Single Person Walking Research Articles

Research on Microseismic Source Location Method Based on Waveform Characteristics Monitored by Nanomaterial Sensor under the Background of Metal Oxide Polluted Environment.

In recent years, the monitoring range of source location technology has developed from being one-dimensional and two-dimensional to being three-dimensional. However, due to the complexity and nonuniformity of the seismic wave propagation medium and the uncertainty of the propagation law, there will be large errors in the source location results. Therefore, the analysis of vibration signal has become the key problem of current research. This paper designs a microseismic monitoring system based on Internet of Things sensors, which can monitor the vibration wave characteristics of vibration signals. In order to test the positioning accuracy of the system, this paper introduces three positioning methods: target positioning method based on time difference, time delay estimation method based on EMD, and source target positioning method based on the characteristic frequency of vibration signal. The purpose of this paper is to find the most accurate method from the three source location methods. Through these three methods, the vibration source generated by a single person walking in situ can be located in the vibration positioning experiment of human walking. The error between the actual position and the measurement source position is compared. The results show that the time delay estimation method based on empirical mode decomposition has the highest positioning accuracy. In addition, in the microseismic experiment, it is proved that the positioning accuracy of EMD using L1 norm statistical criterion is higher than that using L2 norm statistical criterion.

Vibration behavior of timber-concrete composite floors under human-induced excitation

The design of timber-concrete composite (TCC) floors is usually subject to the requirement of serviceability rather than strength. Most studies reported so far focus on the dynamic characteristics of the TCC floor. However, there are few studies conducted on the vibration comfort of TCC floors under human-induced excitation. In this paper, dynamic experiments were performed to obtain the fundamental frequency and the damping ratio of a glulam-concrete composite floor under simply supported and fixed support boundary conditions, respectively. Besides, an in-depth investigation was carried out considering the influences of walking path, step frequency, number of pedestrians, arrangement of walking loads and walking mode on the vibration response of the composite floor. Test results showed that the peak acceleration of the floor increased with an increase in step frequency and the number of pedestrians. Regular walking caused a higher peak acceleration compared to irregular walking. At the same step frequency, marking time caused a larger peak acceleration than normal walking. Three existing analytical models were applied to predict the fundamental frequency of the floor, which conformed to the experimental results. In addition, a calculation model and finite element (FE) models were proposed to predict the peak floor acceleration under a single person walking, and the numerical model results agree well with the test results. A double-index was proposed to evaluate the vibration serviceability of TCC floors; the fundamental frequency of the floor is required to exceed 15 Hz and the peak acceleration ought to be less than 0.15 m/s2.

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

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.

Multi-Gait Recognition Based on Attribute Discovery

Gait recognition is an important topic in biometrics. Current works primarily focus on recognizing a single person's walking gait. However, a person's gait will change when they walk with other people. How to recognize the gait of multiple people walking is still a challenging problem. This paper proposes an attribute discovery model in a max-margin framework to recognize a person based on gait while walking with multiple people. First, human graphlets are integrated into a tracking-by-detection method to obtain a person's complete silhouette. Then, stable and discriminative attributes are developed using a latent conditional random field (L-CRF) model. The model is trained in the latent structural support vector machine (SVM) framework, in which a new constraint is added to improve the multi-gait recognition performance. In the recognition process, the attribute set of each person is detected by inferring on the trained L-CRF model. Finally, attributes based on dense trajectories are extracted as the final gait features to complete the recognition. The experimental results demonstrate that the proposed method achieves better recognition performance than traditional gait recognition methods under the condition of multiple people walking together.

Walking load model for single footfall trace in three dimensions based on gait experiment

This paper investigates the load model for single footfall trace of human walking. A large amount of single person walking load tests were conducted using the three-dimensional gait analysis system. Based on the experimental data, Fourier series functions were adopted to model single footfall trace in three directions, i.e. along walking direction, direction perpendicular to the walking path and vertical direction. Function parameters such as trace duration time, number of Fourier series orders, dynamic load factors (DLFs) and phase angles were determined from the experimental records. Stochastic models were then suggested by treating walking rates, duration time and DLFs as independent random variables, whose probability density functions were obtained from experimental data. Simulation procedures using the stochastic models are presented with examples. The simulated single footfall traces are similar to the experimental records.

