The experiments involving walking individuals are performed in cooperation with Movement &#38; posture Analysis Laboratory Leuven (MALL)25. Their cooperation and support is gratefully acknowledged.

All procedures were approved by the ethical committee of the university hospital of the KU Leuven and each subject gave a written informed consent prior to participation.
1. 3D Motion Tracking: Configuration and Data Acquisition
<ol>
	<li>Ensure that the individual sensors are fully charged (Figure 1A). This step takes about 1 hr but can be performed on the days prior to the actual measurements. Follow the manufacturer&#39;s charging protocol.</li>
	<li>MT Manager &#8212; Data acquisition2:
	<ol>
		<li>Enable the wireless connection with the sensors and specify the desired sample rate (Wireless Configuration &#62; Enable all wireless masters). 
		Note: To allow for an accurate characterization of the pedestrian behavior, a sampling rate of at least 60 Hz is advised. The individual sensors record 3D linear acceleration, angular velocity (earth) magnetic field and atmospheric pressure data.</li>
		<li>Activate the operational mode and initiate the measurement mode: make slow movements with the sensors for about 1 min (Wireless Configuration &#62; Start measurement on all wireless masters).</li>
		<li>Display inertial and magnetic data of all active sensors (View &#62; Display &#62; Inertial Data). Make sure that, while stationary, the orientation of the sensor does not chance. 
		Note: A changing orientation of the stationary sensor would indicate a magnetically disturbed environment and, thereby, inaccurate orientation information.</li>
	</ol>
	</li>
	<li>Orientation reset: Apply an object/heading reset (Object/heading reset &#62; Reset orientation) to define the global reference frame of the experiments (Figure 1B) 2.</li>
	<li>Place the sensor as close as possible to the body center of mass (CoM) located at the level of the fifth lumbar vertebrae (Figure 1C). Fasten a single sensor tightly and robustly onto each participant with specially designed click-in full body straps (Figure 1C).</li>
	<li>Record data as required.</li>
	<li>Load the records of interest (open file), specify the export settings (Tools &#62; Preferences &#62; Exporters) and export the acceleration (and orientation matrix) data for subsequent analysis2 (File &#62; Export).</li>
</ol>
2. Force Plate: Setup and Configuration
Note: The present step discusses the application of a force plate to register the GRFs. In the case that a walking/running person is involved, a series of force plates or an instrumented treadmill is to be used to register the loading induced by subsequent steps3, the protocol itself is analogous.
<ol>
	<li>Ensure that the force plate is securely fixed to the laboratory floor (Figure 2).</li>
	<li>Configure the device and acquisition settings4 (NDI Open Capture &#62; Data &#62; Device Settings &#62; Settings). Select the proper &#34;gain&#34; and &#34;sample rate&#34;. Configure and check the external trigger settings, if required4.
	<ol>
		<li>Choose the gain and sample rate in accordance with the desired accuracy and the involved loading type. For the present application, use a gain of 128 (Maximum Force 4,879 N) and a sample rate 200 Hz.</li>
	</ol>
	</li>
	<li>Start and end each trial with an empty force plate: Tare the force plate when empty (NDI Open Capture &#62; Data &#62; Device Settings &#62; Settings &#62; Tare).</li>
	<li>For verification purposes: Place a known weight on top of the force plate before and after each trial. 
	Note: In the present application a mass of 5 kg is used, however, the use of another well-known rigid mass (&#62; 2 kg) can equally serve this verification test.</li>
	<li>Record and save the GRF data as required. Export the GRFs for subsequent analysis4.</li>
</ol>
3. Measurement of the Structural Accelerations
Note: The present steps aim to collect the structural vibrations at one or more relevant locations on the structure. The present application employs GeoSIG GMS recorders (Figure 3) to register the structural accelerations. Other sensor types with proper characteristics for the involved application, can be equally applied.
<ol>
	<li>Ensure that the individual sensors are fully charged. This step can take several hours but can be performed on the days prior to the actual measurements. Follow the manufacturer&#39;s charging protocol.</li>
	<li>Install the sensors on the desired locations of the primary structure: level the sensors and, if necessary, provide proper fixation to the primary structure (e.g., by using magnets). 
	Note: given the high mass of the individual GMS recorders (&#62; 6 kg) and the involved low-frequency oscillations (&#60; 6 Hz), no additional fixation was necessary in this case.</li>
	<li>For GeoDAS Data acquisition5: Configure and enable the wireless GMS network and connection with the sensors5. Check time settings and synchronization settings (if necessary) (right click on the sensor &#62; More information).</li>
	<li>Position the sensors on the desired location and level them in agreement with the global reference frame.</li>
	<li>For GeoDAS Data acquisition5: Export the recorded data for subsequent analysis (right click on the sensor &#62; Instrument Control &#62; Send a request &#62; User request &#62; GETEVT5).</li>
</ol>
4. Experiments in a Controlled Laboratory Environment
<ol>
	<li>Configure / Setup 3D motion tracking (as discussed in section 1).</li>
	<li>Configure / Setup force plate (as discussed in section 2).</li>
	<li>During operation: visually check the real-time measurements of both the wireless inertial sensors and the force plate to verify their operational mode.</li>
	<li>Ask the participant to step onto the force plate and stand still for at least 30 sec: this allows to identify the weight of each individual.</li>
	<li>Configure the metronome signal: select the desired rhythm, i.e., fundamental forcing frequency. 
	Note: The metronome signal can be easily configured using free online or smartphone applications.</li>
	<li>Start recording the data of both the force plate and the wireless inertial sensors.</li>
