Modal Identification of a Pedestrian Bridge by Output-Only Analysis

Abstract

Modal parameters (natural frequencies, mode shapes and damping ratios) describe the dynamic properties of mechanical systems. Classical modal analysis, based on Frequency Response Function, require measurement of both input force and response. Normally, it is very difficult to measure the excitation on large structures (bridges, tall buildings, offshore platforms, etc.). However, reasonable estimates of modal parameters can be extracted from ambient vibration or output-only response (wind, traffic, humans, etc.). The dynamic behaviour of a curved pedestrian bridge in the Cartuja Campus of the Universidad de Sevilla (Spain) has been investigated by full.scale testing and numerical models. Nine vibration modes have been identified in frequency range of 0-30 Hz, by the following algorithms: Enhanced Frequency Domain Decomposition (EFDD) and Estochastid Subspace Identification (SSI)