Footbridge system identification using wireless inertial measurement units for force and response measurements

James Brownjohn, Mateusz Bocian, David Hester, Antonino Quattrone, William Hudson, Daniel Moore, Daniel Moore, Sushma Goh, Meng Sun Lim

Research output: Contribution to journalArticlepeer-review

26 Citations (Scopus)
227 Downloads (Pure)


With the main focus on safety, design of structures for vibration serviceability is often overlooked or mismanaged, resulting in some high profile structures failing publicly to perform adequately under human dynamic loading due to walking, running or jumping. A standard tool to inform better design, prove fitness for purpose before entering service and design retrofits is modal testing, a procedure that typically involves acceleration measurements using an array of wired sensors and force generation using a mechanical shaker. A critical but often overlooked aspect is using input (force) to output (response) relationships to enable estimation of modal mass, which is a key parameter directly controlling vibration levels in service.

This paper describes the use of wireless inertial measurement units (IMUs), designed for biomechanics motion capture applications, for the modal testing of a 109 m footbridge. IMUs were first used for an output-only vibration survey to identify mode frequencies, shapes and damping ratios, then for simultaneous measurement of body accelerations of a human subject jumping to excite specific vibrations modes and build up bridge deck accelerations at the jumping location. Using the mode shapes and the vertical acceleration data from a suitable body landmark scaled by body mass, thus providing jumping force data, it was possible to create frequency response functions and estimate modal masses.

The modal mass estimates for this bridge were checked against estimates obtained using an instrumented hammer and known mass distributions, showing consistency among the experimental estimates. Finally, the method was used in an applied research application on a short span footbridge where the benefits of logistical and operational simplicity afforded by the highly portable and easy to use IMUs proved extremely useful for an efficient evaluation of vibration serviceability, including estimation of modal masses.
Original languageEnglish
Pages (from-to)339-355
Number of pages17
JournalJournal of Sound and Vibration
Early online date20 Aug 2016
Publication statusPublished - 08 Dec 2016


  • Footbridge vibration; Human jumping; Modal mass identification; Wireless sensor


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