	<li>Ask the participant to initiate the desired activity: walking, jumping or bobbing at the (targeted pacing) rate as indicated by the metronome signal (see Figure 4).</li>
	<li>Record the chosen number of loading cycles, e.g., steps, jumps or bobbing cycles. Ask the participant to get off the force plate. 
	Note: For validation purposes it is advised to consider some additional recording time in these unloaded conditions. In literature, there is no clear consensus about the minimum number loading cycles required to characterize the cycle-to-cycle variabilities6. Based on experience and the work presented in [6], the study presented here considers 60 consecutive cycles whereby the first and last five loading cycles are excluded from the further analysis to exclude irregularities in the loading pattern at the start and end of the trial.</li>
</ol>
5. Experiments In Situ
<ol>
	<li>Configure / Setup the network of 3D inertial sensors that track the motion of the participants (see section 2 and Figure 5).</li>
	<li>Configure / Setup the GMS network of wireless accelerometers that register the structural accelerations (see section 4).</li>
	<li>During operation: (visually) check the real-time measurements of the wireless inertial sensors to verify their operational mode.</li>
	<li>Define a clear protocol that allows to synchronize the involved measurement systems, if required. 
	Note: This step is necessary when the involved data acquisition systems do not allow for direct synchronization due to the lack of a trigger or common channel. The latter is the case for the wireless measurement systems applied in the in situ experiments (5.1 and 5.2). Therefore, a clear protocol has been adopted on site that allows to synchronize the datasets offline. In the present application, the involved measurement systems are synchronized through registration of an identical event, i.e., impact, at the beginning and end of each trial, registered by at least one sensor of each of the involved measurement systems. Properly aligned time vectors are subsequently obtained through offline alignment of these events.</li>
	<li>Configure the metronome signal: in situ, the use of a megaphone to amplify the targeted beat is required.</li>
	<li>Collect a sufficient number of trials to check the repeatability of the experiment. Based on experience, the authors recommend to record at least 3, or preferably 4, trials.</li>
</ol>
6. Data Analysis
<ol>
	<li>Pre-process the raw data of the involved equipment as required: Apply the proper filters to remove undesired influences such as irrelevant high-frequency contributions and measurement noise, and retain the relevant time window according to manufacturer&#39;s protocol. 
	Note: The filtering characteristics should be chosen in accordance with the application. In the present study, the MATLAB Signal Processing Toolbox7 is applied to perform a low-pass filtering with a cut-off frequency at 20 Hz for all involved signals.</li>
	<li>For each participant: Compute the discrete Fourier transform of the registered accelerations of the CoM using MATLAB Signal Processing Toolbox7 and identify the average loading frequency as the frequency of the dominant peak of the fundamental harmonic in the obtained spectrum.</li>
	<li>Identify the time in between any two nominally identical events of the load cycles using the method detailed in [3] or the lc_timing tool of the PediVib MATLAB toolbox8
	<ol>
		<li>Load the data vector (lc_timing &#62; Load).</li>
		<li>Specify the sampling rate and estimate the average loading frequency. Specify the relevant time window, if required. Save the identified timing of the nominally identical events, i.e., load cycles (lc_timing &#62; Save).</li>
	</ol>
	</li>
	<li>Compute the average loading frequency as the inverse of the average time in between the subsequent load cycles (as identified in 6.3).</li>
	<li>For the experiments in the laboratory: Apply the procedure detailed in 6.3 for both the resulting ground reaction forces and the accelerations registered at the CoM of each individual. 
	Note: This step serves as validation for the procedure as applied for the in situ experiments where the GRFs cannot be measured directly. The method detailed in [3] shows how the time variant pacing rate of the pedestrian can be identified by characterizing the relation between the accelerations registered near the CoM of the individual and the consequent GRFs.</li>
	<li>For the experiments in situ: Apply the procedure detailed in 6.3 for the accelerations registered at the CoM of each individual.</li>
</ol>
7. Simulation and Analysis of the Structural Response
Note: The subsequent steps are performed using MATLAB7. The structural response is computed using the PediVib toolbox, a MATLAB toolbox developed by the authors8 (Figure 6): the human-induced forces are determined through application of the generalized load models of defined by Li et al.9 (walking) and Bachmann et al.1 (jumping, running and vandal loading), and the structural model is formulated in modal coordinates10. The accompanying manual includes tutorials that clearly illustrate the following steps.
<ol>
	<li>Simulation of the structural response
	<ol>
		<li>Define the modal parameters of the test structure: Natural frequencies, modal damping ratios, mass-normalized modal displacements, coordinates of the corresponding nodes (PediVib &#62; Structural parameters &#62; New). Visually check the modal input information (PediVib &#62; Structural parameters &#62; View).</li>
		<li>Define the characteristics of the pedestrian and the corresponding induced loads: load type, weight, walking path/location, average pacing rate, onset of each load cycle (PediVib &#62; Single pedestrian &#62; New). Run and save the simulated structural response for the involved participants. Visually check the results (PediVib &#62; Single pedestrian &#62; View).</li>
	</ol>
	</li>
	<li>Compute the total structural response through superposition of the individual responses, i.e., summation of the corresponding vectors, and compare the result with the measured structural response, e.g., by creating a figure which displays the measured and simulated structural response.</li>
</ol>

