking mechanisms represent one of the major causes of damage and failure for unreinforced masonry buildings, monuments and churches leading to significant economic and social losses every year in many regions throughout the world. Due to their slenderness, masonry walls subjected to rocking mechanisms can show large displacements before the complete overturning. Therefore, seismic analyses should consider geometrical nonlinearities, requiring more complex formulations and increasing the computational effort.
This paper applies a recently proposed P-Delta formulation of the discrete macro-element method (DMEM) to analyse the seismic behaviour of masonry façades interacting with lateral walls. The model accounts for geometrical nonlinearities considering the P-Delta effects by updating the load vector at each step of the analysis, avoiding assembling and updating the geometrical stiffness of the system. In addition, the capability of the model to describe the coupled in-plane and out-of-plane wall responses allows for describing spatial failure mech-anisms. The presented study aims at quantifying the role of the P-Delta effects in conjunction with the cohesive-friction connections between the façade and lateral walls on the ultimate rocking of the external façade. These effects are here investigated through pushover analyses on a church façade. The analyses are conducted on a global model, accounting for brick interlocking, and on a simplified model, including only the façade where ad hoc calibrated non-linear links simulate the interaction with the lateral walls. The results show that geometrical nonlinearities affect the façade’s response even at relatively low-magnitude displacements, with increasing influence as the quality of the façade-to-lateral-walls connections reduces
A DISCRETE-MACRO-ELEMENT-MODEL FOR THE IN-PLANE ANALYSIS OF MASONRY STRUCTURES STRENGTHENED BY FRCMS
Full text linkRecent earthquakes demonstrated the vulnerability of existing and historical masonry constructions. Many strengthening techniques for the seismic retrofitting of these structures have been introduced in the literature. Among these, FRCM strategies, based on the application of fibrereinforced composite materials on the masonry surface through inorganic mortar layers, has become rather popular due to their physic and mechanic compatibility with historical masonries, low invasiveness and capacity to improve both the in-plane and the out of plane masonry behaviour. In this paper, a simplified discrete model, working at the material macroscale, is proposed to simulate the in-plane behaviour of masonry panels strengthened by FRCM systems. The proposed modelling approach is based on the DMEM model, whose calibration is enhanced to encompass the properties of the externally bonded strengthening system. According to the proposed strategy, the masonry support and the FRCM layers are simulated by..
A comparative study on a complex URM building: part II—issues on modelling and seismic analysis through continuum and discrete-macroelement models
Full text linkThe paper presents the comparison of the results obtained on a masonry building by nonlinear static analysis using different software operating in the field of continuum and discrete-macroelement modeling. The structure is inspired by an actual building, the "P. Capuzi" school in Visso (Macerata, Italy), seriously damaged following the seismic events that affected Central Italy from August 2016 to January 2017. The activity described is part of a wider research program carried out by various units involved in the ReLUIS 2017/2108—Masonry Structures project and having as its object the analysis of benchmark structures for the evaluation of the reliability of software packages. The comparison of analysis was carried out in relation to: global parameters (concerning the dynamic properties, capacity curves and, equivalent bilinear curves), synthetic parameters of structural safety (such as, for example, the maximum acceleration compatible with the life safety limit state) and the response in terms of simulated damage. The results allow for some insights on the use of continuum and discrete-macroelement modeling, with respect to the dispersion of the results and on the potential repercussions in the professional field. This response was also analyzed considering different approaches for the application of loads
Targeted steel frames by means of innovative moment resisting connections
No full textThe present paper proposes the use of stepped cross section devices on steel frames aiming at reproducing a pre-established target push-over curve. To this aim a Limited Resistance Plastic Device (LRPD) to be inserted along selected structural members is proposed. The following two main specific features for LRPD are required: any elastic flexural stiffness variation of the original selected member must be avoided; an ultimate plastic bending moment value equal to an assigned percentage of the original limit resistance value must be ensured. Steel frames equipped with LRPD are modeled by means of an extension of a recently proposed Fibre Smart Displacement Based (FSDB) beam element model, characterized by the adoption of updating shape functions. The novelty of this research, with respect to previous studies, regards: i) the formulation of a targeted plane steel frame by means of a new optimal design procedure for the LRPD with assigned stiffness and resistance features, independent of each other; ii) the development of a FSDB beam element approach suitably devoted to such a special application of discontinuous cross sections devices. The design procedure and the FSDB model for the analysis of the real behaviour of the proposed LRPD device in the field of distributed plasticity is validated against detailed 3D finite element models
Smart beam element approach for lrph device
Full text linkLRPH (Limited Resistance Rigid Perfectly Plastic Hinge) device is a special steel device mainly usable to join beam elements of plane or spatial steel frames covered by patent n. 102017000088597 at the Italian Ministry of Economic Development and identified in the International Patent System with the number PCT/IB2018/055766. In the framework of moment (rigid) connection, the main fundamental innovation of LRPH consists in the mutual independence of its own resistance and stiffness features. The device is constituted by a sequence of three steel elements of limited length bounded by two parallel steel plates joined up with the connected structure elements. The cross-sections of the three steel elements are classical I sections with appropriate wing and web thicknesses obtained by the solution of suitable optimal design problem. Therefore, the overall device shows piecewise discrete geometric and mechanical features. In order to implement this device in a frame-oriented code for the design of both 2D and 3D frame structures, it is necessary to adopt a suitable model based on a non-uniform cross section beam element. The latter element should be able to reproduce the elastic and plastic behavior of the device. Recently, in the literature it has been proposed a new inelastic beam element, belonging to the displacement based approach and formulated for uniform beams, based on variable displacement shape functions, whose analytic expressions are prone to updating (smart) in accordance to the plastic deformation evolution in the beam element. Aim of the paper is to utilize the relevant smart displacement beam element approach and extend it to the case of non-uniform beams to evaluate the nonlinear behavior of the LRPH device. The obtained results confirm the efficacy and the feasibility of the smart displacement beam element opening the way of implementing LRPH device in a FEM code
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