1,720,965 research outputs found
Numerical insight on the interaction effects of a confined masonry tower
No full textThe present paper provides a numerical insight into the structural behavior of a confined masonry tower. The study is carried out in relation to the Gabbia Tower, the tallest historical masonry tower in the city of Mantua (northern Italy), which is surrounded by multistory masonry buildings on all its sides. Three 3D FE numerical models are critically compared to investigate the sensitivity of the structural behavior of the tower with respect to the adjacent buildings, both in the linear and non-linear fields. Firstly, the tower is studied as a fictitious building isolated from the context, then two different constraints are considered for modeling the interaction between tower and buildings. In the first case, linear elastic springs are inserted along the height of the tower; while the other one focuses on the effect provided by the adjacent buildings, whose walls are modeled as monolithic elements joined to the main body of the tower. The validation of the FE models is carried out in the linear field by comparing mode shapes and frequencies resulting from the numerical modal analysis with the available experimental data provided by the ambient vibration test conducted in 2012. The effect of the different constraints on the seismic response of the tower is then investigated by performing a set of non-linear dynamic analyses and considering the accelerograms recorded during the earthquake of May 29, 2012 by the fixed station located in Mantua as seismic input. Numerical results indicate the modeling of the surroundings as an essential step for a realistic analysis of confined towers. In particular, the simulations highlight advantages and limitations of the proposed modeling approaches of the constraints, both in the linear and non-linear fields
On the characterization of materials and masonry walls of historical buildings: Use of optical system to obtain displacement maps in double-flat jack tests
Full text linkAmong the testing techniques aiming at the mechanical characterization of masonry, the double flat-jack testing method is widely adopted to identify the local value of significant parameters needed to perform structural analyses, such as elastic modulus, Poisson’s ratio and compressive strength. The experience gained from many applications has allowed not only to collect experimental data concerning different types of masonry, but also to highlight the difficulty in the interpretation of the results and the limitations of both single and double flat-jack tests. Although the accuracy of the flat-jack technique in detecting strength and deformability behavior of masonry is still debated in the technical literature and practical activities, changes in the testing procedure aiming at ascertaining the validity of the test results have not been formally defined yet. After a brief description of the standard test procedure and its uncertainties, the present paper proposes an upgrade of the test procedure for improving the level of reliability of the test results. In particular, an experimental case study related to a historical brick masonry building located in Italy is presented to point out the additional information necessary to validate the results of the testing process
Interpretation of collapse modalities for a timber roof truss
No full textRoof structures in historical buildings are often based on complex timber trusses; this is typically the situation of theatre buildings, where a wide room is present and large spans have to be covered. Several studies have been done on such structural systems showing that, in the case of complex roof systems, connections between timber elements were conceived in the past mainly to resist vertical loads corresponding to symmetrical patterns, with no consideration of eccentric loads and horizontal forces. In the paper, this problem is investigated with reference to the specific case study offered by a theatre, where a queen post truss was adopted for the roof system and the sudden collapse of one truss has occurred. The theatre, which is located in northern Italy, was built at the beginning of the 19th century. Although some modifications were made through time, the roof structure has preserved the original configuration. A precise identification of the real structural conditions has been obtained on the basis of the results of laser scanning and photogrammetric surveys. On this basis, numerical models have been developed in order to analyse a variety of load scenarios compatible with the observed structural collapse, with the final purpose of highlighting possible deficiencies in the original structural configuration, in line with the collection of similar cases which are reported in the literature
The seismic sequence of 2016–2017 in Central Italy: a numerical insight on the survival of the Civic Tower in Amatrice
No full textThis work is aimed at the numerical interpretation of the evolution of damage and collapses observed on the Civic Tower of Amatrice, caused by the main events of the seismic sequence of 2016 in the Apennine area of Central Italy. In particular, the study considers the response of the tower with reference to the two main events, occurred on August 24th and October 30th, 2016 respectively. Non-linear dynamic analyses were carried out by developing a finite element model and the behaviour of the tower was investigated with reference to the damage and partial collapses produced by the main events. In dynamic numerical analyses, the accelerograms corresponding to the main seismic events obtained with the study of the site effects were used as seismic input. Moreover, studies have been carried out to understand if and which of the interventions of reinforcement/seismic improvement, realized at the beginning of the years ‘80, have been determinant to limit the damage, avoiding the complete collapse of the tower. The results of the study, on the one hand, allow to highlight a good correspondence between the evolution of the actual damage observed on the tower and the damage assessed by numerical analyses thus demonstrating the validity of the numerical models set up for the analyses. On the other hand, however, they have made it possible to underline how the presence of the improved material and structural reinforcement interventions carried out at the beginning of the years ‘80 have contributed to avoid the complete collapse of the tower
Seismic vulnerability of masonry buildings: Numerical insight on damage causes for residential buildings by the 2016 central Italy seismic sequence and evaluation of strengthening techniques
