Analytical Study on All Types of Reduce Beam Section Moment Connections Effecting Cyclic Behavior

Abstract

The recent earthquake have been shown steel moment frame (SMF) with weld connections are so brittle. According to researches, the more damage were due to cracking of the weld between the beam flange and the column face and induced concentrated stresses in this area. A useful approach to reduce the stress concentration at the panel zone is using of reduce beam section (RBS). Given the enormous impact of seismic behavior and ductility of the panel zone, RBS moves plastic hinge formation at appropriate distance from column face. In this study, a moment connection with different shape of reducing beam flange and web have been modeled using ABAQUS computer program and compared with each other during cyclic behavior. This paper is to present the results of numerical modeling on four subassemblies RBS moment connections. The beam flanges and web reduced by two method that were radial cutting and circular cutting. The circles of one of models were the same and one of them increase gradually. The main objectives are: (1) to comparison between all type of RBS connection on ductility; (2) to study the effect of all type of reduce beam connection on the concentration stress and strain in different zones (3) to study the effect of all type of reduce beam connection on the concentration equivalent plastic strain at integration point (PEEQ) in different zones ; (4) to obtain the influence of various type of reduce flange section on dissipated energy by the whole model; (5) to consider the buckling behavior of the exterior models; (6) to obtain connections secant stiffness and classification them. This study shown that RBS moment connection translate plastic hinge and concentrated of stress from connection to the reduce area. Also RBS connection with Variable radius Hole (RBS-VH) increase stiffness of panel zone, dissipated energy by whole model and ductility of connection. The result of this study show that all models have reached to 0.04 radians rotation, and the strength of connection at 0.04 radians rotation, is more than 80 percent of the beam plastic moment capacity, (0.8Mp). Consequently this connection satisfies the criteria of AISC Seismic Provisions (2005) for special moment frame systems. According to AISC Specifications for Structural Steel Buildings (2005), if KL/ EI > 20, the connection can be considered as fully restrained. Where L and EI are length and bending rigidity of the beam respectively. Values of secant stiffness and KL/EI are presented in the result for all models. As the result shown, all values of KL/EI for RBS connection are greater than 20, therefore according AISC Seismic Provisions, this connection can be classified as a fully restrained (FR) connection. As the result shown, cut the flange area using circles that increase gradually provide beam and connection behavior against buckling.