On damage detection of beam structures using multiple types of influence lines

Damage indices that are sensitive to early damage or abnormality of bridges are essential to take protective measures before any catastrophic failure of bridges occurs. Influence lines (ILs) have been proved as a promising bridge damage index numerically and experimentally. However, a comprehensive study on using various types of ILs for damage detection is still unavailable. This paper explicitly reveals the intrinsic relationships among various types of ILs, including deflection, rotation, bending stress, and shear stress ILs, and their corresponding first-and second-order finite differences with respect to moving force locations. Subsequently, the sensitivities and detectable ranges of various types of ILs are investigated and compared systematically through two representative examples, namely, a simply supported beam and a continuous beam. The sensor locations that correspond to high sensitivities and wide detectable ranges are identified for various types of ILs. The pros and cons of calculating the finite differences of ILs for damage detection are also illustrated with consideration of measurement noise. An experiment on a simply supported beam was conducted to partially validate the findings in this study. The conclusions of this study answer fundamental questions regarding the rational selections of IL types and sensor locations in IL-based damage detection methods.