Cyclic Behavior of Bolted Stiffened End-Plate Moment Connections for Different Bolt Pretensioning Levels: An Experimental Study

Bolted stiffened end-plate moment connections are one of the most usable connections used as a prequalified connection in special steel moment frames. According to the AISC design code, this connection can be considered one of the most important parts of moment resisting frames with enough bolt pretension levels. In this paper, using three full-scale bolted stiffened end-plate moment connections designed according to AISC, the effects of bolt pretension levels have been examined experimentally under SAC cyclic-loading protocol. Bolt pretension level has been defined as α coefficient to show pretensioning level in three specimens. The bolts of the first specimen are not pretensioned, called snug-tightened bolts, and are reference connections. The bolt pretension level of the second and third specimen is created in accordance with the AISC design code and more to Fu of bolts, called pretensioned and fully pretensioned, respectively. The bolt’s moment capacity, total energy absorption, initial rotational stiffness, and ductility of connection as well as stress and strain variation have been investigated. According to the results, increase in bolt pretension level would significantly improve the cyclic behavior of connections. Furthermore, an increase in bolt pretension led to the initiation of the inelastic deformation from a smaller rotation, and the ductility of the connection improved. In addition, the rate of growth in moment capacity and energy absorption in the pretensioned specimen was 8% and 9% compared with fully pretensioned, respectively. Note that the connection with bolt pretension level by design regulations in comparison with the reference connection can be considered as a connection of a special moment resisting frames where bolt pretension level higher than the value mentioned in the design code is better but not needed.