Evaluation of design requirements for footbridges excited by vertical forces from walking

Abstract

The continuing trend towards the design of more slender, lighter, and livelier footbridges has created new challenges that are not properly addressed in a number of widely used codes of practice in Europe and Canada. Recent research into vibration serviceability of slender structures under human-induced dynamic loading suggests that improvements to the existing footbridge design guidelines are possible in the area of modelling human-induced excitation in the vertical direction. This paper evaluates the performance of currently used codes of practice regarding vibration serviceability of footbridges under human-induced loads due to walking. The evaluation is supported by experimental evidence from tests carried out by the authors on potentially lively footbridges. A description of recent research advances is included, together with a comparative analysis of the approaches of some pertinent guidelines used internationally to tackle this design problem. In addition, suggestions are made for re-addressing the problem of vibration serviceability of footbridges by focusing attention on a more realistic definition of vertical pedestrian loading and the corresponding frequency ranges of interest. It was found that the codes are either conservative or lack appropriate safety margins, depending on the frequency range excited by moving pedestrians. This is principally due to the lack of proper consideration for the frequency content of the pedestrian load, which would take into account developments since the 1970s when the scientific data used in the majority of the current codes of practice were produced.Key words: vibration, serviceability, walking, footbridges, design, codes, dynamic loading factor, evaluation.