To detect internal horizontal cracks in RC slabs of bridge structures, this paper proposes stimulating and measuring vibration of a plate consisting of concrete on the upper part of the internal horizontal crack of the RC slab. Giving enforced sweeping vibration from the RC surface and/or the asphalt pavement surface, both natural frequencies and mode shapes about the crack part are measured and compared with the corresponding theoretical ones. Their agreement implies applicability of the proposed method to detect the internal horizontal crack in RC slabs as one of the feasible non-destructive inspections in fields.
