Seismic analysis of eight-bolt unstiffened end plate moment connections

The eight-bolt stiffened extended end plate moment (8ES) connection is preapproved for use in intermediate and special moment frames according to ANSI/AISC 358. Simulated seismic testing indicates that 8ES connections generally perform well, exhibiting ductile failure modes. Despite this, many studies have found that the beam flange near the stiffener toe is prone to fracture due to the high stress concentration in that area. Recently, a solution to this problem was proposed - an unstiffened eight-bolt extended end plate connection. This removes the stiffener and arranges bolts in an octagonal pattern to eliminate stress concentration and ensure equal force distribution. When using the proposed unstiffened connection with deep wide flange beams (e.g., W-sections of 900 mm nominal depth), detailed finite element analyses performed in this study showed that high strain demands at the beam flange to end plate CJP welds can develop despite improvements. Hence, two additional seismic performance enhancing techniques are analytically evaluated for unreinforced eight-bolt extended end plate connections. The first technique uses heat treatment of specified beam flange regions and reinforcing specified beam web regions. The heat treatment relocates the plastic hinge and thereby lower flange weld strain demands, whereas web reinforcement delays the onset and slows the rate of connection strength degradation. The second technique uses a heavy extended shear tab to relocate the plastic hinge away from flange weld and slightly delays the onset of strength degradation. Systematic analysis results are developed and presented to demonstrate the enhanced seismic performance of the modified EEP connections and to plan future experimentations and design development.