A one-way reinforced concrete (RC) slab was subjected to short-duration concentrated impact load and its dynamic characteristic for the virgin and damaged conditions were studied using two signal processing techniques. The recorded strain and acceleration signals were analyzed using the Fast Fourier Transform (FFT) and the Hilbert Huang Transform (HHT). From these analyses, the percentage reductions in the modal frequency for varying degrees of damage (or magnitude of applied load) were obtained. Based on the eigen-solution of a 3-element partitioned beam model, the frequency–damage relationship was also estimated using the observed initial flexural stiffness of the half-cycle hysteresis path associated with each stage of applied load. Both semi-empirical and experimental results showed close agreement and a 30% frequency reduction was observed between the virgin state and yield. Three quarters of the total frequency reduction from virgin-to-yield occurred within an applied load range of 30% of the yield load.

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