New Vibration Online Journal Will Get Us Back to Basics

This is the final version of the article. Available from MDPI via the DOI in this record.When Vibration approached me to be its founding Editor-in-Chief, it was explained to me that the key selling points of this new online journal would be as follows [...

Effect of Walking people on Dynamic Properties of Floors

This is the final version of the article. Available from Elsevier via the DOI in this record.X International Conference on Structural Dynamics, EURODYN 2017Despite the intensive research that has focused on the dynamic interaction between walking people and slender footbridges, this phenomenon has never been investigated for floor structures. For lightweight floors having mass of 150 kg/m2 or less, where they have relatively low modal masses and damping ratios, this interaction is expected to be more effective than that for normal floors. Such phenomenon, if proven to exist for floors, could explain one of the reasons behind the discrepancy between the measured vibration response of floors due to human walking and the corresponding predicted responses using the currently available models which neglect human-structure interaction for walking humans. This paper presents the first attempt to investigate the effect of walking people on the dynamic properties of floors. It is based on several experimental tests for groups of people walking on a full-scale but slender laboratory floor structure. For each experiment, a modal test was carried out to identify the dynamic properties of the tested floor. The results showed a significant increase in modal damping for the first vibration mode, while higher modes exhibited less damping increase. A slight increase was also noticed in the natural frequency of the observed modes. These changes in the modal properties are in line with previous observations of the effects of walking people on footbridges. The results presented in this paper can pave the way for future research to model the interaction between walking people and the supporting floor structures in the context of their vibration serviceability.The authors are grateful for the College of Engineering, Mathematics and Physical Sciences in the University of Exeter for the financial support they provided for the first author and his PhD program. The authors would also like to acknowledge the financial support provided by the UK Engineering and Physical Sciences Research Council (EPSRC) for grant reference EP/K03877X/1 ('Modelling complex and partially identified engineering problems - Application to the individualised multiscale simulation of the musculoskeletal system')

Simulation of people’s movements on floors using social force model

This is the author accepted manuscript. The final version is available via the link in this recordVibration serviceability assessment of floors has been traditionally based on a scenario of a single person walking along a path which will generate maximum vibration level. This is due to the difficulty of predicting the real positions and paths of the walking people. With such a design scenario, it is possible to obtain calculated responses, which could be both over- or underestimated, depending on the specifics. This could be due to considering only one person walking along one walking path in the simulations. This aspect in the design guidelines could be improved if realistic modelling of people’s movements is utilised. Hence, this paper examines the performance of the social force model to simulate the behaviour of people’s movements on floors. This method has been widely used to model a crowd of people in evacuation and panic situations. However, it has been reported in the literature that this approach could be used to model people’s movements in normal situations as well. The simulation carried out in this paper focuses on the interaction between walking people themselves and between walking people and the surrounding boundaries in typical office floors. The results show that reasonable and realistic behaviour of the floor occupants could be obtained using the social force model. Furthermore, utilising the ‘heatmap’ can help the designers to visualise and obtain information about the proportion of time spent by walking individuals at various points on the floor. This approach can be adopted in a more realistic procedure for the vibration serviceability assessment of floorsEngineering and Physical Sciences Research Council (EPSRC)University of Exete

Utilising an advanced technology of people tracking in vibration serviceability application

