1,720,973 research outputs found
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 textSimulating defects in brick masonry panels subjected to compressive loads
No full textAlthough widespread in civil engineering construction, brick masonry walls usually designed to resist only gravity loads are known to be vulnerable structural elements with respect to seismic loads. They are generally made of units (bricks, stones or concrete blocks) and mortar joints and are by definition non-homogeneous and composite structures. The mechanical behavior of brick masonry has been studied extensively in the past decades both experimentally and by means of numerical simulations, considering the complex interaction between units and the surrounding mortar. One major aspect of the structural vulnerability of masonry panels, not well explored in the current literature, is the presence of geometrical and material defects accidentally introduced within the masonry panel during the construction process. Accounting for these defects by performing experimental campaigns is very difficult under the point of view of the replicability and, also, it is a costly and time-consuming activity. This manuscript deals with the modeling of the compressive behavior of brick masonry panels accounting for the presence of geometrical and material defects. For this purpose, a micro-modeling approach is proposed where brick units, mortar joints, and unit-mortar interfaces are simulated explicitly and the nonlinear behavior of the constituent materials is taken into account. The model was first validated on a large set of experimental data by predicting the overall panels' elastic behavior and bearing capacity of four different types of brick wall geometries. Next, geometrical and material defects were introduced in the model including: (i) the absence or the ineffectiveness or vertical mortar joints, (ii) the variability in the thickness of horizontal mortar joints and (iii) the inherent random distribution of bricks and mortar mechanical properties. Numerical results show that the quality of vertical joints defects does not significantly affect the mechanical response of masonry panels in compression, whereas the horizontal mortar joint defects can reduce the masonry compressive strength up to about 35%. In terms of material defects, the variability in compressive strength of brick units alone was found not to alter the mechanical behavior of the panels. On the other hand, both the overall strength and ductility of the masonry walls are appreciably affected when a not uniform distribution of the material properties are considered simultaneously in brick units and mortar joints
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
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
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
Masonry vaulted structures under spreading supports: Analyses of fracturing behavior and size effect
No full textThis paper deals with the fracturing behavior of unreinforced masonry arches and vaults induced by spreading supports. The traditional method of limit analysis is limited in understanding the actual failure of arches, as it assumes the simultaneous formation of hinges once the thrust line reaches the edge of the masonry structure. The damage propagation phenomenon, starting from the trigger of the fracture up to the complete structural failure is thus ignored. Moreover, limit analysis does not capture the effect of structural size on the nominal strength due to strain-softening and damage localization. This manuscript proposes a thorough understanding of the fracturing behavior and size-effect of arches and vaults based on computational modeling and 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. 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 slendernesses. The effect of arch size on structural strength is then analyzed using LDPM, by simulating self-similar arches of five different sizes and of three different slenderness ratios. The numerical data of size-effect is also analyzed using a newly developed analytical formula based on non-linear fracture mechanics theory and taking into account self-weight, whose effect is of paramount importance in arches and vaults under spreading supports. Results show a strong reduction of structural strength as the size increases, as a matter of fact stronger than the typically observed reduction due to energetical size-effect. The difference is due to self-weight, one of the main driving forces in the collapse of thrusting arches. This might explain the reason why in some seismic locations, small sized vaulted structures remain almost undamaged whereas larger ones often collapse
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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