<ol>
	<li>Bachmann, H., Ammann, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Bachmann vibrations in structures : induced by man and machines. , (1987).</li><li>. MTw User Manual Available from: <a target="_blank" href="https://www.xsens.com/download/usermanual/MTw_usermanual.pdf">https://www.xsens.com/download/usermanual/MTw_usermanual.pdf</a> (2013)</li><li>Van Nimmen, K., Lombaert, G., Jonkers, I., De Roeck, G., Vanden Broeck, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterisation+of+walking+loads+by+3D+inertial+motion+tracking.">Characterisation of walking loads by 3D inertial motion tracking.</a> J. Sound Vib. 333 (20), 1-15 (2013).</li><li>Northern Digital Inc. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> TrueImpulse Kinetic Measurement System User Guide. , (2013).</li><li>Racic, V., Pavic, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mathematical+model+to+generate+near-periodic+human+jumping+force+signals.">Mathematical model to generate near-periodic human jumping force signals.</a> Mech. Syst. Signal Process. 24 (1), 138-152 (2010).</li><li>The MathWorks Inc. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> MATLAB and Signal Processing Toolbox Release. , (2014).</li><li>Van Nimmen, K., Van den Broeck, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> PediVib 1.0 - A MATLAB toolbox for the simulation of human-induced vibrations. , (2015).</li><li>Li, Q., Fan, J., Nie, J., Li, Q., Chen, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Crowd-induced+random+vibration+of+footbridge+and+vibration+control+using+multiple+tuned+mass+dampers.">Crowd-induced random vibration of footbridge and vibration control using multiple tuned mass dampers.</a> J. Sound Vib. 329 (19), 4068-4092 (2010).</li><li>Van Nimmen, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Numerical and experimental study of human-induced vibrations of footbridges [dissertation]. , (2015).</li><li>Middleton, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Dynamic performance of high frequency floors [dissertation]. , (2009).</li><li>Ing&#242;lfsson, E. T., Georgakis, C. T., Ricciardelli, F., J&#246;nsson, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Experimental+identification+of+pedestrian-induced+lateral+forces+on+footbridges.">Experimental identification of pedestrian-induced lateral forces on footbridges.</a> J. Sound Vib. 330 (6), 1265-1284 (2011).</li><li>Racic, V., Brownjohn, J. M. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mathematical+modelling+of+random+narrow+band+lateral+excitation+of+footbridges+due+to+pedestrians+walking.">Mathematical modelling of random narrow band lateral excitation of footbridges due to pedestrians walking.</a> Comput. Struct. 90-91 (1), 116-130 (2012).</li><li>Reynders, E., Roeck, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=De+Reference-based+combined+deterministic-stochastic+subspace+identification+for+experimental+and+operational+modal+analysis.">De Reference-based combined deterministic-stochastic subspace identification for experimental and operational modal analysis.</a> Mech. Syst. Signal Process. 22 (3), 617-637 (2008).</li><li>Bocian, M., Macdonald, J. H. G., Burn, J. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biomechanically+inspired+modeling+of+pedestrian-induced+vertical+self-excited+forces.">Biomechanically inspired modeling of pedestrian-induced vertical self-excited forces.</a> J. Bridg. Eng. 18 (12), 1336-1346 (2013).</li><li>&#381;ivanovi&#263;, S., Pavi&#263;, A., Ing&#242;lfsson, E. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Modeling+spatially+unrestricted+pedestrian+traffic+on+footbridges.">Modeling spatially unrestricted pedestrian traffic on footbridges.</a> Journal of Structural Engineering. 136 (10), 1296-1308 (2010).</li><li>Agu, E., Kasperski, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Influence+of+the+random+dynamic+parameters+of+the+human+body+on+the+dynamic+characteristics+of+the+coupled+system+of+structurecrowd.">Influence of the random dynamic parameters of the human body on the dynamic characteristics of the coupled system of structurecrowd.</a> J. Sound Vib. 330 (3), 431-444 (2011).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Vicon Motion Systems Product Manuals. , (2012).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> CODAmotion Technical data sheet. , (2012).</li><li>Meichtry, A., Romkes, J., Gobelet, C., Brunner, R., M&#252;ller, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Criterion+validity+of+3D+trunk+accelerations+to+assess+external+work+and+power+in+able-bodied+gait.">Criterion validity of 3D trunk accelerations to assess external work and power in able-bodied gait.</a> Gait Posture. 25 (1), 25-32 (2007).</li><li>Jung, Y., Jung, M., Lee, K., Koo, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ground+reaction+force+estimation+using+an+insole-type+pressure+mat+and+joint+kinematics+during+walking.">Ground reaction force estimation using an insole-type pressure mat and joint kinematics during walking.</a> J. Biomech. 47 (11), 2693-2699 (2014).</li><li>Liedtke, C., Fokkenrood, S. A., Menger, J. T., van der Kooij, H., Veltink, P. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evaluation+of+instrumented+shoes+for+ambulatory+assessment+of+ground+reaction+forces.">Evaluation of instrumented shoes for ambulatory assessment of ground reaction forces.</a> Gait Posture. 26 (1), 39-47 (2007).</li><li>Boutaayamou, M., Schwartz, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Validated+extraction+of+gait+events+from+3D+accelerometer+recordings.">Validated extraction of gait events from 3D accelerometer recordings.</a> , 6-9 (2012).</li><li>Kavanagh, J. J., Menz, H. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Accelerometry:+A+technique+for+quantifying+movement+patterns+during+walking.">Accelerometry: A technique for quantifying movement patterns during walking.</a> Gait Posture. 28 (1), 1-15 (2008).</li><li>. MALL: Movement and posture Analysis Laboratory Leuven (Interdepartemental research laboratory at the Faculty of Kinisiology and Rehabilitation Sciences) Available from: <a target="_blank" href="https://faber.kuleuven.be/MALL/mall.php">https://faber.kuleuven.be/MALL/mall.php</a> (2015)</li></ol>