This is the author accepted manuscript. The final version is available from Springer via the DOI in this recordEVACES 2017 - 7th International Conference on Experimental Vibration Analysis for Civil Engineering Structures, San Diego, USA, 12-14 July 2017There is a continuous development in the facilities used for experimental measurements of human-induced vibrations due to walking of people in real-life structures. These facilities can be classified into three categories: 1. systems used to measure walking forces, 2. systems used to measure structural dynamic properties and vibration responses and 3. equipment required to locate the position of people within the structure. In recent years, state-of-the-art technologies have enabled both direct and indirect measurement of walking forces and vibration responses with improved accuracy. However, determining people’s position on the structure they occupy and dynamically excite is still a challenge, despite its importance. This is due to the limitations and lack of accuracy of existing systems used for this purpose. This paper presents an advanced system based on the Ultra-WideBand (UWB) technology to track the position of multiple people within civil engineering structures. It is demonstrated that this system has the capability of providing measurements of people’s positions in real-time, with around 50 cm accuracy, using wearable compact tags. In addition to the accuracy, the simple setting up and capability to track people’s positions in different types of structures are advantages over other types of body location tracking systems. Incorporating the above mentioned systems to measure simultaneously walking-induced forces, realistic time-varying locations of these forces and the corresponding time-varying vibration responses has created an unprecedented opportunity to boost considerably research pertinent to human-induced vibration. This will be based on invaluable but, until now, difficult to conduct real-life simultaneous measurements of these three key time-varying walkingforce parameters.The authors are grateful for the College of Engineering, Mathematics and Physical Sciences in the University of Exeter for the financial support they provided for the first author and his PhD program. The authors would also like to acknowledge the financial support provided by the UK Engineering and Physical Sciences Research Council (EPSRC) for grant reference EP/K03877X/1 ('Modelling complex and partially identified engineering problems- Application to the individualised multiscale simulation of the musculoskeletal system')

Simulation of people’s movements on floors using social force model

This is the author accepted manuscript. The final version is available via the link in this recordVibration serviceability assessment of floors has been traditionally based on a scenario of a single person walking along a path which will generate maximum vibration level. This is due to the difficulty of predicting the real positions and paths of the walking people. With such a design scenario, it is possible to obtain calculated responses, which could be both over- or underestimated, depending on the specifics. This could be due to considering only one person walking along one walking path in the simulations. This aspect in the design guidelines could be improved if realistic modelling of people’s movements is utilised. Hence, this paper examines the performance of the social force model to simulate the behaviour of people’s movements on floors. This method has been widely used to model a crowd of people in evacuation and panic situations. However, it has been reported in the literature that this approach could be used to model people’s movements in normal situations as well. The simulation carried out in this paper focuses on the interaction between walking people themselves and between walking people and the surrounding boundaries in typical office floors. The results show that reasonable and realistic behaviour of the floor occupants could be obtained using the social force model. Furthermore, utilising the ‘heatmap’ can help the designers to visualise and obtain information about the proportion of time spent by walking individuals at various points on the floor. This approach can be adopted in a more realistic procedure for the vibration serviceability assessment of floorsEngineering and Physical Sciences Research Council (EPSRC)University of Exete

Estimation of tri-axial walking ground reaction forces of left and right foot from total forces in real-life environments

This is the final version of the article. Available from MDPI via the DOI in this record.Continuous monitoring of natural human gait in real-life environments is essential in many applications including disease monitoring, rehabilitation, and professional sports. Wearable inertial measurement units are successfully used to measure body kinematics in real-life environments and to estimate total walking ground reaction forces GRF(t) using equations of motion. However, for inverse dynamics and clinical gait analysis, the GRF(t) of each foot is required separately. Using an experimental dataset of 1243 tri-axial separate-foot GRF(t) time histories measured by the authors across eight years, this study proposes the ‘Twin Polynomial Method’ (TPM) to estimate the tri-axial left and right foot GRF(t) signals from the total GRF(t) signals. For each gait cycle, TPM fits polynomials of degree five, eight, and nine to the known single-support part of the left and right foot vertical, anterior-posterior, and medial-lateral GRF(t) signals, respectively, to extrapolate the unknown double-support parts of the corresponding GRF(t) signals. Validation of the proposed method both with force plate measurements (gold standard) in the laboratory, and in real-life environment showed a peak-to-peak normalized root mean square error of less than 2.5%, 6.5% and 7.5% for the estimated GRF(t) signals in the vertical, anterior-posterior and medial-lateral directions, respectively. These values show considerable improvement compared with the currently available GRF(t) decomposition methods in the literature.The authors acknowledge the financial support provided by the UK Engineering and Physical Sciences Research Council (EPSRC) for the following research grants: Frontier Engineering Grant EP/K03877X/1 (Modelling complex and partially identified engineering problems: Application to the individualized multiscale simulation of the musculoskeletal system); and Platform Grant EP/G061130/2 (Dynamic performance of large civil engineering structures: an integrated approach to management, design and assessment)