Vibration Performance Assessment of a Long-Span Concrete Floor Using Field Measurements over a Five-Year Period

Field tests were conducted on a unique long-span post-tensioned concrete floor between 2008 and 2013. The measurements cover the important construction stages including completion of the structural floor, installation of the false floor, completion of the whole building and opening the building to the public. This paper assesses the vibration performance of the floor using field measurements. Natural frequencies, damping ratios, mode shapes and modal masses of the floor were identified from ambient vibration measurements for eight different stages. A clear decreasing trend of the natural frequencies has been observed since 2009 when the building was opened to the public. Moreover, the natural frequencies decrease while the damping ratio increases with increasing vibration amplitude. It is found that, in this case, the false floor provides no contribution to the stiffness or the damping of the structural floor. Peak responses of the floor under controlled excitation, such as a single person walking and a group of people walking, are compared. Peak responses of the floor under operational excitation are presented, including the annual maximum response for four continuous years and the maximum responses for different numbers of occupants.

Acceleration response spectrum for predicting floor vibration due to occupant walking

Abstract Annoying vibrations caused by occupant walking is an important serviceability problem for long-span floors. At the design stage the floor׳s structural arrangement may frequently change to cater for the owner׳s varying requirements. An efficient and accurate approach for predicting a floor׳s acceleration response is thus of great significance. This paper presents a design-oriented acceleration response spectrum for calculating a floor׳s response given the floor׳s modal characteristics and a specified confidence level. 2204 measured footfall traces from 61 test subjects were used to generate 10 s peak root-mean-square acceleration response spectra, on which a piecewise mathematical representation is based. The proposed response spectrum consists of three main parts: the first harmonic plateau ranging from 1.5 to 2.5 Hz, the second harmonic plateau ranging from 3.0 to 5.0 Hz and the descending part going with frequencies from 5.0 to 10.0 Hz. The representative value of each plateau and the mathematical representation for the descending curve were determined statistically for different confidence levels. Furthermore, the effects of factors, such as floor span, occupant stride length, higher modes of vibration, boundary conditions and peak acceleration response, on the proposed spectrum have been investigated and a modification measure for each factor is suggested. A detailed application procedure for the proposed spectrum approach is presented and has been applied to four existing floors to predict their acceleration responses. Comparison between predicted and field measured responses shows that the measured accelerations of the four floors are generally close to or slightly higher than the predicted values for the 75 percent confidence level, but are all lower than the predicted values for the 95 percent confidence level. Therefore the suggested spectrum-based approach can be used for predicting a floor׳s response subject to a single person walking.

Field measurements and assessment of vibration serviceability of as-built long-span concrete floor

Vertical vibration serviceability of an as-built concrete floor, whose 41.55 m span is currently the longest in China, are investigated in this paper by field measurements and numerical analysis. A vibration monitoring system were designed and installed on the floor. Different types of human-induced excitation are simulated such as single person walking, multi-person walking at the same pace rate, multi-person jumping and multi-person randomly walking. The dynamic properties and responses of the floor are also computed using finite element method. It is found in this paper that the acceleration vibration amplitudes of the floor under different excitations are lower than the limitation. The amplitudes of floor response are quite different for different types of excitation. The response of wooden floor is much higher than the structure floor at the same location therefore, cannot be directly adopted for serviceability assessment. The fundamental frequency of the floor can be accurately predicted if the mass properties and boundary conditions are properly modelled. Finally, it is suggested that the vibration amplitude control is much more important than frequency control for vibration serviceability design of long-span concrete floor.

Methods for person identification on a pressure-sensitive floor: Experiments with multiple classifiers and reject option

This paper presents methods for footstep-based person identification using a large pressure-sensitive floor with a sensory system. The aim was to analyse and compare different pattern classification methods for their ability to solve this particular problem as well as to introduce some novel and useful methodological extensions, which can improve classification accuracy and the adaptability of the system. These extensions are based on the conditional posterior probability outputs of classifiers, i.e., efforts to combine classifiers trained with different feature sets and to combine multiple footstep instances of a single person walking on the floor. Additionally, a method to reject unreliable examples in order to increase accuracy was applied to the system. The experiments demonstrated the usefulness of these methods. An identification method that uses a combination of multiple classifiers and multiple examples yielded very promising results with an overall accuracy rate of 92% for ten different walkers. When the reject option was added, a classification rate of 95% with a 9% rejection rate was achieved. This methodology can be applied to smart room applications where a small number of persons need to be identified.