The authors have nothing to disclose.

The human motion and resulting GRFs are usually identified by the application of force plates, instrumented treadmills as well as optical motion capture technology such as Vicon18 and CODA19. The application of these techniques is, however, restricted to the laboratory environment. In answer to this drawback, the potential of innovative techniques that permit the measurement of &#39;natural&#39; person behavior over many repeated and uninterrupted cycles is currently investigated20. Alter...

Driven by the economic demand of efficiency and the increasing strength of (new) materials, architects and engineers are pushing the limits to build ever longer, taller and lighter structures. Typically, light and slender structures have one or more natural frequencies that lie within the dominant spectrum of common human activities such as walking, running or jumping. Likely to be subject to (near-)resonant excitation, they are often unduly responsive to human motion, resulting in disturbing or even harmful vibrations1. For these slender and lightweight structures, the vibration serviceability is a matter of growing concern, often constituting the critical design requirement.
The human motion and the resulting ground reaction forces (GRFs) are usually experimentally identified in laboratory conditions. Currently, designers are forced to rely on &#8212; what are assumed to be &#39;conservative&#39;&#160;&#8212; equivalent load models, upscaled from single-person force measurements. With designs governed by the dynamic performance under high crowd densities, a strong demand exists for the verification and refinement of the currently available load models.
The present protocol employs a 3D inertial motion tracking technique for the characterization of the natural motion of pedestrians. It is shown how this information can be used to define the correlation among the pedestrians as well as the corresponding induced loads. In a subsequent step, the characterized pedestrian behavior is used to numerically simulate the induced structural response. Comparison with the registered structural response allows to quantify the effect of unaccounted human-structure interaction phenomena, e.g., the added damping due to the presence of the pedestrians. The methodology is illustrated for full-scale experiments on a real footbridge where the structural response and the motion of the participants are registered simultaneously.

