Abstract: In a recent series of laboratory tests, a novel laser Doppler vibrometer (LDV) was used to determine the stiffness degradation of concrete columns subjected to ever- increasing, reversed cyclic loads. As a rule, the stiffness degradation of concrete structures due to earthquake-induced damage is obvious in most circumstances. Unfortunately the visual inspection of those columns subjected to flexural failure in the laboratory did not heuristically convey the same impression of stiffness degradation as a detailed experimental modal analysis survey. Some 'failed' columns only exhibited minor surface cracks. There are several techniques to assess damage in 'failed' concrete structures; the natural frequency determination technique is one of them. As expected, an experimental modal analysis confirmed that the natural frequencies of each concrete column decreased as more damage was induced. Thus, a structure's stiffness degradation can be determined by comparing its pre- and post-damage natural frequencies. As an alternative to the experimental modal analysis, we report on the concrete columns' stiffness degradation from a series of flexural and shear strength test using a novel LDV. Two significant advantages of using the LDV in this application are: (1) the method is non-obtrusive and (2) the instrumentation required is minimal. !1
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