The　failure　modes　of　K-joints　of　Concrete　Filled　Steel　Tubular　(CFST)　truss　structures　were　investigated　through　laboratory　tests.　CFST　K-joint　specimens　consisted　of　a　tubular　chord　filled　with　concrete　and　two　braces　inclined　at　the　same　angle　with　respect　to　the　chord.　Their　size　was　chosen　of　the　same　scale　as　that　of　joints　of　real　tubular　structures　currently　used　in　bridges.　The　results　were　compared　with　those　obtained　by　testing　K-joint　specimens　of　Circular　Hollow　Section　(CHS)　truss　structures　with　the　same　size.　Contrary　to　CHS　K-joints,　where　a　chord　face　failure　mode　occurred,　in　CFST　K-joints　no　failure　mode　with　inward　deformation　of　the　chord　section　can　occur.　Hence,　punching　shear　failure　was　shown　to　be　the　typical　failure　mode　of　CFST　K-joints,　if　no　brace　failure　mode　occurred　before.　Resistance　of　CFST　K-joints　to　punching　shear　was　then　compared　with　the　resistance　values　calculated　through　the　Eurocode　3　and　the　AWS　code　formulae　on　CHS　K-joints.　The　values　provided　by　the　former　formula　were　quite　close　to　(although　always　lower　than)　the　actual　resistance　to　punching　shear　of　CFST　K-joints.　Finally,　the　favourable　effect　on　joint　resistance　due　to　additional　studs　welded　to　the　interior　surface　of　the　chord　tube　of　CFST　K-joint　was　also　investigated.　(c)　2015　Elsevier　Ltd.　All　rights　reserved.