Pedestrian-induced vibrations on footbridges: advanced response analysis

Pedestrian-induced vibrations (PIV) on footbridges, overpasses, and floors are attracting more attention to the designers and are becoming as important dynamic excitation to consider as wind and earthquake. A key reason for this trend is the public awareness and higher performance standards set on new projects where better comfort is sought and lively structures are less tolerated. At the same time, more efficient material utilization and new construction methods are producing more efficient structures with less capability to dissipate the energy input (low damping) and as a result, are more sensitive to dynamic excitations. In addition, recent research has led to an improved understanding of the pedestrian vibration problem and with the advances in both practical and refined analytical methods, designers may better determine what vibration control measures are appropriate for an optimized design. This paper presents the basics of the PIV problem and a new method for direct time domain simulations of PIVs that allows rather realistic evaluation of a bridge's dynamic performance and evaluation of comfort to its users. Based on statistical distributions of key parameters such as gait frequency, phase and length, personal weight and type of activity, a wide variety of loading scenarios may be readily evaluated. Most importantly, the hypothesis of 'lock-in' can be verified, which allows less conservative response estimates derived from methods based on formulae that assume post lock-in conditions. A brief discussion on vibration control is also included.