Seismic performance of bidirectional bolted drilled cut RBS-CFT connections under cyclic loads

Abstract

Welded connections were widely used in different regions of the world for ease of fabrication and good performance under gravity load. However, Northridge (1994) and Kobe (1995) earthquakes demonstrated that seismic performance of welded connections has been inferior as compared to that of bolted connections. Reduced beam section (RBS) has been one of the effective methods to enhance seismic performance in terms of energy dissipation capacity and ductility. Drilled-cut RBS-CFT connections have been gaining acceptance for enhancing overall seismic performance of steel moment resisting frames. However, no comparative study has been reported in the literature on RBS-CFT connection with bidirectional bolts for evaluation of their seismic performance. In view of the above, experimental study has been carried out for evaluation of seismic performance of two variants of RBS-CFT connections with constant drilled cut (CD-cut) and varied drilled cut (VD-cut) RBS. Both the drilled cut RBS-CFT connections are found to be semi-rigid in nature and exhibited stable hysteretic behavior. Test results showed that the cumulative energy dissipation capacity in the VD-cut connections is marginally higher than CD-cut connection. VD-cut RBS-CFT connections effectively reduced the lateral-torsional deformation. The load-carrying capacity and stiffness degradation ratio of VD-cut RBS-CFT connection is higher than CD-cut RBS-CFT connection. Damping of the both connections are nearly of similar order. Recorded strain data of both connections showed that plastic hinge confined only on drilled zone of the beam. Further, a detailed numerical simulation of force-deformation envelope curve of RBS-CFT connections was carried out using ABAQUS software. Simulated force-deformation envelope curves are found to be in close agreement with those obtained from experimental investigation. Both connections meet the seismic requirements of the AISC specified for composite special moment-resisting frames (SMRFs) by achieving rotational capacity of 0.04 radians without any damage in the joint panel region.