Effect of group walking traffic on dynamic properties of pedestrian structures
Journal of Sound and Vibration
Open Access funded by Engineering and Physical Sciences Research Council Under a Creative Commons license - Attribution 4.0 International (CC BY 4.0)
The increasing number of reported vibration serviceability problems in newly built pedestrian structures, such as footbridges and floors, under walking load has attracted considerable attention in the civil engineering community over the past two decades. The key design challenges are: the inter- and intra-subject variability of walking people, the unknown mechanisms of their interaction with the vibrating walking surfaces and the synchronisation between individuals in a group. Ignoring all or some of these factors makes the current design methods an inconsistent approximation of reality. This often leads to considerable over- or under-estimation of the structural response, yielding an unreliable assessment of vibration performance. Changes to the dynamic properties of an empty structure due to the presence of stationary people have been studied extensively over the past two decades. The understanding of the similar effect of walking people on laterally swaying bridges has improved tremendously in the past decade, due to considerable research prompted by the Millennium Bridge problem. However, there is currently a gap in knowledge about how moving pedestrians affect the dynamic properties of vertically vibrating structures. The key reason for this gap is the scarcity of credible experimental data pertinent to moving pedestrians on vertically vibrating structures, especially for multi-pedestrian traffic. This paper addresses this problem by studying the dynamic properties of the combined human-structure system, i.e. occupied structure damping ratio, natural frequency and modal mass. This was achieved using a comprehensive set of frequency response function records, measured on a full-scale test structure, which was occupied by various numbers of moving pedestrians under different walking scenarios. Contrary to expectations, it was found that the natural frequency of the joint moving human-structure system was higher than that of the empty structure, while it was lower when the same people were standing still. The damping ratio of the joint human-structure system was considerably higher than that of the empty structure for both the walking and standing people – in agreement with previous reports for stationary people - and was more prominent for larger groups. Interestingly, it was found that the walking human-structure system has more damping compared with the equivalent standing human-structure system. The properties of a single degree of freedom mass-spring-damper system representing a moving crowd needed to replicate these observations have been identified.
The authors acknowledge the financial support which came from the UK Engineering and Physical Sciences Research Council (EPSRC) for Platform Grant EP/G061130/2 (Dynamic Performance of Large Civil Engineering Structures: An Integrated Approach to Management, Design and Assessment), responsive mode grants EP/I03839X/1 (Pedestrian Interaction with Lively Low-Frequency Structures), EP/I029567/1 (Synchronization in Dynamic Loading Due to Multiple Pedestrians Occupants of Vibration-Sensitive Structures) and EP/K03877X/1 (Modelling Complex and Partially Identified Engineering Problems - Application to the Individualised Multiscale Simulation of the Musculoskeletal System).
This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.
DOI: 10.1016/j.jsv.2016.10.017 Available online 20th October 2016