1,720,957 research outputs found
Steel exoskeletons for low-impact and Integrated seismic retrofit of existing buildings
No full textA significant portion of Europe's building stock was constructed following World War II. The absence of updates and enhancements has left this constructed environment exceedingly vulnerable to seismic events and energy inefficient. Due to PNRR tax incentives, there is a distinct necessity to delineate and supply qualified professionals with integrated, efficient, prompt, and cost-effective retrofit solutions. These treatments ought to be formulated with a comprehensive approach and grounded in the principle of Life Cycle Thinking. Traditional seismic retrofitting is often hindered by high costs, long execution times requiring building halts, and environmental concerns stemming from excessive material usage. This thesis investigates modern, non-disruptive, and environmentally conscious alternatives, focusing on external steel frame structures, or exoskeletons, which facilitate an integrated approach to resilience and energy improvements. Exoskeletons leverage the simplicity of steel assembly to reduce costs, minimize operational disruptions, and improve structural resilience. They are also compatible with dissipative or self-centering devices for improved seismic performance. The integration of energy-dissipating devices allows for the absorption and dissipation of seismic energy via inelastic deformations, thereby decreasing stress on the existing reinforced concrete structure. Such a retrofit provides a precise strategy, preventing excessive strengthening and concentrating on seismic demands. This leads to lower loads for new foundations and minimal impact on the original building, potentially diminishing overall intervention costs. In this scenario, innovative devices have been selected that can dissipate energy resulting from seismic activity, as well as seek to improve the resilience of the structure through devices that allow the building to return to its plumb position. To achieve this objective, the devices analyzed within this thesis work are rectangular and hourglass-shaped Buckling-Restrained Aluminum Shear-Yielding Plates; Dumbbell-shaped Steel Slit Dampers; Shape-Memory-Alloy-based dampers. This thesis applies and sizes several exoskeleton systems for strategic RC structures. The investigated retrofit strategies, all characterized as steel exoskeletons, include Dissipative Eccentric Braced Frames, Self-Centering Concentrically Braced Frames, Self-Centering Dual-Rocking Frames, and Base-Rocking Dual-Core Frames. The design of these interventions utilizes the Displacement-based Design approach. This method features constraints that may emerge when employed to build a retrofit for an actual case study. This thesis addresses several issues arising from the retrofit system or the as-built structure. The considerations encompass the energy dissipation capacity of the installed device and the connection system between the structure and the exoskeleton, which must guarantee the complete transmission of stresses from seismic forces while preserving rigid behavior, including the validation of the initial rigid diaphragm assumption. The retrofit strategies investigated in the matter of this work were thought and designed for real-world strategic RC buildings case studies. Their capacity to handle seismic forces was assessed starting from the linear (eigenvalue) modal and nonlinear (pushover) static analyses by Eurocode 8. Based on collapse mechanisms of each structure, the target displacement was defined, which is useful for designing the various interventions. The effectiveness of the retrofit strategy and the design procedure have been assessed by nonlinear Time-History analyses under a set of earthquake-strong ground motions selected and scaled for the Collapse Prevention Limit State based on the spectrum-compatibility rules of the Italian Code (2018)
Dissipative exoskeletons for seismic rehabilitation of RC buildings
No full textRelevant buildings like schools, public offices, assembly halls, and so on, should retain their structural integrity since their collapse could cause major human losses and significant economic impact. Moreover, such buildings should remain operational even during seismic retrofit work. This has stimulated the development of seismic retrofit solutions based on rapid, low-impact, and reversible interventions that can be done while the building is in use, removed and rapidly replaced if damaged due to earthquake, and integrated with energy efficiency measures. This situation has encouraged the use of external additive structures, commonly called exoskeletons, as a feasible solution for seismic retrofit. Typically, the research and applications deal with non-dissipative steel exoskeletons based on diagonal grids (diagrids) or external braces. This paper outlines the design and evaluation of dissipative exoskeletons. It focuses on a real school building case study, where both parallel and orthogonal exoskeleton configurations are employed. The dissipative exoskeletons are designed using a displacement-based design procedure. The effectiveness of the retrofit strategy is finally demonstrated by nonlinear time-history analyses under different sets of earthquake-strong ground motions
Influence of torsional effects in seismic retrofit of RC buildings
No full textThe nonlinear static procedures are very popular for the design and assessment of buildings subjected to earthquake ground motion in current structural engineering practice. Their application and relative accuracy are very relevant issues, especially in the case of seismic retrofit of irregular and/or high-rise buildings. Many retrofit design procedures are valid for low-rise buildings and/or neglect torsional effects and higher modes contribution. Often, the vibration properties are considered unchanged after retrofit, and the higher modes are neglected. Other ones are based on the proportional stiffness criterion (i.e., lateral story stiffness due to the additive structures is considered proportional to that of the original main structure). Still others rely on the hypothesis that the main structure remains elastic. Often, they neglect the interaction between the main structure and the additive structures used for retrofit. These are very significant drawbacks in the case of plan-asymmetric buildings, where torsional effects are important. In this case, the seismic response is dominated by harmful torsional effects and, thus, the retrofit strategy should significantly modify the dynamic response. To overcome such drawbacks but still keep the simplicity of using equivalent pushover analysis, this paper develops a “two-step” pushover procedure for seismic retrofit of plan-asymmetric buildings using buckling restrained braces based on steel hysteretic dampers (HBF). To this aim, a real case-study school building has been considered in the analyses. A design method has been implemented to size buckling restrained braces to be placed on selected spans and stories of the building. The effectiveness of the retrofit strategy has been finally demonstrated by nonlinear time-history analyses under different sets of earthquake-strong ground motions
DISSIPATIVE STEEL EXOSKELETONS FOR SEISMIC RETROFIT OF RC BUILDINGS
No full textIn recent years, alternative retrofit strategies were developed based on rapid, low-impact, and reversible interventions using external additive structures commonly called exoskeletons, which can be installed without disrupting the facility’s operation. Combining exoskeletons with steel strip dampers (SSDs) offers a sustainable approach, as the SSDs can be replaced after a seismic event. This work presents the design and evaluation of dissipative exoskeletons with SSD-type fuses for the seismic retrofit of reinforced concrete (RC) buildings, using a school building as a case study. The dissipative exoskeletons were designed using a displace-ment-based approach. The effectiveness of the retrofit strategy was demonstrated through nonlinear time-history analyses under different sets of strong earthquake ground motions
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
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