1,721,011 research outputs found
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
General methodological approach for the seismic assessment of masonry aggregates
No full textStrong earthquakes have recently shown the vulnerability of masonry structures. In Italy, most of the historical centres are characterized by adjacent masonry structures connected in aggregate that have been subjected to structural and functional changes during time. Their structural behaviour shall be studied to avoid catastrophic outcomes after seismic events. In the technical literature, many studies are available to identify the most vulnerable structures in historical centres from a macroscopic point of view, or the seismic behaviour of some typical structures was studied in detail with sophisticated numerical methods providing a specific seismic vulnerability assessment. However nowadays there is not a general and standard procedure available, mostly methodological, based on well-known analysis methods, that can be followed to evaluate the structural behaviour under seismic actions of any building aggregate, and that allows to identify effective retrofitting interventions. Moreover, national regulations typically do not provide a standard procedure that can be followed by practitioners for such kind of problems. Thus, the purpose of this paper is to suggest a protocol to be used in common design, based on a broad blend of analyses that can be carried out with commercial software. It relies in a variety of numerical analyses, spanning from simple eigenvalue simulations to full 3D pushover computations, assuming different hypotheses for the material behaviour. The suggested method has been applied and benchmarked to an ex-monastery in northern Italy and several structural considerations to provide a sufficient insight useful for practitioners are provided
PROPOSAL OF A GENERAL METHODOLOGICAL APPROACH FOR THE SEISMIC ASSESSMENT OF HISTORICAL MASONRY AGGREGATES
No full textThe vulnerability of masonry aggregates has been highlighted by recent strong earthquakes. Most of the Italian historical centres are characterized by adjacent masonry structures connected in aggregate that have undergone to structural and functional changes over time. Their seismic vulnerability shall be studied to avoid disastrous outcomes. Many studies are available in the technical literature to identify the most vulnerable structures in historic centres from a macroscopic perspective, furthermore the seismic behaviour of some typical structures was studied in detail using sophisticated numerical methods to provide a specific seismic vulnerability assessment. However nowadays there is not a general and standard procedure available, mostly methodological, based on well-known analysis methods, that can be followed to evaluate the seismic vulnerability of any building aggregate, and that allows to identify effective retrofitting interventions. Moreover, common national regulations do not provide a standard procedure for practitioners to follow in such cases. Thus, the purpose of this contribution is to show a protocol to be used in common design, that has been developed in a wider work, and it is based on a broad blend of analyses that can be performed with low-cost software. With different hypotheses and modelling assumptions, numerical analyses range from simple eigenvalue simulations to full 3D pushover computations. The suggested method has been presented in a wider work where it has been applied and benchmarked to the ex-monastery of Santa Maria della Pace in Piacenza, Italy
Italian Seismic Damage Prevention Policies for the Built Heritage: Efficacy and New Perspectives
No full textEarthquakes that occurred in Italy in the last 50 years—in particular the most recent seismic events which affected Northern and Central Italy in 2012 and 2016–17—have shown the high intrinsic vulnerability of existing structures. Many historical structures and old town centers suffered partial or total collapse, even in the presence of seismic improvement interventions. This fact underlines, on the one hand, the wrong definition of the seismic hazard that in most cases largely exceeded the design one, and on the other hand, the limitations of seismic preventive policies prescribed by the Italian building code, especially for listed buildings. Furthermore, sequences of shocks with similar magnitude are typical of Italian earthquakes. In these conditions, namely seismic multi-events conditions, the existing buildings suffered progressive and severe damage, overcoming the life safeguard and collapse limit states defined by the national prescriptions. This condition results in a high level of risk for operators acting in the post-earthquake phase, since aftershocks may cause further collapses of already damaged buildings. Severe damage was observed also in almost all the historical listed buildings. In the seismic multi-event context, especially in Central Italy, the damage evolution brought to the complete loss of historical structures. Italian regulations prescribe very limited seismic retrofitting works for listed buildings, that cannot even cope with the first shock of the seismic sequence. In light of this, new seismic preventive policies should be adopted, at least in areas with moderate-high seismic hazard, to safeguard people’s lives and avoid the loss of cultural heritage. Moreover, strong shock sequences, occur frequently in Central Italy; thus, new preventive policies would be required to limit damage accumulation and, therefore, reconstruction costs
'HYBRID' FULL MODELS FOR SEISMIC ASSESSMENT OF MASONRY AGGREGATES THROUGH PUSHOVER ANALYSIS
