The　external　restraining　members　in　an　Assembled　Buckling-Restrained　Brace　(ABRB)　are　mainly　connected　by　high-strength　bolts.　Because　of　the　bolts＇　longitudinal　discrete　layout,　the　stiffness　reduction　of　the　external　restraining　members　should　be　considered,　and　a　significant　increase　in　the　local　stress　of　the　external　member　between　two　bolts　must　be　considered　as　well.　Thus,　this　study　first　uses　theoretical　derivation　and　numerical　verification　to　investigate　the　stress　state　of　BRB　subjected　to　core　single　wave　overall　deformation　and　core　multi-wave　buckling　deformation,　respectively.　Based　on　the　unique　mechanical　characteristics　of　the　pinned　ABRBs,　a　design　method　applicable　for　the　pinned　ABRB　with　a　flat　core　is　put　forward,　considering　the　external　restraining　stiffness　reduction　coefficient　and　the　additional　local　influence　of　contact　force　when　the　core　deforms　in　a　multi-wave　form.　Finally,　six　ABRB　FE　models　are　presented　to　verify　the　rationality　of　the　design　method　being　safe　and　reliable　to　predict　the　ABRB＇s　overall　buckling　failure　and　bending　failure　in　the　ECSR　of　BRBs.　This　design　method　also　considers　the　influence　of　a　series　of　design　parameters,　including　the　gap　between　the　core　and　external　members,　pinned　connector　length,　extended　core　length,　length,　strength,　stiffness　and　imperfection　of　the　external　restraining　members,　bolt　dimensions　and　layout,　etc.　(C)　2016　Elsevier　Ltd.　All　rights　reserved.