Vertical footbridge vibrations: Towards an improved and codifiable response evaluation

An improved and codifiable footbridge response evaluation is presented herewith, in which peak vertical accelerations are provided as a function of load return period in the form of response spectra. To achieve this, a series of Monte Carlo simulations are employed to generate vertical loads induced by a "random" crowd that are subsequently used in linear timehistory analyses of the response of bridges with varying fundamental frequencies. The peak accelerations are presented as a function of return period and it is shown that the acceleration response due to a crowd is lower than $\sqrt{N}$ times the response of a single pedestrian, which is often referred to as a conservative estimate for crowds.