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

Summary

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.

Abstract

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.

Introduction

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....

Protocol

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

1. 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's charging protocol.
2. MT Manager — Data acquisition²:
   1. Enable the wireless connection with the sensors and specify the desired sample rate (Wireless Configuration &#....

Results

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.......

Discussion

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 'natural' person behavior over many repeated and uninterrupted cycles is currently investigated²⁰. Alter.......

Materials

List of materials used in this article

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