EngineeringDesignStructural DynamicsStructural EngineeringVibrationBridge DynamicsDamped VibrationForced VibrationStructural DampingStructural VibrationVibration TestingAcceptance CriteriaDesign CodesPedestrian-induced VibrationsResonant FrequencyResponse SpectrumServiceabilityServiceability Limit StatesStructural Response Spectra
When in use some footbridges vibrate, particularly when the pedestrian footfalls coincide with the first or second mode resonant frequency of the structure. The vibration level may be such that combined with the particular frequency, users find it to be annoying or even alarming. While design codes are now recognising vibration as a serviceability limit state to be investigated, very little information and guidance has been available especially in a form that could be employed as a design tool for structures of general configuration. This paper investigates the subject in its broadest terms, namely the pedestrian excitation source, the structural response, acceptance criteria and remedial options. A test pedestrian is modelled in the walking, jogging and running modes and an adequate, but simplified, dynamic structure model is used in a specialised program to compute the vibration response spectrum. Evaluation of vibrational tendencies then becomes a procedure commensurate with other design routines. Calculated responses compare favourably with the test results from 21 footbridges. A basis for acceptance levels of vibration as a function of frequency, is proposed. The question of remedial action for over lively footbridges is examined in a review of the various forms of damping devices which could be incorporated in both existing and proposed footbridges.