www.springer.com/journal/13296 International Journal of Steel Structures 15(4): 827-834 (2015) DOI 10.1007/s13296-015-1205-7 ISSN 1598-2351 (Print) ISSN 2093-6311 (Online) The Effect of Stiffener on Behavior of Reduced Beam Section Connections in Steel Moment-Resisting Frames M. Tahamouli Roudsari 1, * , F. Abdollahi 2 , H. Salimi 2 , S. Azizi 2 , and A. R. Khosravi 3 1 Assistant Professor, Department of Civil Engineering, Kermanshah Branch, Islamic Azad University, Kermanshah, Iran 2 M Sc. Student, Department of Civil Engineering, Kermanshah Branch, Islamic Azad University, Kermanshah, Iran 3 M Sc. Student, Department of Civil Engineering, Dezful Branch, Islamic Azad University, Dezful, Iran Abstract Reduced Beam Section (RBS) connections are a new type of connection which have been used in steel moment-resisting frames since the 1994 Northridge earthquake. This study is primarily aimed at analyzing the effects of suitable web stiffeners on preventing the deterioration effect of the hysteresis curve for RBS connections. Results of more than 183 nonlinear finite element analyses on different IPE sections with radius cut, straight cut, and drilled-flange RBS connection showed that different web stiffeners considerably contribute to the enhancement of seismic performance of RBS connections. In this research, the effects of factors such as the geometry and the number of the stiffeners, the distance between the stiffener and column side, and the length and thickness of the stiffener on the seismic performance of RBS connections were also studied. Keywords: stiffener, RBS connections, steel moment-resisting frame, lateral torsional buckling, web buckling 1. Introduction Moment-resisting frame connections are designed to resist shear force and bending moment, create plastic hinges, and dissipate the energy of earthquakes in cyclic motions. Before the 1994 Northridge earthquake, steel moment-resisting frames specifically designed for seismic zones were commonly used in the United States. By then, using the beam-column connection through groove welding was highly prevalent as they were thought of as the type of connection that can bear high degrees of plastic deformation. However, in the Northridge and Kobe earthquakes, researchers observed the spread of brittle cracks and fractures in the connections (Chi et al., 1998; Righiniotis and Imam, 2004). Therefore, it was perceived that the assumption was flawed and hence the trust in most typical connections incorporated into moment- resisting frames was lost considerably. In order to enhance the performance of moment- resisting frames in powerful earthquakes, the following two methods were proposed: reinforcing the connections and weakening the beam in the vicinity of the connections. The second method leads to the formation of plastic joints outside of the connection and a decrease in the demand for force and moment at the junction. This method led to the development of a new type of connection known as the Reduced Beam Section (RBS) connection. Notwithstanding their major advantages, there are also disadvantages to RBS connections such as increased concentration of stress on the site of reduced beam section, slight structural lateral strength and stiffness decrease, and an increased possibility of local buckling on the web and also a higher chance of lateral torsional buckling. Recently, numerous studies have addressed RBS connections. Some of these studies are referred to in the following. In 2009 Ohsaki et al. studied the effect of cutting shape on the hysteresis behavior of the reduced section. They calculated the optimal shape of radius cut based on the maximum possible amount of energy dissipation in a cantilever beam. Using the ABAQUS software, they drew a comparison between the results of calculations and experimental results. Pachoumis et al. (2009, 2010), conducted studies on RBS connections and their hysteresis behavior. They confirmed appropriate behavior of these connections based on the results of numerical and experimental tests. They also suggested that the criteria presented in AISC was unsuitable for the dimensions and distances of cuts in RBS connections that have been made of European built sections and called for modifying the Received December 16, 2014; accepted May 28, 2015; published online December 31, 2015 © KSSC and Springer 2015 *Corresponding author Tel: +989183591051, Fax: +988337237470 E-mail: tahamouli@iauksh.ac.ir