Mechanical behaviour and design of concrete-filled K and KK CHS connections

Abstract The mechanical behaviour of concrete-filled K and KK circle hollow section (CHS) connections are assessed experimentally and numerically in this paper. Three large-scale concrete-filled K and KK connections were tested. The experimental stress concentration factor (SCF) values of the KK connection were compared with the predictions calculated using the current design specifications. The finite element (FE) models were developed and validated against the current and previous test results. Based on the developed models, the parametric study was conducted to study the influence of the two pairs of K-braces and the axial compressive force of the chord on the punching shear stress distribution and ultimate strength. The applicability of the design specifications intended for the design of pure steel CHS connections and the previously proposed design equation for concrete-filled T and Y CHS connections to the concrete-filled K- and KK-type connections were evaluated. Both experimental and numerical results demonstrated that the concrete-filled CHS connection failed at punching shear fracture on the chord-wall near the weld toe. The interaction between two K-pairs should be considered in the strength design, and the level of the chord compressive load should be controlled to avoid the occurrence of the combined failure mode. The proposed design methods for K and KK connections can predict the punching shear strength of concrete-filled K and KK connections with reasonable accuracy.