<table border="0" cellpadding="0" cellspacing="0" width="1081">
	<tbody>
		<tr height="65">
			<td height="65" style="height:65px;width:301px;">MTw Development Kit + MT Manager Software</td>
			<td style="width:107px;">Xsens</td>
			<td style="width:280px;">MTW-38A70G20-1</td>
			<td style="width:393px;">Development kit with wireless, highly accurate, small and lightweight 3D human motion trackers and accompanying click-in full body straps.</td>
		</tr>
		<tr height="65">
			<td height="65" style="height:65px;width:301px;">True Impulse Kinetic Measurement System + NDI Open Capture Data Acquisition and Visualization System</td>
			<td style="width:107px;">NDI Northern Digital Inc.</td>
			<td style="width:280px;">791028</td>
			<td style="width:393px;">TrueImpulse measures reaction forces exerted by humans during a wide variety of activities.</td>
		</tr>
		<tr height="65">
			<td height="65" style="height:65px;width:301px;">GMS-24</td>
			<td style="width:107px;">GeoSIG Ltd</td>
			<td style="width:280px;">Rev. 03.08.2010</td>
			<td style="width:393px;">(Wireless) accelerometers to register the structural vibrations.</td>
		</tr>
		<tr height="65">
			<td height="65" style="height:65px;width:301px;">GeoDAS GeoSIG Data Acquisition System</td>
			<td style="width:107px;">GeoSIG Ltd</td>
			<td style="width:280px;">Rev. 03.08.2010</td>
			<td style="width:393px;">Graphical MS Windows application running under Windows 9x/NT/2000, providing a software interface between users and GeoSIG recorders GSR/GCR/GBV/GT.</td>
		</tr>
		<tr height="65">
			<td height="65" style="height:65px;width:301px;">PediVib toolbox</td>
			<td style="width:107px;">KU Leuven</td>
			<td style="width:280px;">/</td>
			<td style="width:393px;">Software interface/toolbox to simulate the structural vibrations induced by pedestrians.</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:301px;">Metronome</td>
			<td style="width:107px;">/</td>
			<td style="width:280px;">/</td>
			<td style="width:393px;">A device to indicate the targetted pacing rate of the activity (free applications are available online for pc/laptop/smartphone).</td>
		</tr>
	</tbody>
</table>

simulation of human-induced vibrations based on the characterized in-field pedestrian behavior

For slender and lightweight structures, vibration serviceability is a matter of growing concern, often constituting the critical design requirement. With designs governed by the dynamic performance under human-induced loads, a strong demand exists for the verification and refinement of currently available load models. The present contribution uses a 3D inertial motion tracking technique for the characterization of the in-field pedestrian behavior. The technique is first tested in laboratory experiments with simultaneous registration of the corresponding ground reaction forces. The experiments include walking persons as well as rhythmical human activities such as jumping and bobbing. It is shown that the registered motion allows for the identification of the time variant pacing rate of the activity. Together with the weight of the person and the application of generalized force models available in literature, the identified time-variant pacing rate allows to characterize the human-induced loads. In addition, time synchronization among the wireless motion trackers allows identifying the synchronization rate among the participants. Subsequently, the technique is used on a real footbridge where both the motion of the persons and the induced structural vibrations are registered. It is shown how the characterized in-field pedestrian behavior can be applied to simulate the induced structural response. It is demonstrated that the in situ identified pacing rate and synchronization rate constitute an essential input for the simulation and verification of the human-induced loads. The main potential applications of the proposed methodology are the estimation of human-structure interaction phenomena and the development of suitable models for the correlation among pedestrians in real traffic conditions.

First, it is shown how the accelerations registered near the CoM of the individuals can be used to characterize the consequent GRFs. The results are discussed here for a walking individual3. Fully comparable observations are made when rhythmical human activities, i.e., jumping and bobbing, are considered. Figure 7A and 7B show that the amplitude spectrum of the continuous vertical foot forces and the corresponding acceleration levels r...

Watch this Scientific Journal Video about Simulation of Human-induced Vibrations Based on the Characterized In-field Pedestrian Behavior at JoVE.com

Simulation of Human-induced Vibrations Based on the Characterized In-field Pedestrian Behavior

A protocol is presented for the characterization of the in-field pedestrian behavior and the simulation of the resulting structural response. Field-tests demonstrate that the in situ identified pacing rate and synchronization rate among the participants constitute an essential input for the simulation and verification of the human-induced loads.

For slender and lightweight structures, vibration serviceability is a matter of growing concern, often constituting the critical design requirement. With ...

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8.7K Views.  KU Leuven. A protocol is presented for the characterization of the in-field pedestrian behavior and the simulation of the resulting structural response. Field-tests demonstrate that the in situ identified pacing rate and synchronization rate among the participants constitute an essential input for the simulation and verification of the human-induced loads.

Video: Simulation of Human-induced Vibrations Based on the Characterized In-field Pedestrian Behavior

Simulation, Fabrication and Characterization of THz Metamaterial Absorbers

Metamaterials (MM), artificial materials engineered to have properties that may not be found in nature, have been widely explored since the first theoretical1 and experimental demonstration2 of their unique properties. MMs can provide a highly controllable electromagnetic response, and to date have been demonstrated in every technologically relevant spectral range including the optical3, near IR4, mid IR5 , THz6 , mm-wave7 , microwave8 and radio9 bands. Applications include perfect lenses10, sensors11, telecommunications12, invisibility cloaks13 and filters14,15. We have recently developed single band16, dual band17 and broadband18 THz metamaterial absorber devices capable of greater than 80% absorption at the resonance peak. The concept of a MM absorber is especially important at THz frequencies where it is difficult to find strong frequency selective THz absorbers19. In our MM absorber the THz radiation is absorbed in a thickness of ~ &lambda;/20, overcoming the thickness limitation of traditional quarter wavelength absorbers. MM absorbers naturally lend themselves to THz detection applications, such as thermal sensors, and if integrated with suitable THz sources (e.g. QCLs), could lead to compact, highly sensitive, low cost, real time THz imaging systems.

