1,720,996 research outputs found
Pedestrian-structure interaction in the vertical direction: coupled model and application to lively footbridges
No full textModel of coordinated crowd dynamics
No full textThis paper presents a mathematical model of synchronisation of multiple people during cyclic activities such as walking, running, jumping and bouncing. Providing that quality models of individual loading for these activities do exist, the sync model is the key component towards an urgently needed yet reliable model of artificial dynamic loading due to multiple active occupants. A model proposed here describes the effect of external and internal factors on the crowd dynamics. The former includes periodic external stimuli on the body motion of individuals, such as perceptible vibration of the ground and music beats. The later addresses the mutual interaction between individuals, such as possibility to see, hear or touch each other. Modelling approach is inspired by the existing models of coupled pendulums while the governing equations feature Mathieu-type behaviour. For the sake of simplicity and efficiency, the model is kept linear and deterministic. All modelling parameters have a physical interpretation and their values can be calibrated to match experimental measurements
Improved model for human induced vibrations of high-frequency floors
Full text linkThis is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordThe key UK design guidelines published by the Concrete Society and Concrete Centre for single human walking excitation of high-frequency floors were introduced more than 10 years ago. The corresponding walking force model is derived using a set of single footfalls recorded on a force plate and it features a deterministic approach which contradicts the stochastic nature of human-induced loading, including intra- and inter- subject variability. This paper presents an improved version of this force model for high-frequency floors with statistically defined parameters derived using a comprehensive database of walking force time histories, comprising multiple successive footfalls that are continuously measured on an instrumented treadmill. The improved model enables probability-based prediction of vibration levels for any probability of non-exceedance, while the existing model allows for vibration prediction related to 75% probability of non-exceedance for design purposes. Moreover, the improved model shifts the suggested cut-off frequency between low- and high-frequency floors from 10 Hz to 14 Hz. This is to account for higher force harmonics that can still induce the resonant vibration response and to avoid possible significant amplification of the vibration response due to the near-resonance effect. Minor effects of near-resonance are taken into account by a damping factor. The performance of the existing and the improved models is compared against numerical simulations carried out using a finite element model of a structure and the treadmill forces. The results show that while the existing model tends to overestimate or underestimate the vibration levels depending on the pacing rate, the new model provides statistically reliable estimations of the vibration responses. Hence, it can be adopted in a new generation of the design guidelines featuring a probabilistic approach to vibration serviceability assessment of high-frequency floors.The authors would like to acknowledge the College of Engineering, Mathematics and Physical Sciences in the University of Exeter for the financial support provided for the PhD programme of the first author. The authors would also like to acknowledge the UK Engineering and Physical Sciences Research (EPSRC) for the following research grants:
Platform Grant EP/G061130/2 (Dynamic performance of large civil engineering structures: an integrated approach to management, design and assessment) and
Standard Grant EP/I029567/1 (Synchronization in dynamic loading due to multiple pedestrians and occupants of vibration-sensitive structures)
Prediction of floor responses to crowd bouncing loads by response reduction factor and spectrum method
No full textBouncing is a typical rhythmic crowd activity in entertaining venues, such as concert halls and stadia. When the activity’s frequency is close to the natural frequency of the occupied structure, the corresponding bouncing loads can cause intense structural vibrations resulting in vibration serviceability problems, even structural damage. This study suggests a method for prediction of vibration response due to crowd bouncing by a response reduction factor (RRF) in conjunction with a previously established response spectrum approach pertinent to a single person bouncing. The RRF is defined as a ratio between structural responses with and without taking into account synchronization of body movements of individuals in a bouncing crowd. The variations of RRF with number of persons, structural frequency, bouncing frequency and structural damping ratios have been studied using experimental records of crowd bouncing loads. Based on the findings a practical design curve for RRF has been proposed. Application of the proposed method has been validated on numerical simulations and field measurements of a long-span floor subjected to crowd bouncing loads
FE modelling and updating of unique fink truss footbridge
No full textRecent improvement of mechanical characteristics of structural materials and fast development of the
finite element (FE) based computational structural analysis are resulting in innovative solutions in
footbridge design. When doing research into dynamic analysis of these structures, their dynamic
properties are required and are usually obtained from an FE model. However, because of structural
complexity, the FE modelling of footbridges is often prone to errors due to modelling uncertainty. The
best and quite often the only way to evaluate the reliability of the FE modelling is to involve modal testing
and FE model updating of footbridge structure with the aim to match test results. Using this approach, a
complex and rather unique Fink truss structure of Royal Victoria Dock Bridge in London was analysed.
