Parametric Analysis and Design Formulas for Circular Hollow Section KK′X Joints

Abstract:

Parametric analysis for the ultimate bearing capacity （UBC） of multiplanar KK′X gap joints in circular hollow section （CHS） trusses is conducted using the finite element （FE） model validated by tests. The study reveals that τ_K and τ_X have minimal impact on the UBC of the joints， whereas other geometric parameters exert a greater influence. UBC of K-brace significantly decreases with the increase of axial force in the X-brace. The axial compressive force in the chord member adversely affects the UBC， while axial tension has little impact. Based on the calculation formulas for UBC of uniplanar K-joints in design standard of steel structures， the formula for UBC of multiplanar KK′X joints subjected to axial force on K-brace with chord plasticization failure is proposed by means of geometric adjustment coefficient μ_KKX and influence coefficient ψ_m considering the ratio of axial force between braces. The accuracy of this formula has been validated by FE analysis and experimental data. Using the calibration method prescribed in design standard of steel structures， a design formula for UBC of multiplanar CHS KK′X joints is finally recommended， providing a practical design guideline for the engineering application of this type of complicated tubular joints.