Damping Estimation from Full-Scale Traffic-Induced Vibrations of a Suspension Bridge

We present an automatic technique for structural damping estimation, based on traffic-induced vibrations of a long-span suspension bridge. First, an identification algorithm is applied to the acceleration data of the Lysefjord Bridge to capture traffic load events, i.e. when vehicles are crossing the bridge. Thereafter, a time domain decomposition is adopted to compute the modal displacement response triggered by the traffic excitation. The damping ratio and the eigenfrequency are then estimated by fitting a single degree-of-freedom system to the modal response. The damping estimates exhibit a lower dispersion and bias than the corresponding results based on a covariance driven stochastic subspace identification algorithm. Estimating damping ratios using traffic-induced decays removes the problems of frequency resolution for short-length records and may, therefore, complement other ambient vibration identification techniques.