Seismic performance of pre-northridge welded steel moment connections to built-up box columns

Results of experimental and analytical investigations of the seismic response of fully restrained steel moment connections between deep W-shape beams and deep and square built-up box columns are presented. Prototype beam-column connections were selected from the steel moment-resisting frames in a building built before the 1994 Northridge earthquake. Two full-size, single sided, pre-Northridge box column connection assemblage specimens were fabricated using the prototype connection data. Pretest analyses showed that the responses of box column connections can be substantially different from W-shape column connections. Both specimens were tested using a standard connection prequalification test protocol and each failed by brittle fracture in the complete joint penetration (CJP) welds of the beam flanges at connection drift angles less than 0.8% rad. The pre-Northridge beam flange CJP welds are likely to fail in a brittle manner regardless of the type of column cross section. ABAQUS finite-element models of the specimens were validated using the test results. The locations of the cracks in the beam flange CJP welds coincide with the region of high axial stresses, which varies depending on the column type, presence of continuity plates, and thickness of box-column plates.