A　sensitivity-based　finite　element　(FE)　model　updating　is　carried　out　for　damage　detection　in　this　paper.　The　objective　function　consisting　of　the　modal　flexibility　residual　is　formulated　and　its　gradient　is　derived.　The　optimization　algorithm　used　to　minimize　the　objective　function　and　damage　detection　procedures　are　explained.　The　proposed　procedure　is　firstly　illustrated　with　a　simulated　example　of　the　simply　supported　beam.　The　effect　of　noise　on　the　updating　algorithm　is　studied.　It　is　demonstrated　that　the　behavior　of　proposed　algorithm　on　noise　is　satisfactory　and　the　identified　damage　patterns　are　good.　Afterwards,　the　procedure　is　applied　for　the　tested　reinforced　concrete　beam,　which　is　damaged　in　the　laboratory.　Despite　all　the　elements　in　the　FE　model　are　used　as　updating　parameters　which　is　considered　as　the　extreme　adverse　condition　in　FE　model　updating,　the　identified　damage　pattern　is　comparable　with　those　obtained　from　the　tests.　It　is　verified　that　the　modal　flexibility　is　sensitive　to　damage　and　the　proposed　procedure　of　FE　updating　using　the　modal　flexibility　residual　is　promising　for　the　detection　of　damaged　elements.　(c)　2005　Elsevier　Ltd.　All　rights　reserved.