scholarly journals Quantification of Dynamic Excitation Potential of Pedestrian Population Crossing Footbridges

2011 ◽  
Vol 18 (4) ◽  
pp. 563-577 ◽  
Author(s):  
Stana Žcaronivanović ◽  
Aleksandar Pavić
Keyword(s):  
Real Life ◽  
Vertical Direction ◽  
Design Guidelines ◽  
Vibration Response ◽  
Step Frequency ◽  
Response Level ◽  
Dynamic Excitation ◽  
Excitation Potential ◽  
Vibration Serviceability ◽  
Single Response

Due to their slenderness, many modern footbridges may vibrate significantly under pedestrian traffic. Consequently, the vibration serviceability of these structures under human-induced dynamic loading is becoming their governing design criterion. Many current vibration serviceability design guidelines, concerned with prediction of the vibration in the vertical direction, estimate a single response level that corresponds to an "average" person crossing the bridge with the step frequency that matches a footbridge natural frequency. However, different pedestrians have different dynamic excitation potential, and therefore could generate significantly different vibration response of the bridge structure. This paper aims to quantify this potential by estimating the range of structural vibrations (in the vertical direction) that could be induced by different individuals and the probability of occurrence of any particular vibration level. This is done by introducing the inter- and intra-subject variability in the walking force modelling. The former term refers to inability of a pedestrian to induce an exactly the same force with each step while the latter refers to different forces (in terms of their magnitude, frequency and crossing speed) induced by different people. Both types of variability are modelled using the appropriate probability density functions. The probability distributions were then implemented into a framework procedure for vibration response prediction under a single person excitation. Instead of a single response value obtained using currently available design guidelines, this new framework yields a range of possible acceleration responses induced by different people and a distribution function for these responses. The acceleration ranges estimated are then compared with experimental data from two real-life footbridges. The substantial differences in the dynamic response induced by different people are obtained in both the numerical and the experimental results presented. These results therefore confirm huge variability in different people's dynamic potential to excite the structure. The proposed approach for quantifying this variability could be used as a sound basis for development of new probability-based vibration serviceability assessment procedures for pedestrian bridges.

Evaluation of design requirements for footbridges excited by vertical forces from walking

2001 ◽  
Vol 28 (5) ◽  
pp. 769-777 ◽  
Author(s):  
R L Pimentel ◽  
A Pavic ◽  
P Waldron
Keyword(s):  
Dynamic Loading ◽  
Vertical Direction ◽  
Design Guidelines ◽  
Scientific Data ◽  
Codes Of Practice ◽  
Safety Margins ◽  
Vibration Serviceability ◽  
Factor Evaluation ◽  
Definition Of ◽  
Proper Consideration

The continuing trend towards the design of more slender, lighter, and livelier footbridges has created new challenges that are not properly addressed in a number of widely used codes of practice in Europe and Canada. Recent research into vibration serviceability of slender structures under human-induced dynamic loading suggests that improvements to the existing footbridge design guidelines are possible in the area of modelling human-induced excitation in the vertical direction. This paper evaluates the performance of currently used codes of practice regarding vibration serviceability of footbridges under human-induced loads due to walking. The evaluation is supported by experimental evidence from tests carried out by the authors on potentially lively footbridges. A description of recent research advances is included, together with a comparative analysis of the approaches of some pertinent guidelines used internationally to tackle this design problem. In addition, suggestions are made for re-addressing the problem of vibration serviceability of footbridges by focusing attention on a more realistic definition of vertical pedestrian loading and the corresponding frequency ranges of interest. It was found that the codes are either conservative or lack appropriate safety margins, depending on the frequency range excited by moving pedestrians. This is principally due to the lack of proper consideration for the frequency content of the pedestrian load, which would take into account developments since the 1970s when the scientific data used in the majority of the current codes of practice were produced.Key words: vibration, serviceability, walking, footbridges, design, codes, dynamic loading factor, evaluation.

