Vibration-based condition assessments of cables in cable-supported bridges.

摘要

The study presented in this thesis concerns linear and nonlinear vibration analyses and condition assessments of cables in cable-supported bridges.; The linear vibration of large-diameter sagged structural cables is first investigated in this thesis. A three-node curved isoparametric finite element is formulated for dynamic analysis of bridge stay cables by regarding the cable as a combination of an ‘ideal cable element’ and a fictitious curved beam element in the variational sense. The three-dimensional finite element formulation is suited for both suspended and inclined cables and allows for the consideration of cable flexural rigidity, sag-extensibility, spatial variability of dynamic tension, boundary conditions, lumped masses and intermediate spring and/or intermediate dampers. A case study is eventually provided to compare the measured and computed frequencies of cables in a real bridge. The results show that ignoring bending stiffness gives rise to relative errors of 30% in predicting the natural frequencies of the 19th mode. Another case study reveals stiffness effects of attached dampers on the cable frequencies.; The study is then extended to nonlinear oscillation of cables. A hybrid finite element/incremental harmonic balance method is developed for analysis of nonlinear periodically forced vibration of inclined cables with arbitrary sag. The proposed method is an accurate algorithm in the sense that it accommodates multi-harmonic components and no mode-based model reduction is made in the solution process. Both the frequency- and amplitude-controlled algorithms are formulated and are alternatively implemented to obtain complete frequency-response curves including both stable and unstable solutions. The proposed method is also capable of analyzing both super- and sub-harmonic resonances and internal resonances. Case study of applying the proposed method to nonlinear dynamic behaviour analysis of the Tsing Ma Bridge cables is demonstrated. The analysis results show that the side-span free cables of the bridge display distinctly different nonlinear characteristics in the construction and final stages.; Finally, parameter estimation of structural cables is investigated by employing both local and global optimization tools. As an analytical method, the local optimization tools are used to investigate the effects of selection of parameter and weight on the estimation of parameters. (Abstract shortened by UMI.)