1,721,070 research outputs found
Mathematical model to generate asymmetric pulses due to human jumping
No full textA novel mathematical modeling has been proposed to generate synthetic vertical force signal induced by a single person jumping. This model can replicate much of the temporal and spectral features of the real jumping loading more reliably than the existing half-sine models coupled with Fourier series analysis. This includes lack of symmetry of individual jumping pulses and near-periodic nature of consecutive pulses. The model therefore offers way forward as to the development of a new generation of synthetic narrow-band jumping loads. In these, the shape and frequency content of the jumping force can be changed easily on a jump-by-jump basis, which simulates better on what is happening in reality during human jumping. The synthetic jumping loading can be used in assessing vibration serviceability of civil engineering structures for which such dynamic excitation is relevant, such as assembly structures and concert venues
Mathematical model to generate near-periodic human jumping force signals
No full textA mathematical modelling procedure has been developed to generate synthetic vertical force signals induced by a single person jumping. The ability to replicate much of the temporal and spectral features of real jumping loads give this model a definite advantage over the conventional half-sine models coupled with Fourier series analysis. This includes modelling of the omnipresent lack of symmetry of individual jumping pulses and jump-by-jump variations in amplitudes and timing. The model therefore belongs to a new generation of synthetic narrowband jumping loads that simulate reality better. The proposed mathematical concept for characterisation of irregular jumping pulses may be utilised in vibration serviceability assessment of civil engineering assembly structures, such as grandstands, footbridges and concert or gym floors, to estimate realistic dynamic structural response due to people jumping. (C) 2009 Elsevier Ltd. All rights reserved
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)
Vibration serviceability of long-span cast in-situ concrete floors.
Full text linkThis thesis describes an investigation into the vibration serviceability of long-span and slender in-situ concrete floors, which are typically post-tensioned. The motivation for the research is the present trend towards increased slenderness of post-tensioned floors supporting open-plan high- quality offices where vibration serviceability may easily become the governing design criterion. The vibration serviceability issue in post-tensioned floors is now also recognised by the UK Concrete Society which proposed, for the first time, guidelines for performing a vibration serviceability check when designing office floors. The guidelines were published in Concrete Society Technical Report 43 (CSTR43) in 1994 and its publication prompted the initialisation of this research project. There were two reasons for this. Firstly, problems were reported with the reliability and practical application of these guidelines, and, secondly, the guidelines were not experimentally verified which is unusual for any design provision related to vibration serviceability. In order to improve understanding of the dynamic performance of a rather specific group of office floors which are long-span and made of cast in-situ concrete, a combined experimental and analytical approach has been adopted. A state-of-the-art facility comprising hardware and software suitable for field modal testing and dynamic response measurements of prototype floor structures was commissioned as a part of this research. The facility is built up around the instrumented sledge hammer, which served as the main excitation source in modal testing, and multi-degree-of-freedom vibration parameter estimation procedures utilising measured floor frequency response functions. The main testing programme consisted of modal testing of four prototype floor structures of varying complexity weighing between 13 and 1000 tonnes. All four slab structures were slender and made of in-situ concrete. These tests were complemented by measurements of the floors' acceleration responses to a single person walking excitation tuned to create as large as realistically possible responses. The modal testing experimental data (measured natural frequencies, mode shapes and modal damping ratios) were used to validate numerical finite element (FE) models representing each floor structure. To do this, advanced FE model correlation and manual updating procedures were employed. Results of these exercises highlighted a number of important issues related to the dynamic behaviour of the concrete floors investigated. Firstly, the bending stiffness of in-situ concrete columns and walls contributed significantly to overall floor bending stiffness and must be considered. Secondly, higher modes of vibration which are close to the fundamental frequency appear in concrete floors, and should not be neglected as they can be easily excited by walking leading to dynamic responses greater than those associated with the fundamental mode. Thirdly, the width of band beams contributes significantly to the lateral stiffness of post-tensioned floors, which, in turn, may be very beneficial for their vibration serviceability. The validated numerical FE models were then used to check the performance of three representative walking excitation models available in the literature. It was shown that, in general, all three models overestimated the measured response to the third harmonic of the walking excitation, which is particularly important for low-frequency office floors. Only one of the models did so in a way which is not overly conservative. This model is recommended for use in vibration serviceability assessment of post-tensioned floors. Finally, gross oversimplification of these important issues is identified as the principal reason for the failure of the current CSTR43 vibration serviceability guidelines to predict reliably vibration response of a wide range of post-tensioned in-situ cast concrete floors
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)
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
Stochastic approach to modelling of near-periodic jumping loads
No full textA mathematical model has been developed to generate stochastic synthetic vertical force signals induced by a single person jumping. The model is based on a unique database of experimentally measured individual jumping loads which has the most extensive range of possible jumping frequencies. The ability to replicate many of the temporal and spectral features of real jumping loads gives this model a definite advantage over the conventional half-sine models coupled with Fourier series analysis. This includes modelling of the omnipresent lack of symmetry of individual jumping pulses and jump-by-jump variations in amplitudes and timing The model therefore belongs to a new generation of synthetic narrow band jumping loads which simulate reality better. The proposed mathematical concept for characterisation of near-periodic jumping pulses may be utilised in vibration serviceability assessment of civil engineering assembly structures, such as grandstands, spectator galleries, footbridges and concert or gym floors, to estimate more realistically dynamic structural response due to people jumping
Improved footfall model for vibration of high-frequency floors
No full textHuman induced vibration is one of the essential design considerations for the design of high-frequency building floors supporting vibration sensitive equipment and processes, such as precision laboratories and operating theatres in hospitals. For this purpose, the model derived by Arup, and adopted by the current UK Concrete Society and the Concrete Centre design guidelines, has been widely used. In this paper, the same model was derived again using more realistic and statistically more reliable walking forces measurements than those used to derive the original model. These forces, which comprise more than 50,000 single footfall forces, were previously measured from more than 70 participants walking on a treadmill. By comparing Arup’s effective impulse equation: Ieff = 54(fp1.43/ fn1.3) by the derived effective impulse: Ieff = 275(fp1.22/ fn1.74), a clear difference between the two models can be noticed and this indicates the importance of using more realistic walking forces to derive the model. This could be achieved by deriving this model using continuously measured walking forces from statistically sufficient number of people
Data-driven model of random lateral pedestrian excitation
No full textPublishedRandomness and narrow band nature are the two essential features of lateral walking loading not addressed adequately in the existing design guidelines for footbridges. One of the reasons for this is the lack of a comprehensive database of lateralwalking forces in the formof continuously recorded time series that can be used for development of statistically reliable characterisation of these forces for application in the civil engineering context. This paper has addressed the issue by establishing a large database of measured lateral walking time series recorded by a state-of-the-art instrumented treadmill at the University of Sheffield. Another reason is the lack of an adequate modelling strategy which can simulate reliably the actual forcing records. Motivated by the existing models of wind and earthquake loading, speech recognition techniques and a method of replicating electrocardiogram (ECG) signals, a data-driven mathematical model has been developed to generate synthetic force signals with realistic temporal and spectral features. This multi-disciplinary modelling strategy offers a radical departure from traditional Fourier-based representations of lateral walking loads towards more reliable and more realistic vibration serviceability assessment of footbridges. © 2013 Taylor & Francis Group, London, UK.The authors would like to acknowledge the financial
support provided by the UK Engineering and
Physical Sciences Research Council (EPSRC) for
grant reference EP/E018734/1 (“Human Walking and
Running Forces: Novel Experimental Characterisation
and Application in Civil Engineering Dynamics”) and
to thank all test subjects for participating in the data
collection
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
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