Damage　detection　of　real-life　civil　structures　is　generally　performed　under　a　condition　of　poor　information,　mainly　referring　to　our　insufficient　knowledge　of　structures,　uncertainties　and　limited　sensors.　Moreover,　most　damage　detection　methods　require　the　numerical　or　mathematical　models　of　a　structure,　whose　stiffness　parameters　are　sought　by　inverse　solutions　such　as　model　updating.　However,　ill-conditioning　problems　are　often　found　when　updating　complex　structures.　Hence,　a　model-free　damage　localization　strategy　has　been　proposed　incorporating　wavelet　packet　transform　with　grey　relation　analysis.　First　acceleration　response　signals　are　decomposed　into　different　frequency　subbands　using　wavelet　packet　transform.　The　wavelet　packet　energies　of　specific　frequency　subbands　corresponding　to　fundamental　modal　frequencies　are　extracted　and　then　normalized　by　the　total　energy　of　all　the　accelerometers.　After　that,　wavelet　packet　energy　curvatures　are　constructed　and　incorporated　with　grey　relation　analysis　to　propose　a　wavelet　grey　correlation　coefficient.　Damage　locations　are　determined　according　to　magnitude　changes　in　these　coefficients.　Lastly,　the　feasibility　of　the　proposed　method　has　been　successfully　verified　against　an　experimental　steel　beam.　The　validation　also　found　that　direct　damage　localization　based　on　mode　shapes　or　modal　curvatures　could　not　provide　effective　judgment.　©　2020　IOP　Publishing　Ltd.