Retrofit of Typical Rigid Steel Connection Using Reduced Beam Flange Section

The moment connections sustained by many steel buildings were damaged during the recent earthquakes due to brittle fractures in the special moment resistant frames. Previous studies showed that although the top beam flange resisted due to the interaction of concrete slab, many damages are created because of weld cracking between the bottom beam flange and the column flange. Different methods of retrofit and rehabilitation could be used to prevent weld cracking and brittle fracture of the joints. The reduction of the bottom flanges of steel beams near the beam-column joints in the special moment resistant frames is currently an acceptable alteration of a connection because the top flange is located in the concrete slab and removing of concrete slab has financial and technical problems. RBS connection is one of the different kinds of Post-Northridge connections in which by cutting some parts of the flange near the end of the beam (where the possibility of making plastic hinges is high), the plastic hinge moves by the side of the column into the area within the beam. By using this method, the connection is altered from the special moment frame into a more ductile connection that has more ability to endure in plastic rotation, and generally ductility increases. The ductility of the panel zone is one of the parameters, which undoubtedly affects the manner of the yield of beams with RBS connection. Our findings in this work showed that new method causes the beam plastic rotation to increase by 30%. In addition, the applied force at the panel zone (according to the capacity of panel zone) is decreased. When compared to the frames without cuts, these reductions result in a 52% decrease in the plastic rotation of the panel zone, we also investigated the amount of dissipated energy by beams in the conditions before and after retrofitting. ANSYS software was used to study and analyze the non-linear behavior in the area of connections.