This protocol outlines the simulation, fabrication and characterization of THz metamaterial absorbers. Such absorbers, when coupled with an appropriate sensor, have applications in THz imaging and spectroscopy.

Metamaterials (MM),  artificial materials engineered to have properties that may not be found in  nature, have been widely explored since the first ...

Simulation of the Planetary Interior Differentiation Processes in the Laboratory

A planetary interior is under high-pressure and high-temperature conditions and it has a layered structure. There are two important processes that led to that layered structure, (1) percolation of liquid metal in a solid silicate matrix by planet differentiation, and (2) inner core crystallization by subsequent planet cooling. We conduct high-pressure and high-temperature experiments to simulate both processes in the laboratory. Formation of percolative planetary core depends on the efficiency of melt percolation, which is controlled by the dihedral (wetting) angle. The percolation simulation includes heating the sample at high pressure to a target temperature at which iron-sulfur alloy is molten while the silicate remains solid, and then determining the true dihedral angle to evaluate the style of liquid migration in a crystalline matrix by 3D visualization. The 3D volume rendering is achieved by slicing the recovered sample with a focused ion beam (FIB) and taking SEM image of each slice with a FIB/SEM crossbeam instrument. The second set of experiments is designed to understand the inner core crystallization and element distribution between the liquid outer core and solid inner core by determining the melting temperature and element partitioning at high pressure. The melting experiments are conducted in the multi-anvil apparatus up to 27 GPa and extended to higher pressure in the diamond-anvil cell with laser-heating. We have developed techniques to recover small heated samples by precision FIB milling and obtain high-resolution images of the laser-heated spot that show melting texture at high pressure. By analyzing the chemical compositions of the coexisting liquid and solid phases, we precisely determine the liquidus curve, providing necessary data to understand the inner core crystallization process.

The high-pressure and high-temperature experiments described here mimic planet interior differentiation processes. The processes are visualized and better understood by high-resolution 3D imaging and quantitative chemical analysis.

A planetary interior is under high-pressure and high-temperature conditions and it has a layered structure. There are two important processes that led to ...

Laboratory Drop Towers for the Experimental Simulation of Dust-aggregate Collisions in the Early Solar System

For the purpose of investigating the evolution of dust aggregates in the early Solar System, we developed two vacuum drop towers in which fragile dust aggregates with sizes up to ~10 cm and porosities up to 70% can be collided. One of the drop towers is primarily used for very low impact speeds down to below 0.01 m/sec and makes use of a double release mechanism. Collisions are recorded in stereo-view by two high-speed cameras, which fall along the glass vacuum tube in the center-of-mass frame of the two dust aggregates. The other free-fall tower makes use of an electromagnetic accelerator that is capable of gently accelerating dust aggregates to up to 5 m/sec. In combination with the release of another dust aggregate to free fall, collision speeds up to ~10 m/sec can be achieved. Here, two fixed high-speed cameras record the collision events. In both drop towers, the dust aggregates are in free fall during the collision so that they are weightless and match the conditions in the early Solar System.

We present a technique to achieve low-velocity to intermediate-velocity collisions between fragile dust aggregates in the laboratory. For this purpose, two vacuum drop-tower setups have been developed that allow collision velocities between &#60;0.01 and ~10 m/sec. The collision events are recorded by high-speed imaging.

For the purpose of investigating the evolution of dust aggregates in the early Solar System, we developed two vacuum drop towers in which fragile dust ...

Selective Area Modification of Silicon Surface Wettability by Pulsed UV Laser Irradiation in Liquid Environment

The wettability of silicon (Si) is one of the important parameters in the technology of surface functionalization of this material and fabrication of biosensing devices. We report on a protocol of using KrF and ArF lasers irradiating Si (001) samples immersed in a liquid environment with low number of pulses and operating at moderately low pulse fluences to induce Si wettability modification. Wafers immersed for up to 4 hr in a 0.01% H2O2/H2O solution did not show measurable change in their initial contact angle (CA) ~75&#176;. However, the 500-pulse KrF and ArF lasers irradiation of such wafers in a microchamber filled with 0.01% H2O2/H2O solution at 250 and 65 mJ/cm2, respectively, has decreased the CA to near 15&#176;, indicating the formation of a superhydrophilic surface. The formation of OH-terminated Si (001), with no measurable change of the wafer&#8217;s surface morphology, has been confirmed by X-ray photoelectron spectroscopy and atomic force microscopy measurements. The selective area irradiated samples were then immersed in a biotin-conjugated fluorescein-stained nanospheres solution for 2 hr, resulting in a successful immobilization of the nanospheres in the non-irradiated area. This illustrates the potential of&#160;the method for selective area biofunctionalization and fabrication of advanced Si-based biosensing architectures. We also describe a similar protocol of irradiation of wafers immersed in methanol (CH3OH) using ArF laser operating at pulse fluence of 65 mJ/cm2 and in situ formation of a strongly hydrophobic surface of Si (001) with the CA of 103&#176;. The XPS results indicate ArF laser induced formation of Si&#8211;(OCH3)x compounds responsible for the observed hydrophobicity. However, no such compounds were found by XPS on the Si surface irradiated by KrF laser in methanol, demonstrating the inability of the KrF laser to photodissociate methanol and create -OCH3 radicals.