No full textMost of the historical city centres in Southern Europe are made up of masonry buildings clustered in aggregate, which are a result of the urban tissue transformation over time. Recent earthquakes have shown their high vulnerability because buildings were built without any anti-seismic criterion, relying on simple rules of thumbs. Since the seismic behaviour of masonry aggregates cannot be a priori predicted - because of complex geometries, presence of materials having different behaviours and interactions among adjacent buildings - accurate analyses, such as pushover analyses, shall be performed. Masonry aggregates are typically characterized by the presence of different structural typologies, thus pushover analyses are generally performed on partial models, representing significant portions of the whole aggregate. The critical point in this type of analysis is the identification of the minimum length of the portions of the neighbouring walls that actually contribute to the extra-redundancy of the structural system, which cannot be taken into account within partial models. Hence the idea to consider “hybrid” full models, in which the material behaviour is assumed non-linear only for the portion subject of investigation, while it is assumed linear elastic for the context. This contribution shows the results - part of a wider work - obtained by means of pushover analyses performed for the ex-monastery of Santa Maria della Pace in Piacenza, Italy, on full and partial models of the entire aggregate with different material modelling assumptions, and the model that best represents the actual behaviour of masonry aggregates is proposed
COMPARISON OF THE RECORDED SEISMIC SIGNALS FOR THE 2012 EMILIA AND 2016 CENTRAL ITALY SEISMIC SEQUENCES WITH THE DESIGN EARTHQUAKES BASED ON THE PSHA APPROACH
No full textThe recent seismic sequences occurred in 2012 in the Emilia region and in 2016 in Central Italy have confirmed the high level of vulnerability typical of masonry historical buildings and historical centres. Among these, the historical centre of Amatrice was razed to the ground and most of the historical buildings of municipalities in the epicentral area suffered partial or total collapse. Ground motion recordings highlighted a remarkable difference with the design earthquakes provided by the national seismic hazard map, which is based on the PSHA (Probabilistic Seismic Hazard Assessment) approach. Specifically, the response spectra of the signals recorded at Finale Emilia and Mirandola (2012) and at Norcia and Amatrice (2016) have been compared to the design spectra prescribed by the national building code; from comparison, the strong underestimation of the design spectral accelerations is evident, especially for the historic centre of Amatrice, due to the additional effect of local amplification. All recent Italian earthquakes (L'Aquila 2009, Emilia 2012, Central Italy 2016) and many others around the world, have shown that the PSHA approach does not provide reliable results in case of severe events. On the contrary, the technical literature shows that the NDSHA (Neo-Deterministic Seismic Hazard) approach generally provides reliable results. The need to update the seismic regulations, therefore, is clear in view of a preventive policy against the collapse of historic centres and monuments, based on the correct definition of seismic hazard levels. In the present contribution the analysis of the above seismic events is presented, being part of a wider analysis on the effects produced on the built heritage by seismic sequences
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
Semi-automatic calibration of numerical models for the seismic safety assessment of masonry towers embedded in building aggregates
No full textThe present work addresses the topic of automated calibration of numerical models starting from the experimental characterization of the structure's dynamic behaviour. The importance of the topic is well known in the literature, especially in cases where it is necessary to have at disposal validated numerical models, necessary for the correct evaluation of the safety of existing buildings. Generally, the calibration problem is developed with a manual approach (manual tuning), with a positive outcome whenever there is a good knowledge of the boundary and internal constraint conditions and the elastic mechanical properties of the construction's constituent materials. Conversely, the positive outcome is particularly difficult to achieve manually when there are non-homogeneous and/or complex structures, as in the cases of historic masonry structures, which are often the result of constructions carried out at different times, organized in aggregates whose interaction between the portions is not simple to understand. For this purpose, the present work, using commercial software and specially prepared routines, illustrates a semi-automatic procedure, which employs genetic algorithms, suitable for the optimized identification of the numerical model that best represents the structure's experimental dynamic behaviour. The procedure is presented with reference to two case studies: the Gabbia Tower historic masonry aggregate in Mantua and the bell tower of the Monastery of the Ursuline nuns in Capriolo, Brescia. In the first case, in addition to the experimental dynamic characterization, a good instrumental characterization of the tower's masonry mechanical properties is available. In the second case, alongside a good experimental dynamic characterization, only a qualitative estimate of the masonry mechanical properties, based on visual inspections, is available. The two case studies allow for testing the validity of the numerical models’ calibration procedure, necessary for their application in the field of safety checks. Finally, for the case studies analysed the work presents an assessment of seismic vulnerability starting from the models identified with the semi-automatic procedure. The seismic vulnerability assessment was obtained using non-linear static analysis following the N2 method
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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