Hilbert-Huang transform (HHT) technique and wavelet transform technique are applied to the detection of damage locations in several civil infrastructures. The HHT and wavelet methods may be used to identify the locations of damages which exhibit nonlinear and non-stationary behavior, since the instantaneous frequency characteristics of the measured signals can be analyzed by those methods. Numerical simulations were conducted on two bridge systems with damages using controlled excitations with sweeping frequency. Bilinear model using a gap element is employed to model the behavior of cracked elements in the numerical simulations. The results indicate that the HHT method can reasonably identify the damage locations based on a limited number of acceleration sensors. Experimental study has been also carried out on a steel frame to confirm the applicability of the HHT to detect the structural connection with loosened bolts.