4,829 research outputs found
"Mozambique. Lourenco Mutaca and Sarfu Khan Mohammed", 1965
No full text"Mozambique. Lourenco Mutaca and Sarfu Khan Mohammed" in Information bulletin v. 42 (1965 May 13): p. 54- . The article praises the fraternal atmosphere of the discussions during the first FRELIMO congress. It also mentions the founding date of FRELIMO; the material aid of African and Asian countries in their war against the Portuguese colonialists
Heterogeneous and homogenized FE models for the limit analysis of out-of-plane loaded masonry walls
No full textIn the present contribution, a full 3D heterogeneous and a 2D homogenized kinematic FE limit analysis approach are employed for the evaluation of collapse loads and failure mechanisms of both running and English bond masonry slabs simply supported at the edges and out-of-plane loaded. Information at failure given by the full 3D approach underlines that particular care should be used in the evaluation of collapse loads with 2D approaches in case of multi-wythes panels
Automatic mesh generator for the non-linear homogenized analysis of double curvature masonry structures
No full textAn automatic full 3D mesh generator for the non-linear 3D homogenized discrete FE analysis of masonry double curvature structures is presented. The method can reproduce the main features exhibited by masonry, preserving the orthotropy and accounting for the influence of membrane loads on the flexural behavior. Previous homogenization procedures allow reducing the number of variables, leading to non-linear analyses with a low computational burden. In the approach proposed, masonry is modeled through an assemblage of elastic cells joined by non-linear interfaces with finite thickness. The latter are modeled as brick elements with softening replicated by a damage constitutive relationship (known in Abaqus - the commercial FE code used - as Concrete Damage Plasticity). The discrete mesh is obtained automatically by means of an ad-hoc routine which transforms a standard 2D homogeneous FE mesh into a 3D orthotropic elastic model with non-linear interfaces connecting contiguous elastic elements (cells). The proposed method is applied to a hemispherical dome and a cloister vault, with abundant experimental and numerical data available in the literature to compare with. Sensitivity analyses are conducted in order to have an insight into the reliability of the method, which proved excellent predictivity capabilities, as far as both the peak load and the activated failure mechanism are concerned
Seismic vulnerability procedures for historical masonry structural aggregates: Analysis of the historical centre of Castelpoto (South Italy)
No full textIn historical centres, it is very difficult to analyse masonry buildings as independent structures since they have common wall panels with adjacent structural units. These types of building compounds interact with each other under seismic actions, so their behaviour differs from that of individual buildings considered isolated structures. In this framework, multilevel procedures for assessing the vulnerability of masonry building aggregates are examined in the paper and illustrated in detail through the application of a case study in Castelpoto, a municipality of Benevento (Italy). From one side, an index-based evaluation methodology is proposed, appropriately calibrated on the results of the analysis of macroelements on a significant number of grouped buildings, also considering the interactions among adjacent buildings. On the other side, a method based on mechanical analysis is applied at the building scale to evaluate, more realistically, the seismic behaviour of clustered structural units through suitable capacity and fragility assessments
A simple homogenized micro mechanical model for the analysis at the collapse of out-of-plane loaded masonry walls
No full textThe paper presents a simple micro-mechanical model for the limit analysis of out-of-plane loaded masonry walls by means of homogenization techniques. In this framework, masonry thickness is subdivided into several layers and for each layer polynomial distributions for the stress fields are a-priori assumed inside a fixed number of sub-domains. In this way, a simple linear programming problem is derived with the aim of obtaining out-of-plane homogenized failure surfaces of masonry. Finally, such strength domains are implemented in FE limit analysis codes for upper and lower bound analyses on entire masonry panels out-of-plane loaded. One of these numerical analyses is reported in order to show the reliability (in terms both of collapse loads and failure mechanisms) of the model at hand in comparison with experimental data
A kinematic limit analysis approach for masonry buildings: in- and out-of-plane failure mechanisms
No full textHistorical and existing masonry structures have usually an inadequate resistance to horizontal actions. Furthermore, historical city centres present high vulnerability under horizontal
loads and this is mostly due to the absence of adequate connections between the various parts [1] [2]. This characteristic leads to overturning collapses of the perimeter walls under seismic loads and combined in- and out-of-plane failures. Even if limit analysis is not sufficient for a full structural analysis under seismic actions, since it does not provide displacements at failure, it can be used in order to have a quick estimation of both collapse loads and failure mechanisms [3].
