Dynamic characteristics of a curved cable-stayed bridge identified from strong motion records

An assessment of dynamic characteristics of the 455 in Katsushika-Harp curved cable-stayed bridge is presented. Dynamics characteristics such as natural frequencies, mode shapes and modal damping ratios are obtained from seismic response of the bridge by employing a time-domain multi-input multi-output (MIMO) system identification (SI) technique. The technique makes use of base motions and superstructure accelerations as pairs of inputs-outputs to realize the coefficients of state-space system matrices. The SI results indicate the occurrence of many closely spaced modal frequencies with spatially complicated mode shapes. Fourteen global modes in the ranges of 0.45-2.5 Hz were identified, in which the girder motion dominated most of the modes. The tower modes were associated with girder modes and were characterized by the lowly-damped motion. Using identification results from six earthquakes, the effects of earthquake amplitude on modal damping ratios were observed. (c) 2006 Elsevier Ltd. All rights reserved.