1,721,804 research outputs found
A Reissner–Mindlin limit analysis model for out-of-plane loaded running bond masonry walls
No full textEarthquake surveys have demonstrated that the lack of out-of-plane strength is a primary cause of failure in many traditional forms of masonry. Moreover, bearing walls are relatively thick and, as a matter of fact, many codes of practice impose a minimal slenderness for them, as for instance the recent Italian O.P.C.M. 3431 [2005. Ulteriori modifiche ed integrazioni all’OPCM 3274/03 (in Italian) and O.P.C.M. 3274, 20/03/2003, Primi elementi in materia di criteri generali per la classificazione sismica del territorio nazionale e di normative tecniche per le costruzioni in zona sismica (in Italian)], in which the upper bound slenderness is fixed respectively equal to 12 for artificial bricks and 10 for natural blocks masonry. In this context, a formulation at failure for regular assemblages of bricks based both on homogenization and Reissner–Mindlin theory seems particularly attractive. In this paper a kinematic limit analysis approach under the hypotheses of the thick plate theory is developed for the derivation of the macroscopic failure surfaces of masonry out-of-plane loaded. The behavior of a 3D system of blocks connected by interfaces is identified with a 2D Reissner–Mindlin plate. Infinitely resistant blocks connected by interfaces (joints) with a Mohr–Coulomb failure criterion with tension cut-off and compressive cap are considered. Finally, an associated flow rule for joints is adopted. In this way, the macroscopic masonry failure surface is obtained as a function of the macroscopic bending moments, torsional moments and shear forces by means of a linear programming problem in which the internal power dissipated is minimized, once that a subclass of possible deformation modes is a priori chosen. Several examples of technical relevance are presented and comparisons with previously developed Kirchhoff–Love static [Milani, G., Lourenc ̧o, P.B., Tralli, A., 2006b. A homogenization approach for the limit analysis of out-of-plane loaded masonry walls. J. Struct. Eng. ASCE (in press)] and kinematic [Sab, K., 2003.Yield design of thin periodic plates by a homogenisation technique and an application to masonry walls. C.R. Mech. 331, 641–646] failure surfaces are provided. Finally, two meaningful structural examples are reported, the first concerning a masonry wall under cylindrical flexion, the second consisting of a rectangular plate with a central opening out-of-plane loaded. For both cases, the influence of the shear strength on the collapse load is estimated
Closed form solutions in limit analysis for masonry cloister vaults and domes subjected to concentrated vertical loads applied at the top crown
No full textTwo cases technically relevant are investigated in the field of the prediction of the load carrying capacity of masonry double curvature structural elements, namely hemispherical domes and square cloister vaults subjected to concentrated vertical loads at the top crown. Such loading condition is encountered quite frequently in practice, for instance for domes with lanterns and for cloister vaults belonging to historical buildings loaded in the middle span. A failure mechanism is hypothesised and analytical expressions for the different contributions in the internal and external power dissipation are deduced. The collapse multiplier is then obtained through the application of the principle of virtual powers. The advantage stands in the applicability of the method for a large variety of domes and cloister vaults (with a generalisation to additional special conditions, such as for instance in case of elliptic and rectangular in-plane geometries, presence of oculi and so on). The approach proposed is benchmarked on two case-studies experimentally tested, for which several numerical results coming from different models are already available
Guest editorial for the special issue of selected and extended papers presented at the 10th International Masonry Conference
No full textThis special issue presents a selection of extended and thoroughly revised papers resulting from the 10th (IMC) International Masonry Conference, which took place at the Technical University of Milan (Politecnico di Milano) in Milan, Italy from 9 to 11 July 2019
Simple model with in-parallel elasto-fragile trusses to characterize debonding on FRP-reinforced flat substrates
