Reduced Beam Section (RBS) moment resisting connections are among the most economical and practical rigid steel connections developed in the aftermath of the 1994 Northridge and the 1995 Kobe earthquakes. Although the RBS connection effectiveness was widely investigated using US design and construction practices, only limited data exist from European research. Recommendations of RBS applications in steel frames were prescribed in EC8, Part3. However the reliability of these recommendations is under consideration due to above mentioned poor existing data. This paper examines numerous different contours of radius cut-out (Group A) and provides recommendations for the design and detailing of radius cut Reduced Beam Section (RBS) moment connections. Furthermore, it examines and compares different beam cross sections of European steel profiles (Group B) while the sizing of the RBS cut is kept at a constant ratio. Analytical approach was conducted investigating the adopted by EC8, Part 3 key parameters for the design. The main objective of the applied RBS geometry is to protect the connection and its components (endplate, column flange, bolts, welds) from either plastification or failure. Although the computational cost for optimization with ABAQUS is very large, the results of this study ensures on one hand that the performances of the structural parts can be effectively improved by shape optimization and an the other hand that adjustment in the geometry of the radius cut is needed for safe application to European profiles.
Widespread damage to steel moment frame structures during the 1994 Northridge and 1995 Cobe earthquakes led researchers to develop alternative connection designs to the prescriptive pre-Northridge moment connection. Two key concepts have been developed to provide highly ductile response and reliable performance; strengthening the connection and/or weakening the beam framing to the column, in order to avoid damages of the respective column. The weakening of specific sections of the beam in order to change them into reliable energy dissipative zones, in case of an earthquake, is an idea which was developed in principle in the late '80s by Andre Plumier. There has been previous testing on the RBS moment connections which heralds the effectiveness of the new approach in the post-Northridge design era. The reduced beam section (RBS), allows controlled yielding of the beam by moving the plastic hinge region at the beam -in a short distance from the column's face-protecting the connection from any type of failure.Various shapes cutouts are possible (constant, tapered or radius cut) to reduce the cross sectional area. Extensive experimental and analytical projects have been conducted demonstrating that the curved RBS behaves with the highest rotational capacity. Recommendations for the design and detailing of the RBS member were prescribed in FE-MA 350 and FEMA 351, regarding the location and reduction rate of RBS, based on the local performance of tested beam to column assemblies. In Europe, also, following the concept of the above mentioned recommendations, in EC8, Part 3, design of such type of connections is presented.xvi the need for further investigation -concerning the effectiveness of the RBS use in this type of connections and for the possible readjustment of the geometrical characteristics of the RBS -is imperative in order to be safely applied to the European profiles.
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