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Seismic reliability of buildings isolated with rubber bearings
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Long-term viscous effects of in-field tests on HDRBs-based seismic isolation systems
Get PDFPush and release tests on full-scale base-isolated buildings can be considered de facto as in situ verification tests of the actual behaviour of a base-isolation system. However, for isolation systems based on High Damping Rubber Bearings (HDRBs) the test response significantly depends on the pushing phase velocity. If this is quite low (due to the limited capacity of the hydraulic system), the free vibration response can remarkably differ from the expected one (considering nominal properties of HDRBs) due to the viscous behaviour of HDR compounds. Therefore, a model that adequately describes the viscous effects related to different strain velocities is crucial for correctly interpreting the experimental measurements obtained from the tests. This paper examines in detail the viscous effects observed in both laboratory tests conducted on a couple of HDRBs (type tests) and the experimental in-situ tests performed on a base-isolated structure equipped with an hybrid system comprising HDRBs and Low Friction Sliders (LFSs). A simple linear viscoelastic model of the HDRBs is developed based on type tests and then used to simulate the base-isolation system response. Results show that the model effectively predicts the experimental response (the pushing phase, the free vibration response and the final residual displacement) and that it can be used to verify that nominal properties of HDRBs (as well as friction of LFSs) are consistent with the design specifications, even if the recorded response differs from the expected one considering those parameters
Vision-based dynamic monitoring of a post-tensioned concrete bridge under vehicular traffic
No full textComputer vision for the purpose of structural dynamic monitoring of bridges has received much interest in recent years given the possibility of measuring displacement time-histories in absence of stationary points, using hardware that has accessible costs and is easy to operate. The review of the state-of-the-art shows that vision-based monitoring can potentially provide results equivalent to those obtained with the use of well-established contact sensors such as displacement transducers and accelerometers. Applications to real full-scale steel bridges and footbridges showed the possibilities of this technology in real-world conditions as well as difficulties and challenges posed by the surrounding environment. However, despite the many contributions published in the technical literature, very few applications involved post-tensioned concrete bridges, a very common solutions in the Italian road network and in many other countries. Characterized by a stiffer response as compared to steel bridges and footbridges, post-tensioned concrete bridges with their lower displacement magnitude and higher natural frequency might represent a more demanding testbed for vision-based monitoring. Accordingly, this study focused on the performance analysis of a vision-based structural monitoring system when applied to medium-span post-tensioned simply supported concrete bridges. The experimental outcomes show very interesting potentialities together with some critical aspects relevant to the vibrations induced in the tripod supporting the video camera that require attention to ensure the accuracy of the measurements
Statistical modelling of HDNR bearing properties variability for the seismic response of isolated structures
No full textThis paper reports some results of an ongoing Research Project called RINTC aimed at computing the risk of collapse of buildings conforming to the Italian Seismic Design Code. The project involves different areas of application (reinforced concrete, masonry, steel buildings, etc.) including reinforced concrete (RC) buildings equipped with isolation systems. In particular, this paper focuses on seismic isolation systems based on High Damping Natural Rubber (HDNR) bearings, which are widely employed for buildings and other structures. The aim of the paper is to evaluate the response dispersion due to the uncertainties in the seismic input as well as the variability of the isolation system properties. The study proposes a model to define the production variability of the bearing properties, taking into account the tolerance allowed in factory production control tests (FPCT) by the European code on anti-seismic devices (EN15129). To this purpose, in the first part of the paper, experimental results of groups of HDNR bearings belonging to different batches (classes) has been analysed, focusing on the values of shear stiffness and damping coefficient at design deformation and their correlation inside and between device groups. Both the intra-class and inter-class variability affecting the HDNR isolator properties are evaluated, by using a proper statistical model. Successively, the effect on the properties variability of the FPCT acceptance criteria provided by the European code is evaluated. In the second part of the paper, results of multi-stripe analyses carried out on a base isolated prototype consisting of a 6-storey RC building are presented for increasing ground motion intensities. In particular, several varied parameters of bearings are sampled starting from mean properties and by using the statistical model calibrated from test data. The influence of the bearings parameters variability on the most interesting engineering demand parameters (EDPs) and on collapse modalities is evaluated and discussed
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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