1,720,968 research outputs found
A simplified design procedure for seismic upgrade of frame structures equipped with hysteretic dampers
Full text linkThis paper presents a simple and affordable design procedure for the seismic upgrade of frame structures equipped with hysteretic dampers. The proposed framework is aimed at leading the designer to proportion the damper device(s)) in order to achieve a desired structural performance level. According to the method, the structural system composed by frame and dampers is replaced by an equivalent Single Degree of Freedom (SDOF) system, characterized through its secant stiffness and equivalent viscous damping, both defined in relation to a “performance point” which is assigned on the basis of the allowable damage of the frame and on the first mode deformation of the main structure. The global stiffness and strength of the equivalent SDOF system are then distributed along the height of the frame according to a stiffness-proportionality criterion, and the properties of the damper units are calculated depending on the chosen layout. Two case-studies relevant to as many reinforced concrete frames are provided to demonstrate the effectiveness of the suggested procedure, obtaining a satisfactory agreement between the design target and numerical capacity curves. Non-linear dynamic analyses are further performed to assess the reliability of the methodology
Towards Improved Floor Spectra Estimates for Seismic Design
No full textCurrent codes incorporate simplified methods for the prediction of acceleration demands on secondary structural and non-structural elements at different levels of a building. While the use of simple analysis methods should be advocated, damage to both secondary structural and non-structural elements in recent earthquakes have highlighted the need for improved design procedures for such elements. In order to take a step towards the formation of accurate but simplified methods of predicting floor spectra, this work examines the floor spectra on elastic and inelastic single-degree of freedom systems subject to accelerograms of varying seismic intensity. After identifying the factors that appear to affect the shape and intensity of acceleration demands on secondary structural and non-structural elements, a new series of calibrated equations are proposed to predict floor spectra on single degree of freedom supporting structures. The approach uses concepts of dynamics and inelasticity to define the shape and intensity of the floor spectra at different levels of damping. The results of non-linear time-history analyses of a series of single-degree of freedom supporting structures indicate that the new methodology is very promising. Future research will aim to extend the methodology to multi-degree of freedom supporting structures and run additional verification studies
Experimental evaluation of extra-stroke displacement capacity for Curved Surface Slider devices
No full textCurved Surface Slider (CSS) devices have been widely used in recent years for the reduction of seismic vulnerability of structural systems. Recent risk assessment studies have revealed that base isolated systems can be characterized by higher seismic risk with respect to their fixed-base counterparts. It is believed that this unexpected outcome is, partly, due to the definition of collapse condition that has traditionally been adopted for base isolated structures, which is somewhat stricter than for many other structural systems. More specifically, in most circumstances, a base isolator is assumed to collapse once the sliding pad reaches maximum geometrical displacement, which corresponds to the edge of the sliding surface. This paper summarizes the results of an experimental program that investigated the response of CSS devices under extreme seismic loading, with focus on base isolation devices stressed beyond their nominal capacity. A full-scale Double CSS prototype with three different low-friction materials was tested with cyclic signals and in the context of a hybrid simulation. A low value of peak sliding velocity has been assumed, in comparison to realistic values experienced during earthquake excitations, in order to be able to control the stability of the force response for the whole duration of the performed tests. The results collected were able to assess the effective response of CSS devices, when design geometrical characteristics are overcome within specific defined limits, and to formulate suitable numerical models to deal with extra-stroke response of DCSS in dynamic analysis
Numerical assessment of concentrated plasticity models of ductile RC frames in non-linear dynamic analyses
No full textThe study evaluates concentrated plasticity formulations used to model ductile reinforced concrete frames in non-linear dynamic analyses. Four frames with increasing number of stories (2, 4, 8 and 12) are modelled in OpenSees and assessed under a set of spectrum-compatible input ground motions, investigating the effect of modelling decisions on the length of the plastic hinge region and the flexural stiffness of the cracked concrete section. The results highlight that modelling choices mainly affect the estimates of inter-story drift ratio and maximum base moment, while effects on floor acceleration and maximum base shear are low; the effective flexural stiffness of cracked concrete must account for the axial load in the structural member
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
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
Seismic performance of bridges during the 2016 Central Italy earthquakes
No full textThis paper focuses on the structural performance of existing masonry and reinforced concrete bridges which were surveyed in the aftermath of the 2016 Central Italy earthquakes. Typical bridge vulnerabilities are first reviewed, as they provide a reference for the response of the bridges that were damaged by the 2016 earthquake swarm. Case studies are then discussed and preliminary numerical analyses are carried out to interpret the observed failure modes. In general, all surveyed masonry bridges experienced some extent of damage, particularly when built with poor-quality materials and subjected to geotechnicalinduced effects. However, they offered a robust response in terms of collapse prevention. The majority of existing reinforced concrete bridges, although designed primarily for gravity loads, exhibited acceptable performance; however, local damage due to the poor maintenance of the structural systems was observed, which affected primarily the non-structural components of the bridges
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