Case histories are presented to illustrate the use of modal analysis and testing techniques for nondestructive testing and evaluation (NDT&E) investigations of civil engineering structures. The modal analysis is based on the behavior of stress waves generated in the structures. The stress wave measurements from modal impulse response (IR) tests provide data on dynamic properties that are directly and indirectly related to physical conditions of the structures. Case histories discussed include IR results from sound and defective deep foundations, slabs with good subgrade and void support conditions, and forensic quality assurance testing of repairs of a concrete box girder bridge.
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