Comparison of Strength, Stiffness and Ductility of Reduced Beam Section Subjected to Lateral Loads Only and Combined Gravity And Lateral Loads

Lateral loads from Northridge Earthquake in 1994 caused brittle fractures at column-beam connections in rigid frame structures which hitherto were thought to have high ductility to resist such brittle fractures. These brittle fractures were caused by the moment frame connections’ inability to undergo inelastic deformation which eventually resulted in several structural damages. Reduced beam section (RBS) connection was among one of the solutions proposed by researchers following the Northridge Earthquake. In RBS connections, part of the beam flanges or web at a distance from the face of the column is selectively cut off to reduce its capacity in order to induce plastic hinge away from the beam-column interface. Reducing the beam section, weakens the beam and allows the groove welds and the panel zone to have a higher strength compared to the beam, thereby achieving stronger column-weaker beam design which have a better seismic performance. RBS must provide adequate combination of stiffness, strength and ductility in order to ensure acceptable seismic performance. The scope of this study is to compare strength, ductility and stiffness of reduced beam section under lateral loads only and combined gravity and lateral loads. Four finite element models were created with all conditions kept constant except loading conditions on the frames. Results from this study indicates that all models have almost the same stiffness with the models under combined gravity and lateral loads having higher ductility and ultimate strength