Most　of　vibration-based　damage　detection　methods　require　the　modal　properties　that　are　obtained　from　measured　signals　through　the　system　identification　techniques.　However,　the　modal　properties　such　as　natural　frequencies　and　mode　shapes　are　not　such　a　good　sensitive　indication　of　structural　damage.　The　wavelet　packet　transform　(WPT)　is　a　mathematical　tool　that　has　a　special　advantage　over　the　traditional　Fourier　transform　in　analyzing　non-stationary　signals.　It　adopts　redundant　basis　functions　and　hence　can　provide　an　arbitrary　time-frequency　resolution.　In　this　study,　a　damage　detection　index　called　wavelet　packet　energy　rate　index　(WPERI),　is　proposed　for　the　damage　detection　of　beam　structures.　The　measured　dynamic　signals　are　decomposed　into　the　wavelet　packet　components　and　the　wavelet　energy　rate　index　is　computed　to　indicate　the　structural　damage.　The　proposed　damage　identification　method　is　firstly　illustrated　with　a　simulated　simply　supported　beam　and　the　identified　damage　is　satisfactory　with　assumed　damage.　Afterward,　the　method　is　applied　to　the　tested　steel　beams　with　three　damage　scenarios　in　the　laboratory.　Despite　the　noise　is　present　for　real　measurement　data,　the　identified　damage　pattern　is　comparable　with　the　tests.　Both　simulated　and　experimental　studies　demonstrated　that　the　WPT-based　energy　rate　index　is　a　good　candidate　index　that　is　sensitive　to　structural　local　damage.　©　2005　Elsevier　Ltd.　All　rights　reserved.