A load–deformation formulation for CHS X- and K-joints in push-over analyses

• We propose a new nonlinear formulation to CHS X- and K-joints.
• This formulation describes the peak and post-peak responses of the joints.
• The proposed formulation derives from calibrated FE analyses for X- and K-joints.
• This formulation predicts accurately the failure mechanisms in 2D and 3D frames.

This paper proposes a new load–deformation formulation for circular hollow section (CHS) X- and K-joints to be implemented in the pushover analysis of steel frames. The proposed formulation describes the load–deformation relationship of the CHS X- and K-joint through a simple function with the coefficients dependent on the ultimate strength and the geometric parameters of the joint. The strength-dependent parameter follows the mean strength equations in the latest IIW recommendations, while the geometric-dependent parameters derive from the finite element results of the CHS X- and K-joints covering a practical geometric range. The proposed joint formulation predicts closely the load–deformation responses for planar CHS X- and K-joints measured in the experiments. The non-dimensional load–deformation formulation developed in the current study provides a calibrated basis in the phenomenological representation of the nonlinear joint behavior in push-over analyses of steel space frames. The experimental results from the large-scale 2-D and 3-D frame tests validate the accuracy of the proposed formulation, which is implemented in a nonlinear pushover analysis as joint-spring elements.