Finite element analysis of moment resisting steel connections based on DBYBHY-2007

Moment resisting ductile steel frame systems are widely used in seismic zones, due to their high ductulity capacity. However, investigations conducted after the 1994 Northridge Earthquake showed that some brittle fracture occurs on weldings of connections and structural steel close to weldings. The SAC Steel Project funded by the FEMA (Federal Emergency Management Agency) has started intensive test program to dispose the causes of brittle fractures, provide solutions and improve connections performance. Recommended connection types have been presented in report entitled FEMA-350. Six connections proposed FEMA-350 including three bolted and three welded ones are even specified in Specification for Buildings to be Built in Seismic Zones (DBYBHY-2007). Bolted connections are entitled as bolted unstiffened end plate connection, bolted stiffened end plate connection and bolted flange plate connection, while welded connections are entitled as welded unreinforced flange – welded web connection, welded flange plate connection and reduced beam section connection. This thesis aims to assess the performance of moment resisting steel column – beam connections based on DBYBHY-2007 under monotonic and cyclic loading with finite element analysis. Before analyze mentioned connections, to evaluate the adequacy of numerical analysis to be conducted in this study, experimental and numerical results of two examples from the literature are considered and compared with the results of this study. It is obtained that the results of this study and the experimental and numerical results in the literature are in good agreement with each other. After verification of finite element modeling, modeling process of connections based of DBYBHY-2007 and results of analyses are explained. Material and geometry nonlinearities are considered. Contacts between connection parts such as bolt, column and beam are considered as linear and nonlinear. After analyses, first, the mentioned bolted and welded connections are compared between themselves, then one bolted and one welded connections which have better performance than other connections are compared with each other. The results reveal that bolted flange plate connection model shows an invalid failure mode. It is showed that, bolted stiffened end plate connection from bolted ones and welded flange plate connection from welded ones are more reliable than other connections in terms of plastic hinge location, moment capacity and stiffness.