1,721,030 research outputs found
Pedestrian-Footbridge Dynamic Interaction: A Probabilistic Assessment of Vibration Serviceability
Full text linkRecent footbridges are characterized by long span, light materials and increasing slenderness, which make them more sensitive to dynamic forces induced by pedestrians. The vibration serviceability under human-induced dynamic forces is the governing criterion for the design of these slender structures. To assess serviceability, the bridge response must be computed accounting for human-structure interaction, adopting reliable estimates of expected loading scenarios, accurate models representing pedestrians and suitable integration techni¬ques. The present contribution investigates the dynamic response of a lively footbridge due to a group of pedestrians described as bipedal mechanical systems able to reproduce the human gait. Based on a numerical procedure previously developed, extensive simulation activity is performed in order to characterize the structural response in a probabilistic way. The step frequencies of the pedestrians are considered as correlated random variables, where correlation is based on mutual distance among pedestrians
Experimental and numerical serviceability assessment of a steel suspension footbridge
Full text linkThe paper summarizes the main results of the serviceability assessment of a steel suspension footbridge, performed through dynamic testing and numerical simulations. The experimental part of the study involved both operational modal testing and measurement of the structural response under the crossing of different groups of pedestrians. The footbridge exhibited quite complex dynamic characteristics (i.e. two couples of closely spaced modes and five modes in the frequency range 1.9–3.0 Hz) and the maximum accelerations induced by pedestrians and joggers turned out to be in the range of discomfort. An accurate FE model, based on the design drawings, was then developed and a general procedure is proposed to tackle the crucial issue of assigning the design tension forces to the suspension elements. Since the comparison between numerical and experimental results generally shows a good agreement, the model is adopted to perform a numerical assessment of vibration serviceability according to the European guideline HiVoSS. A minor shortcoming of HiVoSS and the unusual relevance of the 2nd harmonic of pedestrian-induced load are highlighted for the investigated footbridge
Vibration testing and FE modelling oF a lively footbridge
No full textThe paper focuses on the results of dynamic testing and numerical simulation of a suspension footbridge. The experimental part of the study involved both operational modal testing and measurement of the structural response under the crossing of the footbridge by different groups of pedestrians. The footbridge exhibited quite complex dynamic characteristics (i.e. closely spaced modes and 5 modes in the frequency range 2-3 Hz) and the maximum vertical accelerations induced by pedestrians and joggers turned out to be in the range of discomfort. The investigation was completed by the development of a numerical FE model (based on the design data), with the twofold objective of reproducing the observed dynamic characteristics and simulating the dynamic interaction pedestrians-structure
A MSD model for coupled analysis of pedestrian-footbridge dynamic interaction
Full text linkRecent footbridges are characterized by long span, light materials and increasing slenderness which make them more sensitive to dynamic forces induced by pedestrians. While walking, the pedestrian adapts his gait to the bridge motion and interacts with the structure. At contact points, the pedestrian transmits contact forces to the bridge that, in turn, imposes a set of displacements and velocities to the pedestrian's feet. The bridge response accounting for the human-structure interaction depends both on reliable estimates of expected loading scenarios and on the accuracy of the models representing pedestrians.This work presents a complete framework for the analysis of the human-structure dynamic interaction. To properly describe this phenomenon, the coupled equations of motion for the two mechanical systems are derived. To this aim the standard FE modeling of the structure is retained, while a new bipedal mass-spring-damper model is adopted for the pedestrian. The model is able to reproduce the sequence of single and double support phases typical of the human gait and is excited by both an equivalent bio-mechanical force and the motion at contact points with the bridge. The solution of the coupled formulation is based on a forced uncoupling of the equations, possibly associated to an iterative integration procedure. At each time instant the two systems are analyzed separately: the bridge subjected to vertical contact forces, the pedestrian to an imposed motion at his feet.The uncoupled strategy of solution is implemented into a research code. In the case study groups of pedestrians cross a lively footbridge, whose modal properties were experimentally identified. The numerical model was developed with ANSYS. To investigate the potential of the proposed approach, numerical analyses have addressed the effect on the bridge response of both the degree of synchronization and the spatial distribution of groups of nine pedestrians. The bridge vertical accelerations reach values out of the range of comfort and show an high dependency on these parameters. The effectiveness of the proposed approach of modeling and analysis is highlighted. (C) 2017 The Authors. Published by Elsevier Ltd
Uncoupled approaches for walking-induced vertical vibration of a lively footbridge
