Numerical study on seismic behaviours of ConXL biaxial moment connection

• An accurate nonlinear finite element model of ConXL connection is established using ABAQUS software.
• Four representative kinds of joint forms—2D interior, 3D interior, 3D exterior, and 3D corner—are simulated.
• Failure modes under different axial loads are determined.
• The hysteretic behavior is compared with the equivalent loading-displacement relationship at column top.

The ConXL connection is a standardized and cost-efficient biaxial moment frame connection. It could provide higher construction efficiency if the filled concrete in a steel box column could be eliminated. To determine the seismic behaviours of this connection economically, this study developed a complex nonlinear finite element model (FEM) using the ABAQUS software. After verifying the FEM, four different representative FEMs of joint configurations without concrete filling in the column, including a 2D interior, a 3D interior, a 3D exterior, and a 3D corner joint, were established and loaded with unidirectional and bidirectional cyclic loads. The hysteresis behaviour under different axial load levels in the column was analysed. In addition, to compare the seismic performance of different joint forms more intuitively, the vertical load–displacement relationships at beam ends were equivalently expressed as the storey shear force versus the storey drift of one column according to the energy equivalence principle. The results show that various ConXL connection joint configurations without concrete filling in the column show beam hinge mechanism failure mode when the axial load level in the column is not too high (~ 0.4). However, the failure mode becomes beam–column hinge hybrid failure mechanism or even column hinge mechanism with an increase in the axial load level. The seismic behaviours are acceptable according to AISC 341, and the panel zone does not show yielding, making it suitable for application as a beam–column connection in steel moment frame structures.