Simulation-Based Fracture Assessment of Seismic Moment Frame Connections with Box Columns

Welded connections between beams and built-up box columns in steel moment frames require the attachment of continuity plates to the inside of the column using complete-joint-penetration (CJP) groove welds. Electroslag welding (ESW) is often used to weld at least one of the four sides of each continuity plate to the inside of the box column. These welds are susceptible to fracture due to decreased material toughness and installation of containment plates that create a notch condition. Finite-element simulations are presented to examine the effect of design and detailing parameters on the fracture of these connections, as assessed through conventional fracture mechanics as well as continuum damage mechanics. The results indicate that improved bevel details in the containment plate and reduced beam section (RBS) connections strongly mitigate fracture demands, whereas both eccentricity in the weld with respect to the continuity plate and unequal beam and column flange widths exacerbate demands. The beam and column size, as well as beam web weld access hole details, have only a modest effect on the demands. Simulations are also conducted to examine column-wall thickness limits beyond which continuity plates may not be required. These suggest that limits similar to those specified for wide-flanged columns may not provide adequate performance. Limitations of the study are presented, along with directions for future work.