REDUCED BEAM WEB (RBW) CONNECTIONS WITH CIRCULAR OPENINGS

Abstract

From 1988 to 1994, the Uniform Building Code (UBC) prescribed a beam-to-column connection to be used in steel special moment frames. This connection type is known as Pre-Northridge connection. Numerous tests have been done until 1994 to investigate the ductility level of the Pre-Northridge connections. Most of these tests were successful, with a number of specimens sustaining total rotation larger than 0.04 rad. Despite of the design expectations and the successful tests, the 1994 Northridge earthquake showed that the level of ductility of pre-Northridge connections is lower than the required levels. Research results showed that higher ductility can be achieved by using smooth weld access holes, high fracture toughness weld metal E70-TGK2 and removing the bottom beam flange backing bar. This type of modified pre-Northridge connections are known as post-Northridge connections. However, these modifications may not lead to achieving minimum required ductility levels. To improve the ductility of post-Northridge connections, researchers started to change the connection configuration by keeping the previously mentioned modifications. One of the such modified connections is reduced beam web (RBW) connection. In RBW connection the beam web is penetrated by a number of circular voids. The size and spacing between the voids are designed as such to cause the shear yielding of the beam web along the beam span and to keep the connection in elastic region. Experimental tests of RBW connections indicated that these connections could achieve adequate strength and ductility. This chapter aimed to use the above mentioned design criterion to investigate whether connections of beams deeper than those previously tested could also achieve adequate strength and ductility. In addition, the effect of moment yielding and shear-moment yielding criterions on the behaviour of RBW connection were also investigated. Hence, using finite element method, three pre-tested post-Northridge connections with deep beams of different depths were modeled. Results showed that web shear yielding criterion can lead to higher connection ductility. Furthermore, multiple voids of same size at the beam web area could only increase the total rotation of the shallowest beam specimen (600 mm beam depth) to the minimum required ductility. Therefore, a void arrangement of different void sizes was proposed for deep beams in terms of the beam depth.