WUF-W connection performance to box column subjected to uniaxial and biaxial loading

•WUF-W connection to the box column was prequalified for all the test specimens.•The value of Cpr in the WUF-W connection to the box column should be taken as 1.3.•The connection to the box column under biaxial loading achieved AISC requirements.•To prevent formation of the flexible panel zone, SCWB ratio should be more than 1.3.•Thick continuity plates may not be appropriate in large beams to the box column.

The prequalified connections presented in AISC are limited to the connections of the I beam to wide flange columns. It is necessary to investigate the seismic performance of the prequalified connections to the box column, which has a very low strength and stiffness panel zone in contrast with the wide flange column. In this study, the seismic behavior of the WUF-W (welded unreinforced flange) connection to the box column was investigated through full-scale cyclic loading tests. The experimental results revealed that this type of connection to the box column can satisfy the prequalified criteria of the special moment frame. Moreover, the main advantage of using box column is its high biaxial bending strength. Therefore, as part of the analytical study, the connection subjected to biaxial loading for a series of parameters was investigated. The analytical investigation showed that in order to achieve the desired performance under biaxial loading, the panel zone must provide the strong column/weak beam ratio of more than what is suggested by AISC. Furthermore, the analytical study revealed that for the box column under biaxial loading, the inner diaphragm may not be suitable because of the potential for the weld to fracture.