Eleven measured modes of vibration were identified via an ambient vibration survey and then compared
with their counterparts from an initial FE model developed by best engineering judgment. In this initial FE
model the maximum difference between two paired natural frequencies was 29%. In a subsequent
updating exercise it was found that uncertainties in main beam and crosshead geometry, as well as the
inherent simplicity of the fully symmetric FE model, were the main source of the modelling error
Vibration performance of a lightweight FRP footbridge under human dynamic excitation
No full textFibre-reinforced polymer (FRP) composites are increasingly used as main load bearing materials in design of pedestrian bridges. The FRP footbridges are typically characterised by high strength, and relatively low mass and stiffness. These properties could lead to excessive vibration response under human-induced dynamic loading. This paper studies dynamic performance of a 19.8 m long, simply supported, FRP footbridge exposed to walking and jogging. Moreover, the vibration response of this bridge is compared and critically evaluated against the response of an equivalent, in terms of natural frequency and span length, composite steel-concrete structure. The main factors that drive the vibration performance of the FRP structure are discussed and some recommendations for vibration serviceability checks are made
Advanced Fourier-based Model of Bouncing Loads
Full text linkThis is the author accepted manuscript. The final version is available from Springer via the DOI in this record36th IMAC, A Conference and Exposition on Structural Dynamics 2018Contemporary design guideline pertinent to vibration serviceability of entertaining venues describes bouncing forces as a deterministic and periodic process presentable via Fourier series. However, fitting the Fourier harmonics to a comprehensive database of individual bouncing force records established in this study showed that such a simplification is far too radical, thus leading to a significant loss of information. Building on the conventional Fourier force model, this study makes the harmonics specific to each individual and takes into account imperfections in the bouncing process. The result is a numerical generator of stochastic bouncing force time histories which represent reliably the experimentally recorded bouncing force signals.The authors would like to acknowledge the financial support provided by PRIN 2015-2018 “Identification and monitoring of complex structural systems” and National Natural Science Foundation of China 347 (51478346) and State Key Laboratory for Disaster Reduction of Civil Engineering (SLDRCE14-B-16)
Statistical characterisation of parameters defining human walking as observed on an indoor passerelle
No full textIncreased slenderness of footbridge structures in the last few decades has led to an
increasing number of vibration serviceability problems under human induced dynamic load,
such as walking. These problems are typically related to increased discomfort of footbridge users
due to perceptible vibrations during footbridge crossing. The current codes of practice dealing
with the vibration serviceability of footbridges often fail to assess reliably the vibration level
induced by humans. This is because they model the load induced by pedestrians by considering
only an ‘average’ walker. However, because of natural diversity in human population, so called
inter-subject variability, it is necessary to model the walking force in a probabilistic way taking
into account this type of variability. To do this, a large database of parameters (such as walking
frequency, step length and weight) describing walking force induced by different individuals is
required. Currently, only limited amount of data to populate this database is available. To generate
more data of this kind, pedestrian traffic on an indoor passerelle inside a University campus
in Sheffield was monitored using video cameras for 6.5 hours. The data that characterise
human walking (such as walking frequency, step length and arrival time) were collected and
analysed statistically. Based on this, the probability density functions for the parameters analysed
were constructed. The results of this study could be used when defining a badly needed
probabilistic force models for vibration serviceability assessment of indoor passerelles of this
kind
Complete statistical approach to modelling variable pedestrian forces induced on rigid surfaces
Full text linkThis study presents a stochastic model of near-periodic walking force signals featuring variable walking speed on the step-by-step basis as the key input modelling parameter. This is a notable departure from traditional deterministic and periodic Fourier series models where the key modelling parameter is the average pacing rate in a walking trial. Walking speed instead of pacing rate is a more natural choice since human nervous system adopts speed of successive steps to the surrounding environment, including vibrations of the supporting structure. Starting from the previously developed models of variable walking speed and spatiotemporal parameters in a walking trial, this study derived a complementary model of variable dynamic loading factors (DLFs) corresponding to the first five dominant harmonics and subharmonics of the walking force. Both the mean and coefficient of variation of DLFs are described as the products of two factors. The first represents the deterministic dependence on the step speed and is modelled as a second-order polynomial. The second factor reproduces the random inter-pedestrian variability of the DLFs which is defined by a Beta distribution. Extensive vibration simulations of virtual footbridges due to measured and simulated walking forces showed a reliable performance of the model. Moreover, the results provided a strong evidence that the step-by-step variability of gait in a single-pedestrian walking trial yields up to 22% relative error in the simulated vibration response
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
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