In this paper, the micro-mechanical model presented by the authors in [4] and [5] for the limit analysis of respectively in- and out-of-plane loaded masonry walls [6] is utilized for the 3D analysis of entire buildings. In the model, admissible and equilibrated polynomial stress fields are imposed in order to estimate the macroscopic masonry failure surface. Finally, such surface is implemented in a FE kinematic limit analysis code and an example of technical relevance is discussed in detail
Modulation de l’excitabilité d’unités motrices isolées du muscle fléchisseur du poignet par les afférences cutanées de la pulpe de l’index chez l’homme
No full textLes effets spinaux produits par une stimulation mécanique ponctuelle appliquée sur la pulpe de l’index ont été précédemment étudiés, chez l’homme, par la technique du réflexe-H (Cavallari et Lalli, Exp Brain Res 120 :345-351, 1998). Les afférences cutanées ainsi stimulées entraînaient une inhibition de courte latence du réflexe-H évoqué dans le muscle fléchisseur du poignet (FCR), immédiatement suivie par une facilitation de longue durée. Par ailleurs, la stimulation électrique des nerfs digitaux de l’index était inefficace.
Le but de cette étude est de montrer que la probabilité de décharge d’unités motrices isolées (UM) du FCR est modulée de la même façon que le réflexe H, après stimulation ponctuelle mécanique, ou électrique, de la pulpe de l’index.
28 unités motrices ont été étudiées par la technique du post stimulus time histogramme (PSTH) sur 5 sujets volontaires sains. Ainsi, après stimulation mécanique de l’index (3xPT, seuil de perception, durée:10ms) une inhibition caractérisée par une latence de 10,4±1,4ms (11/14 UM) est suivie d’une facilitation (14/14 UMs) de longue durée. Le même effet biphasique (latence de l’inhibition 9,6±1,3ms) est observé après stimulation électrique focale (2xPT, durée: 0,8ms) de la pulpe de l’index. Toutes les latences sont exprimées par rapport à la latence de l’excitation monosynaptique homonyme Ia évoquée, dans le FCR, par la stimulation du nerf médian au pli du coude.
Ce travail montre que la stimulation focale électrique ainsi que la stimulation mécanique des afférences cutanées, modulent de manière biphasique la décharge d’une unité motrice isolée, confirmant l’effet observé en réflexe H. Par ailleurs, il est aussi démontré une distribution homogène des voies inhibitrices et excitatrices sur les mêmes motoneurones, écartant, dans ce cas là, l’hypothèse d’une distribution dishomogène des effets produits par les afférences cutanées sur les motoneurones à plus bas seuil (Garnett R, J Physiol 303:351, 1980; Nielsen J, Acta Physiol Scand 147:385, 1993)
A micro-modeling approach for the prediction of TRM bond performance on curved masonry substrates
No full textRetrofitting of arches, vaults and domes is needed for vulnerability mitigation of historical structures. Lately, the external application of composite materials embedded within an inorganic matrix addressed the compatibility issues related to FRP applications. Great efforts have been made for a correct identification of tensile and bond properties of TRM reinforcement, but scarce data are available for understanding the effect of curvature in debonding. This paper provides a numerical approach that enables to predict the reinforcement performance on curved masonry elements, when the same is designed without having specific single lap shear tests for the adopted materials. Such an approach relies on a separate modeling of each constituent material of the reinforcement and the substrate: matrix, fibers and the interface between them, and bricks and mortar joints. The FE-based software Abaqus is used for the simulations, addressing the non-linear material properties by means of the CDP constitutive model. In order to calibrate and validate the proposed numerical approach, experimental data are used and through a comparison of the load–displacement curves obtained the capabilities of the method are discussed. Finally, an extension of such approach to curvatures not experimentally tested is presented, opening the way to future applications of the approach
A micro-mechanical model for the homogenized limit analysis of out-of-plane loaded masonry walls
No full textThe paper presents a novel micro-mechanical model for the homogenized limit analysis of out-of-plane loaded masonry walls. In the framework of homogenization combined with limit analysis, masonry thickness is subdivided in several layers and for each layer polynomial distributions for the stress fields are a-priori assumed inside a fixed number of sub-domains. In this way, a simple linear optimisation problem is derived in order to obtain out-of-plane homogenized failure surfaces of masonry. Then, the surfaces so recovered are implemented in FE limit analysis codes for upper and lower bound analyses on entire masonry panels out-of-plane loaded. Some of these numerical investigations are reported in the paper in order to show the reliability of the results obtained (in terms both of collapse loads and failure mechanisms) in comparison with experimental evidences
Numerical validation of a heterogeneous FE approach for the analysis of TRM debonding on curved masonry substrates
No full textRetrofitting of curved masonry elements as arches, vaults and domes is often a key aspect in a process of vulnerability mitigation of historical structures. Lately, the external application of composite materials embedded within inorganic matrix has met the requirements suggested by ISCARSAH guidelines. In literature, great efforts have been addressed for a correct identification of tensile strength and ideal bond length of TRM reinforcement. On the other hand, few data are available for a deep understanding of the effect of the curvature on the bond properties. This paper aims to provide a numerical tool enable to predict such a fundamental aspect when a reinforcement on curved masonry elements is designed. Experimental data are used and through comparison of curves load-displacement, the capabilities of the method are shown
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