Response modification factor of eccentrically braced frames with reduced beam section

Abstract

Eccentrically braced frames are one of the most proper lateral resisting systems in seismic areas. The link beam in an eccentrically braced frame acts like a structural fuse, which is able to sustain large plastic shear or flexural deformations. Therefore, other structural members such as beams and columns are expected to remain elastic during a severe seismic ground motion. The reduced beam section has recently been proposed for moment resisting frames, which results in the concentration of the plastic deformations at the ends of the beams and in a place far from the connection. In this paper, reduced beam sections are implemented in an eccentrically braced frame (Dual system) at the ends of link beams as well as other beams placed inside the moment resisting frame. Finite element analyses in ABAQUS software are conducted in order to evaluate and compare the seismic response of the eccentrically braced frames with reduced beam sections and without them. For this purpose, 4, 8, and 12 story braced frames designed according to Iranian national building codes are considered. Pushover analysis and also nonlinear time history analysis are carried out. The results show that the braced frames including reduced beam sections at the ends of the link beam and other beams, possess higher ductility and response modification factor. In addition, the results show that during time history analyses, the systems with reduced beam sections experience higher inter-story drift demands in comparison to the system without reduced beam section.

Keywords

• eccentrically braced frame
• reduced beam section
• response modification factor
• pushover analysis
• time history analysis