As　a　classical　method　of　physical　parameter　identification,　Extended　Kalman　filtering　(EKF)　algorithm　is　widely　used　in　structural　damage　detection.　However,　due　to　the　complexity　of　the　state　equations,　most　applications　focus　on　the　shear　structure　model　with　translational　degrees　of　freedom　considered　only,　and　the　comprehensive　excitation　and　response　signals　are　generally　needed.　Recognizing　that　the　rotational　degrees　of　freedom　can　be　eliminated　by　the　static　condensation　method,　this　paper　proposes　the　dynamic　condensation　method　considering　Rayleigh　damping,　in　order　to　establish　the　equivalent　and　simplified　model　for　continuous　girder　bridges.　According　to　the　requirements　of　bridge　inspection　and　health　monitoring,　the　online　and　convenient　damage　detection　method　based　on　Extended　Kalman　filtering　is　presented,　and　the　free　vibration　is　generated　by　one　hammer　action,　so　that　the　deficiency　of　the　traditional　method　needing　complex　excitation　information　is　overcame.　Taking　a　three-span　continuous　girder　bridge　as　an　example,　the　corresponding　stiffness,　the　damage　location　and　degree　and　the　damping　parameter　were　identified　accurately　by　the　proposed　method,　showing　that　the　proposed　method,　with　fast　convergence　speed,　is　feasible　for　the　case　of　dynamic　signal　with　high　noise-signal　ratio　and　practical　engineering.　©,　2015,　Tsinghua　University.　All　right　reserved.