Formulation of stress concentration factors for concrete-filled steel tubular (CFST) K-joints under three loading conditions without shear forces

Concrete-filled steel tubular (CFST) K-joints have been widely applied to CFST trussed arch bridges in China, which are comprised of a concrete-filled circular hollow section (CHS) chord and two CHS braces.It has been experimentally revealed that hot spot stress (HSS) of CFST K-joints is significantly lower than those of empty tubular K-joints in the reported researches. However, no parametric formulae on stress concentration factors (SCFs) of CFST K-joints have been established. In present study, three-dimensional FE models for determining the SCF distributions around the chord-brace intersections of CFST K-joints were developed first. The validity of the FE modelling has been examined by comparing with the published experimental results. Then 272 FE models of CFST K-joints with different geometric dimensions were prepared and provided for the parametric study to demonstrate the influence of four key geometric parameters, i.e. diameter ratio (β), diameter to thickness ratio of chord (2γ), thickness ratio (τ) and the angle (θ) between the axis of the chord and brace, on SCFs around the chord-brace intersection. The analysis was performed under three loading conditions, i.e. the basic balanced axial forces, axial compressive force in the chord and in-plane bending in the chord. Finally, parametric formulae to determine the SCFs in CFST K-joints were proposed by the multiple regression analysis, and their accuracy was demonstrated through the comparison of SCFs obtained by the proposed formulae and FEA