Experimental study of active human-structure interaction during running on footbridges

Abstract

Abstract Slender footbridges are predominantly sensitive to human-induced vibrations. While the previous two decades have focussed on pedestrian-induced vibrations, topical research questions are investigating the impact of running actions. The currently available load model for vibration serviceability assessments only applies to a single runner on a rigid surface. The present work investigates whether low-frequency vertical vibrations of the supporting surface affect the running motion, known as active human-structure interaction. To facilitate characterisation, an extensive measurement campaign was organised. First, a treadmill was placed on a rigid surface as reference and secondly on a vibrating footbridge, excited by a mechanical shaker. The measurement setup enables the simultaneous registration of the contact forces, body motion, running motion metrics on a step-by-step basis and the structural response. The results indicate that human-structure interaction phenomena do occur while running on a vertical vibrating surface. The main effects include changes of the peak contact force, determined by the relative phase between the body motion and the footbridge’s motion. Moreover, when running (near) resonance, two stable running regimes can occur. The first resembles a non-resonant runner (constantly alternating between in- and out-of-phase) while the second resembles resonant running by keeping a fairly constant phase with the structure.