Ambient vibration testing, system identification and model updating of a multiple-span elevated bridge

This paper presents ambient-vibration based investigations conducted on the Newmarket Viaduct, a 12 span, 690m long, curved, segmental, elevated, post-tensioned concrete viaduct located in Auckland, New Zealand, to assess the dynamical behavior of the bridge during construction. The assessment procedure included full-scale ambient vibration testing, modal identification from ambient vibration responses using two different output-only identification methods, finite element (FE) modelling and sensitivity-based model updating-based identification of the uncertain structural parameters of the model. Ambient tests were conducted for the accurate estimation of the dynamic characteristics using Enhanced Frequency Domain Decomposition and Stochastic Subspace Identification. An initial 3D FE model was then developed from the information provided in the design documentation of the bridge. The output-only modal identification results from ambient vibration measurements of the bridge were subsequently used to update the FE bridge model. Different parameters of the model were modified using an automated procedure to improve correlation between the measured and calculated modal parameters. Careful attention was placed on the selection of the parameters to be modified by the updating procedure in order to ensure that the necessary changes are realistic and physically meaningful. A very good match between theoretical and experimental modal parameters was reached. The calibrated FE model reflecting the as-built structural conditions of the bridge will serve as a baseline model for the assessment of structural health using continuous monitoring data.