We report on a process of in situ alteration of HF treated Si (001) surface into a hydrophilic or hydrophobic state by irradiating samples in microfluidic chambers filled with&#160;H2O2/H2O solution (0.01%-0.5%) or methanol solutions using pulsed UV laser of a relative low pulse fluence.

The wettability of silicon (Si) is one of the important parameters in the technology of surface functionalization of this material and fabrication of ...

Knowledge Based Cloud FE Simulation of Sheet Metal Forming Processes

The use of Finite Element (FE) simulation software to adequately predict the outcome of sheet metal forming processes is crucial to enhancing the efficiency and lowering the development time of such processes, whilst reducing costs involved in trial-and-error prototyping. Recent focus on the substitution of steel components with aluminum alloy alternatives in the automotive and aerospace sectors has increased the need to simulate the forming behavior of such alloys for ever more complex component geometries. However these alloys, and in particular their high strength variants, exhibit limited formability at room temperature, and high temperature manufacturing technologies have been developed to form them. Consequently, advanced constitutive models are required to reflect the associated temperature and strain rate effects. Simulating such behavior is computationally very expensive using conventional FE simulation techniques.
This paper presents a novel Knowledge Based Cloud FE (KBC-FE) simulation technique that combines advanced material and friction models with conventional FE simulations in an efficient manner thus enhancing the capability of commercial simulation software packages. The application of these methods is demonstrated through two example case studies, namely: the prediction of a material's forming limit under hot stamping conditions, and the tool life prediction under multi-cycle loading conditions.

The following paper presents a novel FE simulation technique (KBC-FE), which reduces computational cost by performing simulations on a cloud computing environment, through the application of individual modules. Moreover, it establishes a seamless collaborative network between world leading scientists, enabling the integration of cutting edge knowledge modules into FE simulations.

The use of Finite Element (FE) simulation software to adequately predict the outcome of sheet metal forming processes is crucial to enhancing the ...

Effect of Bending on the Electrical Characteristics of Flexible Organic Single Crystal-based Field-effect Transistors

The charge transport in an organic semiconductor depends highly on the molecular packing in the crystal, which influences the electronic coupling immensely. However, in soft electronics, in which organic semiconductors play a critical role, the devices will be bent or folded repeatedly. The effect of bending on the crystal packing and thus the charge transport is crucial to the performance of the device. In this manuscript, we describe the protocol to bend a single crystal of 5,7,12,16-tetrachloro-6,13-diazapentacene (TCDAP) in the field-effect transistor configuration and to obtain reproducible I-V characteristics upon bending the crystal. The results show that bending a field-effect transistor prepared on a flexible substrate results in nearly reversible yet opposite trends in charge mobility, depending on the bending direction. The mobility increases when the device is bent toward the top gate/dielectric layer (upward, compressive state) and decreases when bent toward the crystal/substrate side (downward, tensile state). The effect of bending curvature was also observed, with greater mobility change resulting from higher bending curvature. It is suggested that the intermolecular &#960;-&#960; distance changes upon bending, thereby influencing the electronic coupling and the subsequent carrier transport ability.

This manuscript describes the bending process of an organic single crystal-based field-effect transistor to maintain a functioning device for electronic property measurement. The results suggest that bending causes changes in the molecular spacing in the crystal and thus in the charge hopping rate, which is important in flexible electronics.

The charge transport in an organic semiconductor depends highly on the molecular packing in the crystal, which influences the electronic coupling ...

Preparation and High-temperature Anti-adhesion Behavior of a Slippery Surface on Stainless Steel

Anti-adhesion surfaces with high-temperature resistance have a wide application potential in electrosurgical instruments, engines, and pipelines. A typical anti-wetting superhydrophobic surface easily fails when exposed to a high-temperature liquid. Recently, Nepenthes-inspired slippery surfaces demonstrated a new way to solve the adhesion problem. A lubricant layer on the slippery surface can act as a barrier between the repelled materials and the surface structure. However, the slippery surfaces in previous studies rarely showed high-temperature resistance. Here, we describe a protocol for the preparation of slippery surfaces with high-temperature resistance. A photolithography-assisted method was used to fabricate pillar structures on stainless steel. By functionalizing the surface with saline, a slippery surface was prepared by adding silicone oil. The prepared slippery surface maintained the anti-wetting property for water, even when the surface was heated to 300 &#176;C. Also, the slippery surface exhibited great anti-adhesion effects on soft tissues at high temperatures. This type of slippery surface on stainless steel has applications in medical devices, mechanical equipment, etc.

