Multimode-based evaluation of cable tension force in cable-supported bridges

For the purpose of developing a precise parameter identification procedure for bridge cables using measured multiple-mode parameters, a systematic investigation on the modal properties of cables is first carried out by using a three-dimensional finite element formulation taking into account the cable flexural rigidity, sag-extensibility, and non-constant dynamic tension force. The dimensionless frequencies are evaluated for free vibration of cables with their parameters lying in a wide range covering most of the cables in existing cable-supported bridges. The relation surfaces between the dimensionless frequencies and structural parameters are obtained for both lower and higher modes. Based on the systematic analysis of cable modal properties, a nonlinear least-squares method is then adopted to evaluate cable tension force by use of measured multiple-mode frequencies. The statistical processing method of identified cable tension forces under different noise levels is addressed. The importance and effect of specific high-order frequencies on the identification accuracy are discussed. It is expected that after some further extension, the proposed procedure can serve as a tool for evaluating cable tension force with high accuracy and reliability.