Full text linkThis study aims at investigating the causes of damage and collapse of several residential masonry structures during the devastating seismic sequence that hit Central Italy in 2016. After analyzing the structural features of affected buildings, an extensive series of numerical analyses is performed for a sample two-story masonry building to better understand its seismic vulnerability and suggest valuable hints for the reconstruction of historical city centers. Each analysis is carried out by adopting realistic hypotheses concerning material properties, connection among multi-leaf walls, different roofing systems (e.g., use of RC slabs at the top of the buildings), and the presence of rigid or flexible floors. Numerical analyses consist of modal and non-linear dynamic analyses, the latter using input accelerograms recorded during the main shocks of 2016 by the permanent accelerometric station of Amatrice (one of the most affected municipalities). For non-linear dynamic analyses, an elasto-plastic constitutive law with reasonable damage parameters in tension is adopted. Numerical results highlight good correspondence with observed behavior of residential low-rise buildings after the main seismic events in Amatrice, demonstrating the validity of the numerical approach. Moreover, the poor quality of the constitutive masonry material and the insufficient rigidity of floors and roofing systems are identified as the main causes of seismic vulnerability and, consequently, of collapse mechanisms. It is found that high quality masonry and well-connected walls play a crucial role in limiting damage formation and reducing global seismic vulnerability
The 2016 Central Italy seismic sequence: linear and non-linear interpretation models for damage evolution in S. Agostino’s church in Amatrice
No full textAn extensive numerical investigation of the structural behavior of the masonry church of Sant’Agostino in Amatrice (Italy) during the 2016–2017 seismic sequence is presented. The seismic performance of the church is studied in relation to the most energetic shocks of the sequence, occurred on August 24th, 2016, and October 30th, 2016, whose seismic parameters (PGA, Trifunac duration, Arias intensity, destructiveness potential factor) are analyzed in detail. In particular, a comparison between ground motion data recorded by different stations is presented in order to evaluate the influence of local amplification effects on the structural behavior. To achieve this goal, the ground motion data recorded by the permanent accelerometric station (AMT) located in Amatrice on type B soil and belonging to the National Accelerometric Network (RAN) are firstly considered. Then, they are critically compared with those provided by an accelerometric station temporarily installed after the first main shock in the downtown area close to the church site, showing a clear amplification due to the site effects. The dynamic behavior of S. Agostino’s church is numerically investigated by carrying out a set of non-linear dynamic analyses on the 3D finite element model of the church developed in Abaqus CAE and considering as seismic input both the accelerograms recorded by the AMT fixed station and those including the local amplification effects. Non-linear properties of materials are taken into account by defining an elasto-plastic constitutive law with reasonable damage parameters in tension. Numerical results are evaluated in terms of displacement time-history of some relevant control points located on the masonry walls and maps of tensile damage cumulated at the end of the simulations. Numerical results are in good agreement with the evidence based behavior of the structure, thus validating numerical simulations as effective tools for seismic analysis of masonry buildings. Furthermore, a hypothetical strengthening intervention concerning the improvement in masonry mechanical properties is implemented in the model to investigate its positive role in preventing collapse. In the latter case, the approach provides useful hints in interpreting the behavior of the church under the application of repeated accelerograms
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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Failures and damages of historical masonry structures induced by 2012 northern and 2016–17 central Italy seismic sequences: Critical issues and new perspectives towards seismic prevention
No full textThe work analyses some observed structural criticalities in historical masonry structures emphasized by the seismic events of May 2012, in Emilia, and of August-October 2016, in Central Italy. The causes that brought to different damage scenarios in the historic centres and to the different degree of damage evolution of the buildings, have been investigated, comparing their construction and dynamic features, such as the natural vibration periods of the different construction typologies with the spectral accelerations and the amplification periods distinctive of the seismic events. In particular, starting from the evidence of the damage observed on the built heritage of some of the centres most affected by the two seismic sequences, and from the characteristics of the seismic signals recorded at the considered sites, it is proposed a study which analyses some criticalities, in relation to preventive purposes of the technical standards, specifically with reference to historical constructions. Among the main criticalities highlighted in the present work, it should be noted the remarkable difference between the design spectra and the spectra of the recorded seismic events (real earthquakes), and the circumstance that in reality the constructions generally are interested by more seismic shocks (multi-events) characterized by higher intensities with respect to the ones expected by the building code. Such feature gives rise to a criticality for the operators acting in the emergency phases of rescue and temporary securing, who find themselves operating in high hazardous conditions, due to the high vulnerability of already damaged built heritage induced by the main-shock, and by the high probability (near certainty) that, in the short period, events having intensities and characteristics similar to the main-shock may occur. Moreover, the evolution of the damages, with progressive crumbling associated to global or partial collapses, due to the sequence of shocks (multi-events), which had interested thousands of buildings in the historical centres (and not only) subjected to the seismic sequence, bare witness of criticalities in the preventive approach proposed at national level. The analysis of the criticalities highlighted in the present work allows to envisage an approach which considers for the structures, historical or not, adequate performance requirements with respect to the emergency, temporary and permanent securing phases, accounting for the multi-event seismic context typical of the Italian territory
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