No full textIn many structural applications for masonry and rc strengthening, Fiber Reinforced Polymer (FRP) composites exhibit a typical mode II fracture behavior at the bond between substrate and strip when the latter is subjected to considerable tensile stresses. At structural level, the debonding mechanism is usually considered lumping the non-linearity at the interface. A variety of different models is already available to accurately study the debonding, but their utilization within a standard low-cost FE software is difficult, because of the limited gallery of nonlinear elements at disposal for the user. Among the most common elements available, the simplest one is the so-called cutoff bar, which is a truss behaving in an elastic-perfectly brittle way. The paper presents a recursive analytical approach to study debonding using a device constituted by several in-parallel cutoff bars. To closely fit existing analytical models’ response, it is shown that many in-series cutoff bars should be used. Due to the considerable number of elements required, such procedure is still hardily implementable, albeit theoretically applicable. For this reason, an identification procedure of a layer of trusses representing FRP and connected to the support with a layer constituted by two in-parallel cutoff bars is proposed. To do so, the selection of only two target points located on the actual global debonding curve is needed. Resultant mechanical properties of the cutoff bars allow to fit very closely the global behavior obtained through analytical approaches with an extremely simple discretization. The model is successfully validated against an already presented closed form procedure and applied on a set of experimental data available in the literature
Preface: Themed Issue on: Masonry Research in the Third Millennium: From Theory to Practical Applications
No full textIJMRI proposes and fosters discussion on the mechanics of masonry structures, with emphasis on a variety of topics including theoretical investigations, numerical approaches and technical applications in new works, repair practice and built heritage preservation. This perspective acknowledges the complexity of the masonry research sector, bridging between theory and application, with a readership spanning across from academia to industry
Fast Vulnerability Evaluation of Masonry Towers by Means of an Interactive and Adaptive 3D Kinematic Limit Analysis with Pre-assigned Failure Mechanisms
No full textThe paper presents an interactive kinematic limit analysis approach that can be handled also by inexperienced users for a reliable evaluation of the seismic vulnerability of masonry towers. The procedure requires only a 3D Computer-Aided Design CAD representation of the tower and the mechanical properties to assign to the different volumes. Five possible failure mechanisms are hypothesized, corresponding to those more frequently observed during post-earthquake surveys. They are all constituted by few macro-blocks mutually roto-translating and the code proposed automatically optimizes the shape of the selected failure mechanisms with a Genetic Algorithm GA approach, minimizing the failure multiplier—in agreement with the upper bound theorem of limit analysis—so furnishing quickly an estimation of the collapse acceleration and the crack pattern at collapse. The approach has several advantages, the most important being (1) the possibility to account for the actual geometry of the tower in an extremely detailed manner (so considering openings, irregularities, mass variation along the height, etc.), (2) the drastically reduced computational burden needed (only the recursive evaluation of the principle of virtual powers is required), (3) the adaptation of the failure mechanisms to the specificity of the problem treated, (4) the possibility to apply distributions of horizontal loads different from standard ones and finally (5) the possibility of utilization for all those practitioners not familiar with finite elements and computational limit analysis. The practical procedure proposed is validated against FE pushover computations and non-linear dynamic analyses conducted on two historical towers located in northern Italy, showing perfect agreement with results obtainable by means of complex procedures certainly not manageable at a common professional level
Cittadinanza e separatismi. Esperienze e prospettive in Europa. Atti del Convegno Università degli Studi di Siena, 8 aprile 2022
No full textThe book collects the papers presented at the Conference held in Siena on 8 April 2022 as part of the PRIN 2017 project "Constitutional implications of European separatisms", Research Unit of the University of Siena "Separatisms, minority rights and transformations of citizenship". The purpose of the meeting and of this publication is to reflect on a theme that, in the context of legal studies on separatism, is not frequently addressed, namely the relationship between such phenomena and the rules of citizenship.Il volume raccoglie le relazioni presentate al Convegno realizzato a Siena l’8 aprile 2022 nell’ambito del progetto PRIN 2017 “Implicazioni costituzionali dei separatismi europei”, Unità di ricerca dell’Università di Siena “Separatismi, diritti delle minoranze e trasformazioni della cittadinanza”. Lo scopo dell’incontro e della presente pubblicazione è quello di riflettere su un tema che, nell’ambito degli studi giuridici sui separatismi, non è frequentemente oggetto di analisi, ovvero il rapporto tra siffatti fenomeni e la disciplina della cittadinanza
