Characterization of stationary and walking people on vertical dynamic properties of a lively lightweight bridge

Abstract

This paper investigates the effect of both stationary and walking people on vertical dynamic characteristics of structures based on an experimental program. A lively lightweight bridge was designed and constructed for the experiments. Dynamic properties of the bridge are obtained based on ambient vibration testing method. Stationary tests of straight knees and bent knees postures under different crowd sizes were performed using heel-impact method. Synchronized walking tests were conducted considering walking frequencies ranging from 1.6 to 2.4 Hz and different group sizes of the participants. Random walking activities were also performed. Results of stationary people tests show a decrease in natural frequency and an increase in damping ratio of the occupied structure with respect to the empty structure as number of people increases, for both straight knees and bent knees postures. However, the structural damping tends to be “stable” (or “saturated”) when number of occupants exceeds a critical value. Theoretical modeling of standing people–structure interaction system reflects similar trend. Results of walking tests also show a decrease in natural frequency and an increase in damping ratio of the structure. Comparison of all test data implies that structural properties, structural weight, load frequency, and crowd size all contribute to structural responses, among which load frequency plays a decisive role. Furthermore, both higher harmonics of walking load and higher vibration modes may contribute remarkably to total structural response for lightweight structures.