1,720,960 research outputs found
New formulation of ductility reduction factor of RC frame-wall dual systems for design under earthquake loadings
No full textAny design of standard structures in keeping with seismic safety norms is usually founded on an approach characterised by force-based design. Research has proven, over the course of several decades, that such an approach has a solid basis and can easily be applied by the engineers in charge of the design project. Furthermore, when taken in conjunction with principles of capacity design, the force-based approach is effective against premature structural failures. The force-based design approach, however, suffers from a number of shortcomings, especially regarding the way it has been employed in seismic design codes of recent years. One of the weaknesses can be attributed to the way the base shear is calculated via a reduction factor that has been defined a priori and that remains constant for a certain structural system typology. The outcome of depending on the same design input shows that structures identical in type but variant in geometry undergo varying ductility demands and exhibit, therefore, a different seismic performance. In this research, a procedure for assessing force-reduction factors of RC frame-wall dual systems is developed, by combining the analytical formulations proposed by Zerbin et al. (2019) for wall and frame systems, separately. These analytical formulations make it possible to combine global and local ductility demands, thereby allowing a calculation of the factors of force ductility reduction that result in balanced local ductility demands and the predicted levels of damage. The proposed method is based on empiric expressions that merely require – as input data – the information available when starting the design process. The proposed formulation is applied to a set of frame-wall structures and tested by means of both nonlinear static and dynamic analyses. The current study has produced conclusions showing that, with respect to such dual system structures' seismic behaviour, the procedure proposed herein yields a more accurate assessment of than the approach being currently used by design guidelines; in turn this method may provide a valid contribution to the evolving guidelines of future seismic design codes
A Novel Friction Damper for Seismic Retrofit of Precast RC Structures with Poor Connections
No full textPrecast RC structures are commonly adopted for industrial and commercial buildings, to build huge spaces with limited costs and construction times. Due to the lack of efficient seismic regulations until recent times, and adequate assessments of seismic hazard, a huge number of seismically inadequate precast RC buildings are spread through Southern Europe territories. Workers’ and users’ safety requirements, and the preservation of high-value facilities and stocks, demand the adoption of effective retrofit techniques for earthquake risk mitigation. For this structural typology, connections between structural elements are often crucial for carrying lateral loads, such as earthquakes. This study presents an innovative device that acts as beam-to-column joint and as damper at once, with bidirectional dissipative capacity. Very easy to install, low cost and reusable after the main shock, this novel Bidirectional Rotation Friction Damper (BRFD) has been conceptualized and designed to improve the seismic performance of such structures by excluding the brittle failure of structural and non-structural elements. Preliminary experimental tests performed at the University of Ferrara, Italy, have proved the high-damping capacity of this novel device. BRFD effectiveness on a precast structure has been explored using nonlinear time-history analysis accounting both low- and high-intensity Italian earthquakes. Numerical modelling has shown that no beam’s slippage on column top section and no column crisis can occur in both building directions when BRFD are properly implemented. The designed devices provide a global improvement of the seismic performance of the building, preventing any structural and non-structural damage even for the more critical Near-Field events
Advanced Techniques for Pilotis RC Frames Seismic Retrofit: Performance Comparison for a Strategic Building Case Study
No full textPilotis buildings have widely spread out in developed countries since World War II onwards. From the structural point of view, Pilotis RC frames exhibit substantial lack in ductility capacity and shear resistance localized at the first floor, since they have been mainly realized before the seismic codes’ era. The present study shows the performance comparison of four advanced retrofit techniques when applied to typical Pilotis RC frame designed for gravity loads only according to Italian building code of ‘60s. A preliminary investigation has been performed to select non-linear numerical models suitable to describe the considered RC frame behavior, involving flexural inelastic hinges of RC beams and columns and in-plane axial inelastic hinges of masonry infill panels. Two seismic retrofit projects have been designed at a local level, by strengthening the masonry infilled panels with Fiber Reinforced Cementitious Matrix (FRCM) technique and alternatively by replacing infilled panels with prefabricated panels disconnected from the structure, so that no infill/frame interaction occurs. Two more retrofit projects have been designed at a global level, in order to improve the overall structural performance making use of energy dissipation and, alternatively, base isolation techniques. Nonlinear time history analysis and structural assessment have been carried out for the as-built case as well as for the four retrofit solutions according to Eurocode 8 and Italian Building Code, in order to highlight the structural deficiencies and relative improvements, respectively. Performances offered by the proposed retrofit techniques have been finally compared in terms of structural behavior, expected damage, and economic impact
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 Retrofit of a Precast RC School Building with External BRBs in Northern Italy
No full textPrecast RC structures have been widely used in Italy during past 60 years and mainly adopted to host industrial and commercial activities, as well as school buildings, such as the “Ercole I d’Este” in Ferrara. For these structures, quite common features are poor connections between structural elements, along with limited shear strength and flexural ductility of columns. Many of them were designed for gravity loads only, since past regulations did not imposed earthquake loads application for the whole Italian territory. Recent seismic events have proved how much these structures are prone to premature and fragile collapse, as observed during the 2012 Emilia Earthquakes when they caused several casualties, injured people, and displaced. This study presents the application of Buckling Restrained Braces (BRBs) as advanced retrofit solution for a sustainable upgrading of precast RC structures seismic performances. BRBs are implemented to add significant damping to traditional external seismic steel bracings, and seismic forces are transferred to external bracings thanks to a proper floor and roof reinforcement. Direct displacement-based design is applied to design BRBs, optimizing their sizing and plan position. BRBs effectiveness on the RC precast structure upgrading has been investigated using nonlinear time history analysis. The designed retrofit solution provides a global improvement of the seismic performance of the building to prevent any structural and nonstructural damage with sustainable costs. The major benefit of BRBs application respect to traditional braces is the reduction of external bracing and their foundations which leads to significant savings
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