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A nondestructive test method called impact-echo is under de-
velopment for locating flaws in concrete using transient stress
waves. To date, the method has been used succesfully to find
flaws in plate-like structures. Applications of the method to
circular, square and rectangular columns have been accomplished
numerically and experimentally. In this thesis, laboratory re-
sults detecting single cracks in a concrete slab is presented
first. In addition, two overlapped cracks with different sizes
were also embedded in the slab to study whether the impact-echo
method can be used to detect multiple cracks. It is shown that
when the crack closer to the impact surface is smaller than the
other crack, both of them can be detected simultaneously. It is
suggested that tests can be performed on all accessible
surfaces to locate multiple flaws in concrete structures. The
signal ana- lysis of the impact-echo is exclusively based on
measuring the surface displacement response of a test object
subjected to point impact. In this study, a comparison of
spectra transformed from displacement, velocity, and
acceleration waveforms was made numerically as well as
experimentally to locate accurately sha- llow flaws. These
studies were aimed at determining the feasibi- lity of using
different types of transducers in the impact-echo testing
system.
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