Quantification of dynamic excitation potential of pedestrian population crossing footbridges

This is the final version. Available on open access from Hindawi via the DOI in this recordDue 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. © 2011 - IOS Press and the authors. All rights reserved.Engineering and Physical Sciences Research Council (EPSRC

Making sense of bridge monitoring: Vision for the future

PublishedThis paper presents a vision for the future monitoring systems which will become normal requirements for management of bridges as key objects of national infrastructure in the UK and elsewhere. Rather than being pushed by authorities and legislation, we expect that bridge managers will recognize the clear business cases for investing in well-designed targeted monitoring. To support this proposition, the paper presents two case studied where state-of-the-art bridge monitoring technology was used or potentially could be used to: • Decide when to inspect and change bridge bearings, and • Decide when to close various traffic lanes to reduce probability of overstressing bridge structural components. © 2013 Taylor & Francis Group

Duality between time and frequency domains for vibration serviceability analysis of floor structures

This is the final version of the article. Available from Elsevier via the DOI in this record.For vibration serviceability of floors, current design guidelines adopt different criteria to assess vibration levels due to human walking dynamic excitation. Whatever the adopted criterion is, it requires a quantified vibration response of the structure. This quantification could be achieved following either a time- or a frequency-domain approach to response analysis. Each approach has its advantages and disadvantages. For instance, when using the time-domain analysis, exact time-domain amplitudes of the response time histories could be quantified but the process could take time. On the other hand, a frequency-domain analysis approach could reduce the calculation time, but it is impossible to recover exact time-domain amplitudes of the response, which is essentially averaged by the process of calculation. In this paper, the theoretical duality between time and frequency domains is examined practically in the context of vibration serviceability of a floor structure. Weight-normalised vertical ground reaction force (GRF) measured on an instrumented treadmill due to walking is used for that purpose because it has realistic distribution of energy in the frequency domain. This GRF is applied on a finite element model of a reinforced concrete high-frequency floor and the responses are calculated via both time and frequency domain analyses. Comparison of these two methods reveals that time-domain analysis could introduce significant errors in the calculated vibration responses. This is due to the errors in the numerical solution of equation of motion.The paper was prepared with the support of the Engineering and Physical Sciences Research Council (EPSRC) grant reference EP/G061130/1 (Dynamic Performance of Large Civil Engineering Structures: An Integrated Approach to Management, Design and Assessment) for which the writers are grateful. The measured walking force was created courtesy of funding by the UK Engineering and Physical Sciences Research Council, Grant EP/E018734/1 (Human walking and running forces: novel experimental characterization and application in civil engineering dynamics). The financial support of The Higher Committee for Education Development in Iraq (HCED IRAQ scholarship reference GD-13-5) is highly appreciated as well

Human-Structure Dynamic Interaction during Short-Distance Free Falls

The dynamic interactions of falling human bodies with civil structures, regardless of their potentially critical effects, have sparsely been researched in contact biomechanics. The physical contact models suggested in the existing literature, particularly for short-distant falls in home settings, assume the human body falls on a “rigid” (not vibrating) ground. A similar assumption is usually made during laboratory-based fall tests, including force platforms. Based on observations from a set of pediatric head-first free fall tests, the present paper shows that the dynamics of the grounded force plate are not always negligible when doing fall test in a laboratory setting. By using a similar analogy for lightweight floor structures, it is shown that ignoring the dynamics of floors in the contact model can result in an up to 35% overestimation of the peak force experienced by a falling human. A nonlinear contact model is suggested, featuring an agent-based modelling approach, where the dynamics of the falling human and the impact object (force plate or a floor structure here) are each modelled using a single-degree-of-freedom model to simulate their dynamic interactions. The findings of this research can have wide applications in areas such as impact biomechanics and sports science