Simple lower bound limit analysis model for masonry double curvature structures
No full textA new Lower Bound LB plate and shell limit analysis Finite Element FE model for the analysis at collapse of masonry double curvature structures is presented. The discretization relies into hexahedrons assumed infinitely resistant and quadrilateral interfaces where all plastic dissipation occurs. On such interfaces, the flexural behavior is ruled by the interaction between bending moment and axial load, whereas the shear and torsional behavior are modeled by means of an in-plane tangential force, out-of-plane shear and a plate torque. The resultant limit analysis problem obtained by such a formulation is particularly straightforward and the number of variables to deal with very limited. Equilibrium is indeed imposed only on hexahedrons and admissibility on interfaces between adjoining elements. Masonry can be modeled obeying a classic no-tension material or with more complex linearized failure surfaces, for example derived from suitable homogenization techniques. A simple Linear Programming LP problem is so derived, where the actual thickness of the structure is accurately accounted for, a key feature to assess the stability of a vault in case of the no-tension material assumption. The numerical model is validated by means of several meaningful structural examples. A detailed comparison with numerical data available in the literature, obtained for the same examples with alternative numerical approaches shows the accuracy of the method proposed and its usefulness for a fast and reliable prediction of the load carrying capacity of masonry double curvature structures
Semi-analytical mechanical model for FRCM-to-substrate shear bond tests
Full text linkThe debonding process of an FRCM reinforcing system from the substrate is studied in a semi-analytical fashion. FRCM is modeled considering independently the central elastic fiber grid and the two thick upper and lower matrix layers, assumed elasto-fragile; matrix and fiber are considered in a monoaxial state of stress; they mutually exchange shear stresses at the interface, this latter characterized by a softening stress-slip relationship; the reinforcement system is then bonded with a rigid substrate by means of a further elastic interface. Under such hypotheses, a simple system of first order non-linear and coupled differential equations is derived and solved by means of a semi-analytical approach. Independent variables are the axial displacements of the three layers (upper and lower matrix, central fiber) and the corresponding axial stresses. The approach is successfully validated against two experimental datasets available in the literature, relying into different FRCM strengthening systems bonded to rigid substrates and subjected to single lap shear tests. The model is able to capture not only the global debonding behavior but also the local one, with a precise prediction along the bond length of the shape of the axial stresses into the different layers, of the interface shear stresses and of the location of the cracks inside the matrix
Vulnerability Evaluation of Historical Masonry Structures: Italian Churches and Towers
No full textThe evaluation of the seismic vulnerability for historical masonry structures like churches and towers (medieval defense towers, bell towers and city gates) is paramount for developed countries. This is particularly true for Italy, a high seismicity country where it is esteemed that more than 5% of the total architectural heritage is located (UNESCO source). Consistently with the need of a sound protection of such kind of structures against seismic events, specific Guidelines for the built heritage have been conceived, which provide useful hints to practitioners for an assessment, but still leave important open issues. The present paper reviews the existing numerical approaches used for churches and towers. For churches, a guidebook for a reliable evaluation of the seismic vulnerability is proposed, relying into a broad blend of different approaches ranging from the easiest ones –usually available to practitioners- to the most sophisticated, like for instance Non-Linear Dynamic Analyses with damaging materials. A simplified procedure of FE upper bound limit analysis with coarse mesh adaptation is finally reviewed, which is sufficiently simple for common use but at the same time allows a realistic prediction of the most vulnerable macro-elements and the collapse acceleration. For towers, a straightforward approach based on the vulnerability evaluation by means of five probable (observed) failure mechanisms is proposed to overcome the limitations of a too simplistic cantilever beam approximation and to avoid demanding non-linear computations with 3D FEs
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