1,720,967 research outputs found
Sensitivity analysis of coupled crowd-structure system dynamics to walking crowd properties
No full textIncreasing vibration serviceability problems of modern structures have drawn researchers' attention to the walking-induced vibration modelling and assessment of floors and footbridges. Changes of dynamic properties of structure due to presence of stationary people have been studied extensively in the literature. However, little is known about the similar effects of walking people, mainly due to the lack of experimental evidence and credible models capable of simulating human-structure dynamic interaction (HSI) in the vertical direction. This paper uses a single degree of freedom mass-spring-damper (MSD) model to simulate dynamics of walking crowd on structure and investigates the sensitivity of the coupled crowd-structure system frequency and damping to properties of crowd model. Results of this study show that when the natural frequency of the crowd model is less than the natural frequency of the structure, both natural frequency and damping ratio of occupied structure are more sensitive to crowd's model stiffness. Similarly, when the natural frequency of the crowd model is greater than the natural frequency of the structure, both natural frequency and damping ratio of occupied structure are more sensitive to crowd's model mass. It also can be seen that natural frequency of theoccupied structure has no sensitivity to damping of the crowd model while its damping ratio shows a limited sensitivity to the crowd's model damping with the maximum where both natural frequencies are equal. © 2013 Taylor & Francis Group, London, UK
Effect of group walking traffic on dynamic properties of pedestrian structures
Full text linkThe increasing number of reported vibration serviceability problems in newly built pedestrian structures, such as footbridges and floors, under walking load has attracted considerable attention in the civil engineering community over the past two decades. The key design challenges are: the inter- and intra-subject variability of walking people, the unknown mechanisms of their interaction with the vibrating walking surfaces and the synchronisation between individuals in a group. Ignoring all or some of these factors makes the current design methods an inconsistent approximation of reality. This often leads to considerable over- or under-estimation of the structural response, yielding an unreliable assessment of vibration performance
Paradigm shift in structural vibration serviceability: New assessment framework based on human’s experience of vibration
No full textReliable assessment of structural vibration serviceability during the design process is still a great challenge for the designers of pedestrian structures, such as footbridges and floors. Witness to this is the report of the UK Institution of Structural Engineers that approximately half of its 27,000 members, worldwide, have dealt with vibration serviceability complains related to the code-compliant designs. Although structures are meant to be designed to provide function/comfort for human users, evaluation of the ‘experience’ of the human users is conspicuously absent from structural design guidelines. This paper highlights the distinctive features of the Interaction-based Vibration Serviceability Assessment (I-VSA) method, proposed by the authors, and compares the results of the I-VSA with those of the current guidelines for two full-scale structures. It further proposes that: (1) the level of vibrations received by human users is a significantly more informative design parameter than maximum response levels at a certain locating on the structure, which may or may not be experienced; and (2) a deep understanding of the ‘perception’ of vibration by humans is needed to link the level of vibrations received by the occupants with their ‘experience’ from this vibration
Using MSD model to simulate human-structure interaction during walking
No full textIncreasing vibration serviceability problems of modern pedestrian structures have drawn researchers' attention to detailed modelling and assessment of walking-induced vibration on floors and footbridges. Stochastic nature of human walking and unknown mechanisms of their interaction with the structure and surrounding environment, make it difficult to simulate. Ignoring these complexities has rendered the current design methods to a rough approximation of reality which often leads to considerable over or under-estimalion of the structural response yielding unreliable assessment of vibration performance. Some aspects of human-structure interaction (HSI), such as synchronization, have been studied extensively, mostly in the lateral direction. But, despite of its much bigger significance, effects of walking pedestrians on dynamic properties of structures in the vertical direction are mostly ignored. This is mainly due to the lack of credible HSI experimental data in the vertical direction as well as models capable of simulating the interactions between the two dynamic systems. To address this gap, this paper tries to adapt a classic single degree of freedom mass-spring-damper (MSD) model of human body to illustrate the effects of walking pedestrians on dynamic properties of structures. Parametric studies were carried out to analyse effects of the human model dynamic properties on coupled system response. This MSD model can be seen as the basic building block of realistic human body models which are currently being developed to address both biomechanical specifics and HSI effects on structures occupied and excited by walking human
Identification of mass–spring–damper model of walking humans
Full text linkInteraction of walking people with vibrating structures is known to be an important yet challenging phenomenon to simulate. Despite of its considerable effects on the structural response, no properly formulated and experimentally verified model currently exists to simulate this interaction in the vertical direction.
This work uses a single-degree-of-freedom mass–spring–damper model of a walking human to simulate its interaction with a vibrating structure. Extensive frequency response function measurements were performed on a test structure that was occupied by more than a hundred test subjects walking in various group sizes and at different times in 23 tests. The identified modal properties of the occupied structure were used in three different identification procedures to estimate the parameters of the walking human model.
A discrete model of human–structure system was used to simulate interaction of each walking person with the structure. The analysis identified the range of 2.75–3.00 Hz for the natural frequency and 27.5%–30% for the damping ratio of the model of a walking human, having constant mass of 70 kg. The extent of the experimental data and the measurement details, diversity of loading scenarios and consistency of the results of the different identification procedures, provided high level of confidence on the suggested parameters for the single-degree-of-freedom walking human model.UK Engineering and Physical Sciences Research Council (EPSRC
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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