Damage Detection Strategy Using Strain-Mode Residual Trends for Long-Span Bridges

In this paper, a damage detection strategy based on distributed strain responses measured by long-gauge fiber Bragg grating (FBG) sensors is investigated. First, the distributed strain modes of a system with multiple degrees of freedom (DOFs) are derived via the frequency response function (FRF) of distributed strain response. Then the distributed strain mode is used to identify different degrees of damage incurred in a long-span, cable-stayed bridge under ambient excitation. The robustness of the distributed strain mode for detecting damage is analyzed, and it is found that its robustness is affected by ambient excitation, mode normalization, degree of damage, and noise pollution. To improve the robustness of the distributed strain-mode method, a damage detection strategy based on distributed strain-mode residual trends is developed using statistical tendency analysis and confidence probability. Finally, a numerical analysis is performed on the bridge structure under different operational conditions. The analytical results show that the proposed strategy can reduce the effects of loading variability and environmental diversity on the identified strain mode and locate damage accurately with good damage severity assessment and a high level of robustness. (C) 2014 American Society of Civil Engineers.