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Change in Impact-Echo Response during Fatigue Loading of Concrete Bridge T-Girder

Concurrent with full-scale fatigue load tests, impact-echo tests were performed for nondestructive condition change assessment for a T-shaped reinforced concrete bridge with aspect ratios of B/D = 1.08, D/b = 2.33, and B/t = 5.1. Initial girder condition and six subsequent fatigue loading interval conditions were assessed through cross-sectional vibrational mode analysis and apparent P-wave velocity changes. For the initial girder condition, the first three cross-sectional vibration modes were determined to be 1,820, 2,900, and 3,800 Hz. A cross-sectional mode frequency shift and new peak appearance in the damage wave reflection corresponding response spectra indicated fatigue loading damage. The highest damage level observed was for tests located in the loading plate vicinity and correlated well with visual cracking observations on the exterior girder surface.