Development of a Last Stage Blade Row Coupled by Damping Elements: Numerical Assessment of its Vibrational Behavior and its Experimental Validation During Spin Pit Measurements

2017 ◽  
Author(s):  
Christian Siewert ◽  
Frank Sieverding ◽  
William J. McDonald ◽  
Manish Kumar ◽  
James R. McCracken
Keyword(s):  
Structural Integrity ◽  
Mechanical Design ◽  
Vibration Response ◽  
Dynamic Loads ◽  
Steam Turbines ◽  
Response Level ◽  
Vibrational Behavior ◽  
Blade Row ◽  
Calculation Results ◽  
Last Stage

Last stage blade rows of modern low pressure steam turbines are subjected to high static and dynamic loads. The static loads are primarily caused by the centrifugal forces due to the steam turbine’s rotational speed. Dynamic loads can be caused by instationary steam forces, for example. A primary goal in the design of modern and robust blade rows is to prevent High Cycle Fatigue caused by dynamic loads due to synchronous or non-synchronous excitation mechanisms. Therefore, it is important for the mechanical design process to predict the blade row’s vibration response. The vibration response level of a blade row can be limited by means of a damping element coupling concept. Damping elements are loosely assembled into pockets attached to the airfoils. The improvement in the blade row’s structural integrity is the key aspect in the use of a damping element blade coupling concept. In this paper, the vibrational behavior of a last stage blade row with damping elements is analyzed numerically. The calculation results are compared to results obtained from spin pit measurements for this last stage blade row coupled by damping elements.

scholarly journals A Framework for Research in Gamified Mobile Guide Applications using Embodied Conversational Agents (ECAs)

2015 ◽  
Vol 2 (3) ◽  
Author(s):  
Ioannis Doumanis ◽  
Serengul Smith
Keyword(s):  
Real Life ◽  
Design Guidelines ◽  
Location Based Services ◽  
Mobile Technologies ◽  
Conversational Agents ◽  
Cultural Narratives ◽  
Unified Framework ◽  
Research Framework ◽  
Player Experience ◽  
Cognitive Accessibility

Mobile Guides are mobile applications that provide players with local and location-based services (LBS), such as navigation assistance, where and when they need them most. Advances in mobile technologies in recent years have enabled the gamification of these applications, opening up new opportunities to transfer education and culture through game play. However, adding traditional game elements such as PBLs (points, badges, and leaderboards) alone cannot ensure that the intended learning outcomes will be met, as the player’s cognitive resources are shared between the application and the surrounding environment. This distribution of resources prevents players from easily immersing themselves into the educational scenario. Adding artificial conversational characters (ECAs) that simulate the social norms found in real-life human-to-human guide scenarios has the potential to address this problem and improve the player’s experience and learning of cultural narratives [1]. Although significant progress has been made towards creating game-like mobile guides with ECAs ([2], [3]), there is still a lack of a unified framework that enables researchers and practitioners to investigate the potential effects of such applications to players and how to approach the concepts of player experience, cognitive accessibility and usability in this context. This paper presents a theoretically-well supported research framework consisted of four key components: differences in players, different features of the gamified task, aspects of how the ECA looks, sound or behaves and different mobile environments. Furthermore, it provides based on this framework a working definition of what player experience, cognitive accessibility and usability are in the context of game-like mobile guide applications. Finally, a synthesis of the results of six empirical studies conducted within this research framework is discussed and a series of design guidelines for the effective gamification of mobile guide applications using ECAs are presented. Results show that an ECA can positively affect the quality of the player’s experience, but it did not elicit better player retention of cultural narratives and navigation of routes.

scholarly journals Assessment of the Lateral Vibration Serviceability Limit State of Slender Footbridges Including the Postlock-in Behaviour

2020 ◽  
Vol 10 (3) ◽  
pp. 967 ◽  
Author(s):  
Rocío G. Cuevas ◽  
Javier F. Jiménez-Alonso ◽  
Francisco Martínez ◽  
Iván M. Díaz
Keyword(s):  
Limit State ◽  
Sudden Onset ◽  
Design Guidelines ◽  
Comfort Level ◽  
Lateral Vibration ◽  
Vibration Serviceability ◽  
Current Design ◽  
Common Criterion ◽  
Lock In Effect ◽  
Lock In

