Concrete-filled　steel　tubular　(CFST)　columns　are　recognized　for　their　high　load-bearing　capacity,　ductility,　and　energy　dissipation,　primarily　due　to　the　confinement　effect　provided　by　the　steel　tube　on　the　core　concrete.　However,　interface　debonding,　possibly　induced　by　temperature　gradients,　shrinkage,　creep,　or　axial　loads,　can　significantly　compromise　this　performance.　Debonding　can　occur　at　different　severity　levels.　While　severe　debonding　(gap　thicknesses　＞3　mm)　has　been　widely　studied,　the　mechanical　effects　of　moderate　debonding　remain　less　explored.　This　study　investigates　the　role　of　moderate　interface　debonding　through　both　experimental　testing　and　advanced　numerical　modeling.　Five　CFST　short　columns　were　subjected　to　axial　compression　tests.　Debonding　was　introduced　using　stainless　steel　inserts　to　precisely　simulate　various　gap　thicknesses　(0.5　mm　and　1.0　mm)　and　arc-length　ratios　(0.25　and　0.5).　The　results　show　that　even　moderate　debonding　can　reduce　axial　capacity　due　to　early　loss　of　confinement　in　the　concrete　core.　The　study　identifies　three　distinct　response　types　associated　with　moderate　debonding,　depending　on　the　possibility　and　extent　of　steel–concrete　re-engagement.　These　were　further　investigated　through　a　validated　finite　element　model　developed　in　Abaqus　and　benchmarked　against　existing　literature.　A　response　chart　was　established　to　characterize　CFST　performance　as　a　function　of　debonding　thickness　and　arc-length.　The　findings　highlight:　(i)　a　response　comparable　to　fully　bonded　specimens　when　debonding　is　negligible,　(ii)　a　transitional　regime　with　two　distinct　load-bearing　peaks　resulting　from　delayed　confinement　recovery,　and　(iii)　a　degraded　response　with　a　single,　early　peak　and　reduced　ductility　under　larger　debonding　configurations.　The　paper　provides　practical　recommendations　for　evaluating　the　structural　performance　of　CFST　under　moderate　debonding　scenarios.　©　2025　The　Authors