Probability-based prediction of multi-mode vibration response to walking excitation

In vibration serviceability checks of footbridges, a force induced by a single person walking is usually modelled as a harmonic force having a frequency that matches one of the footbridge natural frequencies. This approach assumes that, among the infinite number of harmonics a walking force is composed of, only a single harmonic is important for a vibration serviceability check. Another usual assumption is that the footbridge can be modelled as an SDOF system, implying that only vibration in a single mode is of interest. In addition, due to the deterministic nature of this approach, it cannot take into account inter- and intra-subject variabilities in the walking force that are now well documented in the literature. To account for these variabilities, a novel probabilistic approach to carry out a vibration serviceability check is developed in this paper. Factors such as the probability distribution of walking frequencies, step lengths and amplitude of walking force for its five lowest harmonics and subharmonics are taken into account. Using walking force time histories measured on a treadmill, the frequency content of the force was investigated, resulting in the formulation of a multi-harmonic force model. This model can be used to estimate the multi-mode response in footbridges. This was verified successfully on an as-built catenary footbridge structure. Although only the vibration response of footbridges was analysed in this paper, the force model proposed has the potential to be implemented in the estimation of floor vibration as well, where multi-mode response occurs more frequently. The model is easily programmable and as such could present a powerful tool for estimating efficiently the probability of various levels of vibration response due to single person walking. Therefore, the proposed probability-based methodology has the potential to revolutionise the philosophy of the current codes of practice dealing with vibration serviceability of structures under human-induced vibration.

Human–structure dynamic interaction in footbridges

Dynamic load induced in the vertical direction by a single person walking across a footbridge structure is usually modelled as a resonant harmonic force. A comparison between modal responses generated by this harmonic force and a walking force measured on a treadmill confirmed that using the harmonic force is justifiable in the case of walking across a structure that does not vibrate perceptibly. It is further shown that using this harmonic force for predicting the response of a perceptibly vibrating footbridge can significantly overestimate the real footbridge response and therefore its degree of liveliness. This is because of the inability of pedestrians to keep pacing steadily when perceiving strong vibrations. A methodology for systematic comparison of the measured and simulated responses is proposed with the aim of identifying vibration levels which disturb normal walking. On two footbridges investigated this level was 0·33 m/s2 and 0·37 m/s2, in both cases being lower than the levels allowed by the current British footbridge design code. Finally, the observed effect of losing steady walking step can be expressed via either increased damping or modified harmonic dynamic force over time periods when test subjects lose their step. The average increase in the damping over the analysed time periods of imperfect walking was up to 10 times higher than the damping of an empty footbridge.

EVALUATION OF MATHEMATICAL MODELS FOR PREDICTING WALKING-INDUCED VIBRATIONS OF HIGH-FREQUENCY FLOORS

This paper evaluates performance of three representative single-person walking excitation models which can be used to check vibration levels of high-frequency building floors accommodating highly sensitive equipment. The three models calculate vibration responses by harmonic, transient and spectral analyses, respectively. The evaluation was based on a combined experimental and analytical work comprising modal testing of a prototype floor, repeated measurements of walking-induced vibrations, finite element modelling and model updating to match the measured modal properties. The updated and verified model was then used for the application of the three walking models results of which were then compared with their experimental counterparts. It was found that all three models were on the "safe" side and overestimated responses measured in all response tests. However, the harmonic model which assumes high-frequency floor resonance caused by the 7th or 8th harmonic of the walking resulted in over-conservative response estimates order of magnitude higher than the maximum measured values in all response tests. Nevertheless, the model which describes walking across a high-frequency floor as pulses representing footfalls consistently overestimated responses by just about 20% and is, therefore, recommended for vibration serviceability checks of this type of floors.