The lateral vibration serviceability of slender footbridges has been the subject of many studies over the last few decades. However, in spite of the large amount of research, a common criterion has not been set yet. Although the human–structure interaction phenomenon is widely accepted as the main cause of the sudden onset of high amplitudes of vibration, the current design recommendations do not include an expression for the auto-induced component of the pedestrian action and, as a consequence, it is not possible to evaluate the footbridge comfort once the lock-in effect has developed. Hence, the purpose of this paper is to propose a general formulation, which allows the analysis of the different load scenarios that the footbridge will experience during its overall life cycle. An important advantage over most current design guidelines is that the procedure permits the evaluation of the comfort level of the footbridge, even with crowd densities above the “critical number”, and thus takes informed decisions about the possible use of external devices to control the vibration response, depending on the probability of occurrence of the problem. The performance of the proposed method is successfully evaluated through numerical response simulations of two real footbridges, showing a good agreement with the experimental data.

Experimental Investigations of Single and Multi-Fault in Rotor System

2014 ◽  
Vol 541-542 ◽  
pp. 628-634
Author(s):  
S.P. Mogal ◽  
D.I. Lalwani
Keyword(s):  
Fourier Transform ◽  
Fast Fourier Transform ◽  
Real Life ◽  
Rotor System ◽  
Vibration Response ◽  
Experimental Investigations ◽  
Multiple Faults ◽  
Single Fault ◽  
Vibration Behavior ◽  
Combined Action

Many researchers dealt with single fault but in real life situations, combined action of two or more single faults are usually present. Multi-faults (two and three combinations) were studied by few researchers. Researchers have mostly studied the vibration behavior of a rotor with misalignment, unbalance and rub separately. This paper presents one such case, where multiple faults are considered together in a rotor system, i.e. misalignment, unbalance and rub. The objective of this paper is to experimentally investigate the vibration response of combined of three faults misalignment, unbalance and rub using Fast Fourier Transform (FFT). FFT spectrum of combination of three faults misalignment, unbalance and rub show 1 X and 2 X are predominant and many sub harmonics are generated.1X peak represent unbalance, 2X peak represents misalignment and sub harmonics shows rub fault.

Numerical and Experimental Study on the Dynamic Behavior of an Innovative Steel-Concrete Composite Hollow Waffle Floor

2020 ◽  
Vol 20 (08) ◽  
pp. 2050087
Author(s):  
Xi Zhang ◽  
Qing Li ◽  
Yousan Wang ◽  
Qiming Wang
Keyword(s):  
Experimental Study ◽  
Structural Parameters ◽  
Design Guidelines ◽  
Element Analysis ◽  
Long Span ◽  
Vibration Serviceability ◽  
Floor Vibration ◽  
Walking Tests ◽  
Vibration Performance ◽  
Hollow Beams

The U-shaped steel-concrete composite hollow waffle (CHW) floor is an innovative slender large-span floor composed of a thin slab and bidirectional orthogonal steel-concrete composite hollow beams. Large vibrations may occur under human excitations, and vibration guidelines for CHW floors are still lacking. Thus, this paper undertook a parametric and experimental study to explore the vibration performance of the CHW floors. First, the modal properties and vibration response under walking tests considering the varying frequencies and routes were obtained from the measurements, which validated the accuracy of the finite element analysis (FEA). Then, the influence of the structural parameters on the floor vibration was investigated by numerical modeling. The parametric study shows that the medium-sized long-span (MLS) (28[Formula: see text]m) CHW floors present the best vibration serviceability, the small-sized long-span (SLS) (14[Formula: see text]m) CHW floors vibrate substantially under walking excitation, and the large-sized long-span (LLS) (42[Formula: see text]m) CHW floors are vulnerable to resonance. Finally, this paper provides recommendations for design guidelines for CHW floors and indicates that controlling the span-to-height (SH) value and beam spacing (BS) at a small value are the most effective methods of vibration control.

scholarly journals Vibration serviceability assessment of office floors for realistic walking and floor layout scenarios: Literature review