Slippery surfaces provide a new way to solve the adhesion problem. This protocol describes how to fabricate slippery surfaces at high temperatures. The results demonstrate that the slippery surfaces showed anti-wetting for liquids and a remarkable anti-adhesion effect on soft tissues at high temperatures.

Anti-adhesion surfaces with high-temperature resistance have a wide application potential in electrosurgical instruments, engines, and pipelines. A ...

Study of Siphon Breaker Experiment and Simulation for a Research Reactor

Under the design conditions of a research reactor, the siphon phenomenon induced by pipe rupture can cause continuous outward flow of water. To prevent this outflow, a control device is required. A siphon breaker is a type of safety device that can be utilized to control the loss of coolant water effectively.
To analyze the characteristics of siphon breaking, a real-scale experiment was conducted. From the results of the experiment, it was found that there are several design factors that affect the siphon breaking phenomenon. Therefore, there is a need to develop a theoretical model capable of predicting and analyzing the siphon breaking phenomenon under various design conditions. Using the experimental data, it was possible to formulate a theoretical model that accurately predicts the progress and the result of the siphon breaking phenomenon. The established theoretical model is based on fluid mechanics and incorporates the Chisholm model to analyze two-phase flow. From Bernoulli&#39;s equation, the velocity, quantity, undershooting height, water level, pressure, friction coefficient, and factors related to the two-phase flow could be obtained or calculated. Moreover, to utilize the model established in this study, a siphon breaker analysis and design program was developed. The simulation program operates on the theoretical model basis and returns the result as a graph. The user can confirm the possibility of the siphon breaking by checking the shape of the graph. Furthermore, saving the entire simulation result is possible and it can be used as a resource for analyzing the real siphon breaking system.
In conclusion, the user can confirm the status of the siphon breaking and design the siphon breaker system using the program developed in this study.

The siphon breaking phenomenon was investigated experimentally and a theoretical model was proposed. A simulation program based on the theoretical model was developed and the results of the simulation program were compared with experimental results. It was concluded that the results of the simulation program matched the experimental results well.

Under the design conditions of a research reactor, the siphon phenomenon induced by pipe rupture can cause continuous outward flow of water. To prevent ...

Predicting Catalyst Extrudate Breakage Based on the Modulus of Rupture

The mechanical strength of extruded catalysts and their natural or forced breakage by either collision against a surface or by a compressive load in a fixed bed are important phenomena in catalyst technology. The mechanical strength of the catalyst is measured here by its bending strength or flexural strength. This technique is relatively new from the perspective of applying it to commercial catalysts of typical sizes used in the industry. Catalyst breakage by collision against a surface is measured after a fall of the extrudates through the ambient air in a vertical pipe. Quantifying the impact force is done theoretically by applying Newton's second law. Measurement of catalyst breakage due to stress in a fixed bed is done following the standard procedure of the bulk crush strength test. Novel here is the focus on measuring the reduction in the length to diameter ratio of the extrudates as a function of the stress.

Here we present a protocol to measure the modulus of rupture of an extruded catalyst and the breakage of said catalyst extrudates by collision against a surface or by compression in a fixed bed.

The mechanical strength of extruded catalysts and their natural or forced breakage by either collision against a surface or by a compressive load in a ...

A 100 KW Class Applied-field Magnetoplasmadynamic Thruster

Applied-field magnetoplasmadynamic thrusters (AF-MPD thrusters) are hybrid accelerators in which electromagnetic and gas dynamic processes accelerate plasma to high speed; they have considerable potential for future space applications with the significant advantages of high specific impulse and thrust density. In this paper, we present a series of protocols for designing and manufacturing a 100 kW class of AF-MPD thruster with water-cooling structures, a 130 V maximum discharge voltage, a 800 A maximum discharge current, and a 0.25 T maximum strength of magnetic field. A hollow tantalum tungsten cathode acts as the only propellant inlet to inhibit the radial discharge, and it is positioned axially at the rear of the anode in order to relieve anode starvation. A cylindrical divergent copper anode is employed to decrease anode power deposition, where the length has been reduced to decrease the wall-plasma connecting area. Experiments utilized a vacuum system that can achieve a working vacuum of 0.01 Pa for a total propellant mass flow rate lower than 40 mg/s and a target thrust stand. The thruster tests were carried out to measure the effects of the working parameters such as propellant flow rates, the discharge current, and the strength of applied magnetic field on the performance and to allow appropriate analysis. The thruster could be operated continuously for significant periods of time with little erosion on the hollow cathode surface. The maximum power of the thruster is 100 kW, and the performance of this water-cooled configuration is comparable with that of thrusters reported in the literature.

The goal of this protocol is to introduce the design of a 100 kW class applied-field magnetoplasmadynamic thruster and relevant experimental methods.

Applied-field magnetoplasmadynamic thrusters (AF-MPD thrusters) are hybrid accelerators in which electromagnetic and gas dynamic processes accelerate ...