Full text linkThe recent trend towards the design of flexible footbridges, characterized by a low ratio between permanent and variable load, has made them more sensitive to dynamic forces induced by pedestrians. While walking, the pedestrian moves on the flexible structure adapting his gait to the bridge motion and interacting with the footbridge. At contact points, the pedestrian transmits contact forces to the bridge that, in turn, imposes a set of displacements and velocities to the pedestrian’s feet. The pedestrian is here described with an increasing accuracy. Neglecting the interaction with the bridge, the pedestrian is described with a refined force model, that simulates the force pattern transmitted by each foot. The position of the two forces reproduces the sequence of single and double support phases, typical of the human gait. Interaction is accounted for when both systems are described as mechanical systems (having proper mass, stiffness and damping matrices). In this work a newly proposed bipedal pedestrian mass-spring-damper model is adopted, sharing with the force model the same type of locomotion. The mechanical system is excited by an equivalent bio-mechanical force and its equation of motion takes into account the interaction with the bridge. The coupled equations of motion of the bridge-pedestrian system are then derived; with a forced uncoupling of the equations, the two systems can be analyzed separately. The case study concerns a lively footbridge, whose dynamic response is computed with the different modeling approaches
Prevalence of Mood Disorders in a university students population
No full textTo evaluate (i) the incidence of psychiatric disorders and (ii) the frequency of Mood Disorders diagnoses in a sample of 115 university students afferent to Sportello Counseling-Accoglienza Studenti "Fatti vivo!" of "Sapienza" University of Rome, between November 2008 and December 2010; to point out correlations with socio-demographic variables. The prevalence of Mood Disorders was evaluated with the Structured Clinical Interview for DSM IV Axis I Disorders Clinical Version (SCID-I cv), drawn up by the counselor at first meeting. Each student completed a data collection from which investigates socio-demographic characteristics. A descriptive analysis was conducted and the associations between variables and Axis I diagnoses were investigated. The overall mean age is 24.7 years. A DSM IV-TR Axis I Disorder was diagnosed in 26.9%, of which 45.2% is constituted by Mood Disorders (mean age of 25.7 years). Male students, the highest family members' mean age and the lowest regular studies (64% pursue a course of regular studies) seem to be characteristics of the subgroup of students with Mood Disorders diagnoses compared to the subgroups with other Axis I Disorders diagnoses. Moreover, the same subgroup most frequently recognizes as pathological its condition (78.6%) compared to the subgroup with other Axis I Disorders diagnoses (53.3%). Those differences, however, aren't statistically significant. The discovered percentage of Axis I diagnoses in general and Mood Disorders in particular could be considered representative of perceived unease degree in a population of university students. At the same time, the difficulty in identifying the early signs of uneasiness and in recognizing as pathological own condition interferes with and delays the awareness of the need of a psychological/psychiatric support and the expression of the help-seek
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
Walking-induced vibration of a footbridge
Full text linkIn the last years, the need for structures able to link the functional and aesthetic role has led engineers and architects to design footbridges characterized by long span, light materials and increasing slenderness. The low ratio between permanent and variable loads makes recent footbridges more sensitive to the dynamic loads, such as the forces transmitted by pedestrian. Excessive vibrations may arise when the bridge natural frequencies are very close to those characterizing the human activities: walking, jogging and running. This issue became relevant after the Millenium Bridge inauguration, when an excessive lateral sway motion was triggered by the synchronization between bridge and pedestrian movements. The dynamic behavior of a lively footbridge over-passing the Serio river near Seriate (about 50 km far from Milan), Italy, is investigated in this paper. The suspension bridge, 63.75 m long, is composed of a timber deck on a steel grid. The footbridge model, based on the as-built design data, is implemented in the ANSYS framework. The numerical frequencies computed through the FE model match those identified from the results of the experimental campaign of ambient vibration measurements in a fully satisfactory way. Since the bridge displays several frequencies in the range excited by human activities, its response to crossing pedestrians is investigated. The dynamic interaction pedestrians-footbridge is analyzed for different classes of traffic with two approaches. First, the FE model developed in ANSYS is excited by the distributed harmonic load model for a pedestrian stream, applied on the bridge coherently with the corresponding mode shape, as suggested by the Hivoss Guideline. Second, an ad-hoc developed numerical code is adopted to compute the bridge dynamic response to moving forces. This code reads as input data the structural matrices computed in ANSYS and integrates the equations of motion of a system in which the pedestrian is modeled as a constant vertical travelling force along the footbridge deck. The vibration serviceability under the vertical component of pedestrian load is assessed by comparison to comfort criteria. The results of the Hivoss guideline show accelerations exceeding the value of comfort. The transient analysis predicts lower values within the limits. The two sets of values can be interpreted as an upper and lower bound of the actual response
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