Human-structure interaction effect on the dynamic response of footbridges : An analytical and experimental study

Sammanfattning: Lightweight, slender and lightly damped footbridges are often susceptible to HumanInduced Loads (HILs) when pedestrian step frequencies coincide with the naturalfrequencies of the structure. For vertical vibrations, this can compromise the serviceabilitylimit state of the system. The Human-Structure Interaction (HSI) effectoccurs due to the presence of pedestrians that modify the dynamic behaviour ofthe coupled pedestrian-bridge system. Typically, the dynamic analysis of such footbridgesemploys the Finite Element Method (FEM) with stationary harmonic loadingscenarios to assess the dynamic performance of such structures. This researchproject aims to develop a general closed-form solution for the moving harmonic loadproblem (Paper I) using 2D Bernoulli–Euler beam theory for continuous beams onelastic supports. Additionally, it seeks to formulate closed-form solutions for thedynamic amplification factor of the coupled pedestrian-bridge system (Paper II),along with equivalent damping and force models (Paper III) based on response amplitudes.Furthermore, an experimental study of the HSI-effect was conducted onthe Folke Bernadotte Bridge in Stockholm (Paper IV), quantifying the changes ofthe dynamic properties ofthe system and validating the analytical Frequency ResponseFunction (FRF) found in previous studies (Paper II). Finally, the HSI-effectwas studied within the framework of random vibration theory (Paper V) to understandthe expected value of the response of the coupled system using a crowd loadPower Spectral Density (PSD).