2019 ◽  
Vol 23 (6) ◽  
pp. 1238-1255
Author(s):  
Márcio S Gonçalves ◽  
Aleksandar Pavic ◽  
Roberto L Pimentel
Keyword(s):  
Design Guidelines ◽  
Design Criterion ◽  
Embodied Energy ◽  
Human Gait ◽  
Vibration Source ◽  
Structural Elements ◽  
Single Person ◽  
Vibration Serviceability ◽  
Floor Vibration ◽  
Vibration Performance

Over the last two decades, office floors have been built progressively lightweight with increasing spans and slenderness. Therefore, vibration performance of office floors due to walking dynamic loads is becoming their governing design criterion, determining their size and shape, and therefore overall weight and embodied energy of the building. To date, floor design guidelines around the world recommend walking load scenarios in offices featuring some or all of the following standard characteristics: (a) walking loads are assumed to be periodic dynamic excitation represented by the Fourier series, including harmonics corresponding to up to the first four integer multiples of the pacing frequency of which at least one is exciting the floor at a resonant frequency and (b) single person walking. However, the literature surveyed provides evidence that such assessment methodology is potentially an over-simplification which does not reflect real walking load scenarios, since crucial features of the floor vibration source, path and receiver are missing. First, in terms of vibration source, realistic scenarios need to feature (a) moving rather than stationary walking forces, (b) stochastic nature of human gait, (c) simultaneous multi-person walking and (d) human–structure interaction. Second, for the transmission path (i.e. office floor structure), two features are needed to consider: (a) realistic office floor layouts and (b) presence, or absence, of non-structural elements. Finally, for the vibration receivers (i.e. floor occupants), (a) vibrations calculated at floor locations occupied by users (instead of at the potential highest response location which may not be occupied), (b) actual period over which occupants feel vibration due to such excitation and (c) assessment of vibration levels based on their probability of occurrence. This study therefore addresses these seldom considered but increasingly important features and discusses realistic approaches to floor design for vibration serviceability.

Analogies Between Coupled-Mode Gate Vibration and Coupled-Mode Flutter

2017 ◽  
pp. 565-592
Keyword(s):  
Design Guidelines ◽  
Frequency Mode ◽  
Suspension Bridges ◽  
Two Dimensional ◽  
Mode Instability ◽  
Dynamic Design ◽  
Coupled Mode ◽  
Dynamic Excitation ◽  
Bridge Failure ◽  
Tacoma Narrows Bridge

In this chapter the similarities between the Tacoma Narrows Bridge failure in 1940 and the Folsom Dam gate failure in 1995 are examined. In both cases, static design guidelines were followed in the design of the structure under the assumption that large, massive structures would not be susceptible to dynamic excitation. Fundamentals of two-dimensional coupled mode flutter are presented. The frequency mode coalescence that occurs in two-dimensional flutter is noted. It is seen to have some resemblance to the mode-coupling in the coupled-mode instability of Tainter gate. The need for development of dynamic design guidelines for Tainter gates is argued to be parallel to the need for dynamic design guidelines for suspension bridges in the wake of the Tacoma Narrows failure.

Vibration Analysis of Steam Generators and Heat Exchangers: An Overview — Part II: Vibration, Response, Fretting-Wear, Guidelines

2002 ◽  
Author(s):  
Michel J. Pettigrew ◽  
Colette E. Taylor
Keyword(s):  
Heat Exchangers ◽  
Vibration Analysis ◽  
Response Prediction ◽  
Design Guidelines ◽  
Vibration Response ◽  
Fretting Wear ◽  
Steam Generators ◽  
Flow Induced Vibration ◽  
Two Phase ◽  
Service Water

Design guidelines were developed to prevent tube failures due to excessive flow-induced vibration in shell-and-tube heat exchangers. An overview of vibration analysis procedures and recommended design guidelines is presented in this paper. This paper pertains to liquid, gas and two-phase heat exchangers such as nuclear steam generators, reboilers, coolers, service water heat exchangers, condensers, and moisture-separator-reheaters. Part 2 of this paper covers forced vibration excitation mechanisms, vibration response prediction, resulting damage assessment, and acceptance criteria.

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