The　ultrahigh-performance　concrete　(UHPC)-encased　concrete-filled　steel　tubular　(CFST)　column　(referred　to　as　UC-CFST　column)　is　a　novel　composite　structure　that　fully　leverages　the　outstanding　material　properties　of　UHPC,　effectively　addressing　issues　such　as　poor　corrosion　resistance　and　durability　commonly　found　in　ordinary　concrete-encased　CFST　column　(referred　to　as　an　OC-CFST　column).　To　study　the　shear　behavior　of　UC-CFST　columns,　shear　tests　were　conducted　on　20　specimens,　comprising　four　CFST　stub　columns,　three　UHPC　stub　columns,　four　OC-CFST　stub　columns,　and　nine　UC-CFST　stub　columns,　respectively.　The　influence　of　the　strength　and　area　ratio　of　the　encasing　material　on　the　shear　behavior　and　failure　modes　of　UC-CFST　stub　columns　was　studied.　Concurrently,　a　nonlinear　finite-element　model　of　UC-CFST　stub　columns　was　established,　allowing　for　an　in-depth　analysis　of　the　shear　resistance　mechanisms　of　such　novel　composite　structures.　Based　on　the　actual　bridge　dimensions,　a　finite-element　parameter　analysis　was　conducted　to　study　the　effects　of　encasing　material　strength　and　area　ratio.　The　results　indicated　that　OC-CFST　stub　columns　exhibited　ductile　failure　characteristics,　whereas　UC-CFST　stub　columns　demonstrated　brittle　failure　characteristics.　Compared　with　OC-CFST　stub　columns,　UC-CFST　stub　columns　showed　significant　improvements　in　shear　stiffness　and　shear　capacity,　with　better　synergistic　deformation　capabilities　between　the　outer　layer　of　reinforced　UHPC　and　the　core　CFST.　When　the　outer　diameter　of　the　steel　tube　was　kept　constant,　the　shear　capacity　of　UC-CFST　stub　columns　increased　with　the　area　ratio.　However,　when　the　outer　diameter　of　the　composite　column　was　kept　unchanged,　the　shear　capacity　of　UC-CFST　stub　columns　first　decreased　and　then　increased　with　an　increasing　area　ratio.　Finally,　drawing　on　existing　standards,　a　formula　for　calculating　the　shear　bearing　capacity　of　UC-CFST　stub　columns　has　been　proposed　using　the　truss-arch　model.　The　calculated　results　demonstrate　a　strong　alignment　with　the　experimental　outcomes.　©　2025　American　Society　of　Civil　Engineers.