Tension bolt behavior in moment connections for seismic applications




Ulloa Barbaran, Fernando Valentin

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Recent seismic events such as the Northridge earthquake have left behind, along with destruction serious doubts about the performance of the welded moment connection, until now the most popular and reliable steel beam-column connection. A careful study of the structures damaged by these earthquakes, has established that welded connections mainly failed due to fracture along the full penetration groove weld. This rather unexpected behavior of this type of connection has prompted additional research on welded connections and research on other type of connections, i.e., bolted connections. The former has led to some recommendations aimed mainly at strengthening of the connection by making use of additional stiffeners and new welding techniques. All of this has resulted in an increase of the overall cost of this type of connection, in such a way that the previously more expensive bolted connection has become a viable alternative to the traditional welded connection. All bolted beam-column connections are controlled by the behavior of the structural members connecting the beam flange to the column flange, i.e. Tees, angles. High strength bolts are used as the connectors. These Tees generally are designed as hanger-type connections. While extensive work on hanger-type connections subjected to monotonic loading has been reported, very limited work has been done on these type of connections subjected to cyclic loading. A set of tests involving five full scale specimens, all bolted beam-column connections, were performed at the University of Texas at Austin. The goal of these tests was to study the behavior of this type of beam-column connection when subjected to cyclic loading and devising seismic design guidelines and recommendations for a proper design of this type of connection