Fatigue　tests　on　full-scale　CHS　K-joint　models　have　been　conducted,　exploring　the　distribution　of　hot　spot　stress,　fatigue　crack　development,　and　fatigue　failure　modes.　A　three-dimensional　solid　finite　element　model　has　been　established　to　carry　out　a　parametric　analysis　of　the　main　influences　on　the　stress　concentration　factors　for　CHS　K-joints　using　the　general　software　MSC.MARC.　A　novel　stress　concentration　factor　method　based　on　the　CHS　K-joint　stiffness　has　been　proposed　by　combining　a　theoretical　derivation　and　a　regression　analysis.　The　results　reveal　that　the　hot　spot　stress　of　a　CHS　K-joint　can　be　obtained　with　a　linear　extrapolation.　The　location　of　the　maximum　hot　spot　stress　appears　on　the　crown　toe　point　of　the　chord　and　tensile　brace　intersection　welding　seam　near　the　chord　intersecting　line.　A　fatigue　crack　in　a　CHS　K-joint　belongs　to　the　opening　Class　I　crack　category.　When　the　fatigue　crack　penetrates　the　full　thickness　of　the　chord,　the　fatigue　crack　develops　rapidly;　the　fatigue　failure　of　the　CHS　K-joint　belongs　to　the　brittle　failure　category　in　the　elastic　range.　A　coupling　action　caused　by　the　geometric　parameters　is　demonstrated　to　exist　in　the　stress　concentration　factor　of　CHS　K-joints.　Given　the　current　stress　concentration　factor　method　for　CHS　K-joints　is　based　on　a　regression　analysis　using　a　single　geometric　parameter,　this　limitation　impacts　its　application　in　accurately　in　developing　bridge　structures.　The　novel　stress　concentration　factor　method　encompassing　the　CHS　K-joint　stiffness　proposed　in　this　paper　considers　the　coupling　action　on　the　stress　concentration　factor　caused　by　the　joint　geometric　parameters,　in　addition　to　improving　the　conservativeness　and　accuracy　in　evaluating　and　calculating　the　stress　concentration　factors　of　CHS　K-joints　used　in　bridge　structures.　©　2019