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Characterisation of crowd lateral dynamic forcing from full-scale measurements on the Clifton Suspension Bridge

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journal contribution
posted on 02.04.2020, 08:22 by RE White, NA Alexander, JHG Macdonald, M Bocian
Lateral loading of bridges by a crowd of walking pedestrians is of serious concern as it can lead to a sudden growth in the amplitude of structural oscillations, i.e. lateral dynamic instability. A vibration amplitude threshold, marking a qualitative change in pedestrians’ behaviour, is then usually proposed beyond which the likelihood of structural instability is said to increase. To verify this presumption, measurements were taken during a crowd loading event on Clifton Suspension Bridge in Bristol, UK. Two lateral modes of the bridge were studied, previously found susceptible to pedestrian-induced excitation. A novel procedure is proposed based on time-frequency analysis enabling, for the first time, the average equivalent added mass per pedestrian to be identified from measurements on a full-scale structure. Previous measurements on Clifton Suspension Bridge during crowd loading leading to the onset of large-amplitude vibrations revealed an increase in the natural frequency of one from the two considered modes. The proposed time-frequency analysis procedure has successfully identified the additional mass, due to the pedestrians, that is effectively negative. Cycle-by-cycle energy analysis per mode confirms the presence of additional damping of the pedestrians at low vibration amplitudes, that is also effectively negative. Although some of the results are uncertain quantitatively, there is no evidence of the amplitude threshold at which the human-structure interaction phenomenon occurs.

Funding

The authors gratefully acknowledge: the Clifton Suspension Bridge Trust for the research opportunity and cooperation throughout installation and decommissioning of the Structural Health Monitoring System; the Bridgemaster Mrs. Trish Johnson and the bridge maintenance staff for their assistance; Mr. Sam Gunner for the installation and decommissioning of his bespoke Structural Health Monitoring System; Miss Xioyang Wang, Dr. Ute Leonards and Mr. Artur Soczawa-Stronczyk for assisting in the data collection; Dr. Matt Dietz for consultation on data processing and spectral analysis, COWI for providing details of their Finite Element model and EPSRC funding under grant no. EP/P016782/1. RW is supported by an EPSRC Doctoral Training Partnership studentship.

History

Citation

E. White, N.A. Alexander, J.H.G. Macdonald, M. Bocian, Characterisation of crowd lateral dynamic forcing from full-scale measurements on the Clifton Suspension Bridge, Structures, Volume 24, 2020, Pages 415-425

Version

AM (Accepted Manuscript)

Published in

Structures

Volume

24

Pagination

415 - 425

Publisher

Elsevier BV

issn

2352-0124

eissn

2352-0124

Acceptance date

29/11/2019

Copyright date

2020

Available date

04/02/2020

Publisher version

https://www.sciencedirect.com/science/article/pii/S2352012419302097

Notes

Data are available at the University of Bristol data repository, data.bris, at https://doi.org/10.5523/bris.1y1ajsjpkpzom2qt10eg6pnjo0.

Spatial coverage

Bristol, UK

Language

en