Time-varying frequency-based scaled flexibility identification of a posttensioned concrete bridge through vehicle-bridge interaction analysis

Dynamic testing methods have been widely used in engineering practice for investigating dynamic properties of bridges; however, only basic dynamic parameters (i.e., natural frequencies, damping ratios, and unscaled modal shapes) can be identified, which are insufficient for condition assessment and health monitoring. To address this limitation, this article takes a three-span posttensioned concrete bridge as testbed; more useful structural parameters including mass-normalized mode shapes and scaled flexibility matrix are intended to be identified from moving vehicle-induced responses. For identifying scaled flexibility matrix, structural scaling factor between arbitrarily scaled mode shapes and mass-normalized mode shapes needs to be calculated firstly. In this article, time-varying frequencies of vehicle-bridge interaction (VBI) system were adopted for structural scaling factor identification, and the sensitivity of parameters identification error on calculated scaling factor was also investigated. The effectiveness of the proposed method was verified by in situ measurements of the studied three-span concrete bridge. In field testing, static load test and classical impact vibration testing were performed on this bridge for verifying the correctness of the proposed method. The good agreement between predicted deflections by using the scaled flexibility and reference values illustrates the reliability of the proposed method.