Modal indices for identifying damage location in cable-stayed Kap Shui Mun Bridge

This paper presents a comparative study of using the modal curvature index and the modal flexibility index for damage localization in the cable-stayed Kap Shui Mun Bridge from the bridge global modal data before and after damage. Based on a precise and validated three-dimensional finite element model of the bridge, a series of damage cases associated with the deck are introduced in the simulation study. They are the damage occurring at the members within deck segments and the damage occurring at the support and bearing system of the deck. The damage indices are applied to determine the specific deck segment that contains damaged member(s). The simulation study is conducted with the following focuses: (i) performance comparison of the two indices in the absence of noise; (ii) tolerance of the two indices to noise; (iii) influence of the number of measured modal vectors on the identification accuracy of the two indices. The analysis results show that performance of the two indices is different for different damage types. The two modal indices are complementary to each other in damage indication. In general the flexibility index performs better than the curvature index for damage indication, especially in the case of damage occurring at the bearing system. For most damage cases, the flexibility index is better in anti-noise than the curvature index, and the curvature index is more sensitive than the flexibility index to the number of the measured modal vectors (degree of the modal incompleteness).