1,721,013 research outputs found
MESO-STRUCTURAL MODELLING OF FIBRE REINFORCED CONCRETE
No full textIn this paper, the Lattice Discrete Particle Model (LDPM) is extended to include the effect of dispersed fibers with the objective of simulating the behavior of fiber reinforced concrete for armoring system applications. Within the LDPM framework, the effect of dispersed fibers is taken into account through the following procedure. 1) Fibers are randomly placed in the volume of interest according to the given fiber volume ratio and fiber geometry; 2) the number and orientation of fibers crossing each facet are computed along with the fiber embedment length on each side of the facet; 3) at the facet level, fibers and plain concrete are assumed to be coupled in parallel; 4) the contribution of each fiber to the facet response is formulated on the basis of a micromechanical model of fiber-matrix interaction. The developed model, named LDPM-F, is validated by carrying out numerical simulations of direct tension and three-point bending tests on fiber reinforced concrete mixes characterized by various fiber volume fractions. Finally, LDPM-F is applied to the analysis of the penetration resistance of fiber reinforced slabs
Simulating the Nonlinear Mechanical Behavior of FRCM-strengthened Irregular Stone Masonry Walls
No full textEarthquakes constitute a significant cause of degradation and damage for masonry heritages, such as churches, palaces, castles, and entirely historical centers. This work aims to investigate numerically the Fiber Reinforced Cementitious Matrix (FRCM) system applied as coating- reinforcement to existing stone masonry walls. Indeed, despite the FRCM is, nowadays, one of the most widely adopted systems for the consolidation of masonry structures, the knowledge on its mechanical behavior is still incomplete. In this work, diagonal compression tests performed on reinforced stone masonry panels are simulated and interpreted by adopting a sophisticated numerical framework, based on the Lattice Discrete Particle Model (LDPM), which simulates, at the length scales of the masonry stones and coating mortar grains, the fracture and failure behavior of the quasi-brittle heterogeneous materials by modeling the interaction among irregular particles. Different assumptions on the FRCM features (bond behavior and thickness of the coating mortar, and the presence or not of the fiber grid therein the coating mortar) were investigated to better understand their effect. The computational effort of using that method was rewarded from the possibility of capturing the main aspects of the material heterogeneity on the fracture propagation and damage evolution in the reinforced masonry walls
Lattice Discrete Particle Model for the Simulation of Irregular Stone Masonry
No full textThis paper focuses on the simulation of irregular stone masonry by the lattice discrete particle model (LDPM), which simulates the fracture and failure behavior of quasi-brittle heterogeneous materials by modeling the interaction among coarse material heterogeneities. LDPM is formulated at the length scale of the masonry stones whose interaction is described through constitutive equations featuring softening in tension and strain hardening in compression. The numerical results relevant to diagonal compression tests show that the intrinsic stochastic character of LDPM can quantify the variation of the mechanical properties of irregular masonry resulting from random stone size and stone-size distribution. Furthermore, the paper presents an analysis of the size effect on irregular stone masonry structures. This was obtained by simulating the shear behavior of geometrically similar samples of different sizes. The simulations demonstrate that increasing structural size leads to a significant reduction of both structural strength and structural ductility. The magnitude of the predicted size effect suggests that, contrary to typical experimental results on reduced size samples, real irregular masonry structures must be considered as perfectly brittle
Fiber Reinforced Cementitious Matrix (FRCM) for strengthening historical stone masonry structures: experiments and computations
No full textDiscussion of the article “On shear in members without stirrups and the application of energy-based methods in light of 30 years of test observations”
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Size Effect on Shear Strength of Reinforced Concrete: Is CSCT or MCFT a Viable Alternative to Energy-Based Design Code?
