Optimization of Reduced Beam Sections (RBS) for Ductile Detailing of Seismic Joint Connections Using Finite Element Analysis (FEA)

Abstract

Steel structures used as Special Moment Resisting Frames (SMRF) designed to resist lateral loads (due to wind and seismic) are expected to undergo large inelastic deformations, hence the ductility requirements are explicitly stated in almost all standards. In any given frame, inelastic deformations should occur in the horizontal elements (e.g. beams) in the form of plastic hinges. Most structural analysis can be performed assuming the beam-column joint (nodes) as a fixed (rigid) connection, however, this may mean that hinging may occur at the connection and thus possibly affect the column through the flange or web connection. In order to ensure a ductile system can be achieved, special detailing requirements are necessary. Among the available methods require the use of Reduced Beam Sections (RBS) adjacent to the beam-column connection to warrant the strong-column/weak-beam design philosophy. The main objective of this paper is to optimize the geometry of the RBS using Finite Element Analysis (FEA) in conjunction with the available standards e.g. BS EN 1998-3 and ANSI/AISC 358-16. While standard codes of practice provide the range of values that can be used in determining the geometry of the RBS, it would be beneficial for a designer to come up with basic rules-of-thumb that can be applied in actual design calculations.

Keywords

• special moment resisting frames (smrf)
• plastic hinge
• reduced beam section (rbs)
• ductile detailing