Seismic Behavior of Steel Moment Frame Connections with Repairs in the Plastic Hinge Region

Abstract

Steel moment frames develop large drift capacity and dissipate seismic energy through inelastic deformation in the plastic hinge region near the beam-to-column connection. To discourage fracture in this region, known as the protected zone, attachments are limited to arc spot welds and power-actuated fasteners for decking attachment. Other attachments or defects like shear studs, bolts, holes, gouges, and notches must be removed and repaired by grinding or by a combination of grinding and welding. These requirements are given in the AWS D1.8/D1.8M seismic welding code, but there have been no full-scale connection tests with these repairs in the plastic hinge region. For that reason, this research evaluated the performance of moment connections with repairs by testing six full-scale reduced beam section moment connections with W24×62 and W36×150 beams. The following defects and repairs were included in the beam protected zone: 3.17-mm (1/8-in.)-deep notches repaired by grinding, 6.35-mm (1/4-in.)-deep notches repaired by welding, and sharp 6.35-mm and 9.53-mm (1/4-in. and 3/8-in.) semicircular notches. The specimens were tested in an exterior column configuration and subjected to the cyclic special moment frame qualification displacement protocol given in ANSI/AISC 341. All four specimens with repairs maintained substantial flexural strength through cycles of 5% story drift ratio and satisfied special moment frame qualification criteria. It is concluded that the AWS D1.8/D1.8M repairs resulted in sufficient ductility for use in special moment frames within the range of parameters tested. The two specimens with unrepaired sharp notches experienced fractures propagating from the notches, causing substantial loss of flexural strength during cycles of 3% or 4% story drift ratio.