No full textAfter sketching the history of the size effect models for the shear strength of reinforced concrete (RC) in design codes, the energy-based size effect law (SEL), recently incorporated into the American Concrete Institute (ACI) design code articles for beam shear and slab punching, is briefly discussed. A general derivation of the SEL based only on the first principles involving energy conservation and dimensional analysis (or laws of similitude) is presented. Attention is then focused on recent articles that present a severe critique of the SEL and various arguments in support of the Muttoni et al.'s critical shear crack theory (CSCT)-an update of the Collins et al.'s modified compression field theory (MCFT)-that some researchers propose to be introduced into the fib Model Code and the Eurocode as an alternative to the SEL. In a point-by-point analysis, it is shown that this critique and these arguments are incorrect and baseless. It is hoped that the present clarification would lead to progress in design codes, enhancing the safety and efficiency of RC structures. (c) 2020 American Society of Civil Engineers
On the collapse of the masonry Medici tower: An integrated discrete-analytical approach
No full textMasonry towers are characterized by a high susceptibility to seismic actions. For this task different approaches exist and they are selected depending on the desired level of accuracy of the analysis. The identification of the correct collapse configuration is however complex and necessitates thorough on-site surveys. Construction codes usually require the study of local and global collapse mechanisms based on simplified kinematic analysis. More elaborated approaches such as nonlinear finite element methods have been used to simulate the response of masonry towers. Although successful in many applications, these methods are limited in accurately capturing crack distributions and fracture mechanisms. In this work, an integrated discrete-analytical approach is proposed. First, the Lattice Discrete Particle Model (LDPM), which simulates masonry at the stone level and has a superior capability in capturing fracturing processes, is adopted to simulate masonry towers subjected to seismic excitation. The numerical model is used to predict the actual collapse mechanism. Next, the final fractured configuration is used in the kinematic analysis for the calculation of the ultimate condition. The proposed method is used to analyze the collapse of the Medici tower that collapsed during the 2009 L'Aquila earthquake. The simulations are able to predict the induced damage and the crack contours, which are used then to identify six different failure configurations. The subsequent kinematic analyses take into account the relative position of openings and fracture locations. The results show that the collapse of the Medici tower is well replicated by LDPM and the corresponding kinematic analyses demonstrate the efficiency of the proposed hybrid approach applied to this case study. The paper also points out that different load configurations, more specifically the direction of the seismic action, result in certain cases in more diffused damage and a clear failure pattern cannot be identified for kinematic analyses. In these cases, it appears fundamental to rely mainly on comprehensive numerical models, such as LDPM, to study the fracturing process from the cracks trigger to the ultimate complex collapse mechanism
Discussion of the article "From experimental evidence to mechanical modeling and design expressions: The critical shear crack theory for shear design"
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Analysis of the behavior of the masonry Medici tower resorting on a hybrid discrete-kinematic methodology
Full text linkThis study presents a novel integrated discrete-analytical approach for analyzing the collapse behavior of the masonry Medici tower (L'Aquila, Italy). Due to their slenderness, masonry towers are characterized by high susceptibility to seismic actions and several approaches can be adopted to analyze their seismic vulnerability. Generally, engineers -practitioners and researchers study the local and global collapse mechanisms based on simplified kinematic analysis, as prescribed by national and international construction codes or, alternatively, more sophisticated approaches such as nonlinear finite element methods have been adopted to simulate the response of masonry towers. Although successful in some applications, these methods are limited in accurately capturing crack distributions and fracture mechanisms. In fact, they completely ignore the damage propagation phenomenon, starting from the trigger of the fracture up to the complete structural failure condition, that is instead fundamental aiming to analyze intermediate damage states for the check of serviceability limit states or to individuate a more realistic structural crack distribution in ultimate conditions. This work proposes a hybrid discrete-kinematic approach: first, the Lattice Discrete Particle Model (LDPM), that simulates masonry at meso-scale, is used to individuate the actual collapse mechanism; next, the individuated cracked configuration is used in the kinematic analysis for the analysis in ultimate conditions. The results show that the collapse of the Medici tower due to the 2009 L'Aquila earthquake is well predicted by LDPM and the corresponding limit analyses demonstrate the efficiency of the proposed hybrid approach applied to this case study. Additional results point out that different load configurations, more specifically variations in the direction of the seismic action, provoke in certain cases a more diffused damage and a clear failure pattern can not be identified for kinematic analyses. In these cases, relying mainly on comprehensive numerical models, such as LDPM, is fundamental to study the fracturing process from the cracks trigger up to the ultimate complex collapse mechanism. (C) 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0
Fracturing and collapse behavior of masonry vaulted structures: a lattice-discrete approach
No full textThis study presents a novel meso-scale approach to investigate the fracturing and collapse behaviors of unreinforced masonry vaulted structures induced by spreading supports. Traditionally, the behavior of masonry vaulted structures is investigated by resorting on limit analysis method, that is a limited approach as: (i) it tackles just the failure condition of the arched structural configuration as it assumes the simultaneous formation of hinges once the thrust line reaches the edge of the masonry structure, (ii) it completely ignores the damage propagation phenomenon, starting from the trigger of the first fracture up to the complete structural failure condition. The comprehension of this fracturing process is fundamental aiming to analyze intermediate damage states for the check of serviceability limit states and to individuate a more realistic structural crack distribution in ultimate conditions. This paper proposes a thorough understanding of the fracturing behavior of masonry vaults based on non-linear fracture mechanics concepts. For this purpose, the Lattice Discrete Particle Model (LDPM) is adopted to simulate a variety of stone masonry vaulted structures up to their collapse. LDPM simulates the behavior of masonry at the stone level. The interaction between stones that are bounded by weak layers of mortar is governed by specific constitutive equations describing tensile fracturing with strain-softening, cohesive and frictional shearing, and compressive response with strain-hardening. The formation of hinges, the activation of the mechanism and the kinematic mechanism are analyzed for three different types of vaults, namely groin, barrel and depressed vaults, and for six different slenderness. The first conclusion of this study is that LDPM can be used as an alternative tool to perform typical limit analysis for the assessment of safety of arches and vaults in ultimate conditions. Most importantly, LDPM is able to show that the fracturing process is a progressive phenomenon, the cracked surfaces are never strictly symmetric respect to the vertical axis and do not appear simultaneously. In particular, the features of non simultaneity and asymmetry of the cracks increases as the distance between the crown of the vault and the imposts increases, i.e. going from depressed vaults to groin vaults. Finally, the evolution of the fracturing process occurs more progressively and exhibits less pronounced asymmetry in the case of depressed vaults as compared to groin vaults for which, in turn, the damage appears to be more brittle and characterized by asymmetry in the cracks distribution
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