Bridges

Footbridges are, by their nature, highly susceptible to human-induced vibrations as they may combine low levels of damping, low natural frequencies and low mass. Due to the increased flexibility and lightness of modern footbridges, dynamic forces can cause larger amplitudes, therefore, it is essential to pay greater attention to structural vibration and dynamic responses. The natural frequencies, damping properties, bridge mass and pedestrian loading, together, determine the dynamic response. The vibration behaviour caused by pedestrian traffic must be confirmed against the vibration monitoring and correlate with the design parameters. Then, it must be compared against the required human comfort standards and guidelines. If the vibration responses do not meet the comfort criteria, changes in the design or damping devices are advised.

This paper presents the ambient modal testing and human-induced load tests for one in-service pedestrian bridge in Melbourne, Australia. The relevant modal parameters were extracted, and the vibration serviceability limit state (VSLS) was assessed with the Eurocodes and the AS 5100 , including relevant guidelines such as HIVOSS and SETRA. ISO 2631-1 and AS 2670-1 provide appropriate frequency weighting functions based on the vibration direction since the sensitivity of the human body to vibration is frequency and direction dependent. These weighting functions apply only to stationary humans. ISO 101373 differentiates between moving and stationary pedestrians providing multiplying factor criteria for each scenario. Vibration predictors have been evaluated using both frequency weighted and unweighted functions and the results have been assessed against the use of these functions at dominant, relevant frequency responses of the footbridge.