The Effect of Reduced Section of RBS Connection on the Intact Section

One of the connections which is designed based on the concept of weakening the beam is Reduced Beam Section (RBS) connection. The 1994 Northridge earthquake caused widespread damage to moment-resisting frames. Various brittle fractures were found in beam-to-column welded moment connections. So far numerous efforts have been made to find a better connection configuration to improve the behavior of the post-Northridge moment connections. The improvements are mainly based
on the connection reinforcement or the weakening of the beam section. These methods are intended to force the plastic hinge to form away from the column face and consequently increasing the connection ductility. The reduced beam section (RBS) protects a welded SMRF connection detail by forcing the plastic hinge in a beam to form away from the column face. Traditionally, welded SMRF connection design requires using a strong column-weak beam combination, which means that any instability in the frame would result from plastic hinging in the beams rather than the columns. With maximum moments occurring at the beam-column interface in moment frames under lateral loading, the plastic hinges will form at the column face, placing high strain demand on the weldment. An elastic-plastic fiber model is presented herein to analyze the column tip load vs. RBS contribution to total story drift curve. Isolation of RBS material behavior requires that the rest of the material in the frame is treated as rigid forcing all of the deformation into the RBS. Considering the advantages of RBS moment connections and lack of knowledge of the performance of this connection with respect to Indian profiles led to a study on this topic. The objective of this study was to investigate experimentally the cyclic behaviour of welded moment connections with and without RBS. The idea of weakening the beam near the end of the beam is achieved by trimming some parts of the beam flange near the column face forcing the formation of plastic hinge in this region. The RBS area acts as a fuse. In this study, cyclic performance of the Reduced Beam Section connection is studied in a numerical environment by using ABAQUS software. The investigated connection is a single-sided beam-to-column assembly. The cyclic load is applied at the tip of the beam. Length of the beam is a half of determined span in a designed building. Pinned boundary condition is applied at the top and bottom of the column and out of plane displacement of the beam is restricted. No weld fracture was observed in RBS connection while there was a crack observed near beam bottom flange weld for connection without RBS. A reduction in material and labour cost is possible due to elimination of continuity/doubler plates for RBS moment connection. The loading protocol proposed by AISC is used for cyclic loading. In parametric study of this connection, the effects of changing dimensions of reduced area are investigated. The results reveal that the moment capacity of RBS connection is less than the moment capacity of a corresponding intact section connection but no plastic hinge is formed in intact section connection.