Modal sensitivity analysis of Tsing Ma Bridge for structural damage detection

This study addresses model-based structural damage simulation and identification of the Tsing Ma Suspension Bridge through modal sensitivity analysis. For this purpose, a precise three-dimensional finite element model has been developed with the attributes: (a) the spatial configuration of the original structure remains in the model; (b) the geometric stiffness of cables and hangers has been accurately accounted for in the model; (c) the mass and stiffness contribution of individual structural members is independently described in the model, so damage to any structural member can be directly and precisely simulated. The model was validated using the measured modal data obtained at different erection stages and after the bridge completion. It is then used as a baseline for structural damage simulation and modal sensitivity analysis. Due to the intensive distribution of natural frequencies of the bridge, modal assurance criterion (MAC) is first utilized to check the correlation of mode pairs between the damaged and intact structure. Ten damage cases are simulated and the sensitivities of various modal parameters including natural frequency, mode shape and modal flexibility to different types of damage are evaluated. The goal of this study is to analytically determine which modal parameter is most sensitive to damage for a large-scale suspension bridge. The analysis results show that, in most cases, the frequency sensitivity to damage is low, while the modal flexibility method clearly indicates the damage locations only using a few lowest frequency modes.