A serviceability analysis of pedestrian induced excitation of light-weight FRP footbridges

Abstract

Over the past 8 years icubed consulting have been developing in-house software and procedures on the excitation performance of Fibre Reinforced Polymer (FRP) pedestrian footbridges. icubed had concerns with pedestrian induced excitation performance due to the lightweight nature of FRP structures and devised a method to assess accelerations in accordance with international research and backed this up with in-situ testing. A pulsating force load was produced using Fourier Transformation equations to replicate the vertical and horizontal impact of a footfall load. This load was applied at to the deck in a 3D model and factored using formula to evaluate the effect of multiple pedestrians walking in-sync and out-of-sync across the structure. A transient solver produced graphs of maximum nodal accelerations under various pedestrian cases which were then compared to acceleration limitations outlined in other literature. icubed discovered that some in-sync load cases could amplify deck accelerations by a considerable amount. Further investigation into excitation was undertaken with in-situ testing. Deck acceleration data was collected using an Android smartphone to compare theoretical models against actual in-situ performance. icubed also investigated the dynamic wind excitation of these structures using British Standards and open-source Computational Fluid Dynamics (CFD) software OpenFOAM. The software models a 2D cross section of the pedestrian bridges to undertake a sensitivity analysis for the critical wind velocity that may cause the structure to self-excite.