Post tensioned tendons for seismic retrofitting of weak bolted T-stub connections

Abstract

Current design philosophy for conventional steel moment resisting frames (MRFs) in high seismic regions is that the frames should not collapse for major earthquakes. However, significant structural damage and residual drift due to inelastic deformations in beams and columns may cause loss of building occupancy or operation after major earthquakes. On the other hand, Selecting the optimum technique for rehabilitation of existing structures with weak connections has been a challenge for engineers in the recent years. In this study, the authors proposed using post-tensioned tendons for rehabilitation of bolted Tstub connections with weak bolts or weak T-stub flange as well as a technique for changing pinned connections to moment connections. Six corner connection specimens are made and tested under SAC cyclic loading protocol. The results of this study show that this rehabilitation technique not only modifies the cyclic behavior of weak rigid connections and changes simple bolted connections into moment connections, but also it improves the behavior of the rehabilitated connections in a way that their behavior is more desirable than that of the reference rigid connection designed according to AISC. For example, flexural capacity and rotational stiffness of the retrofitted connections are higher than those of the reference connection by 18 and 26% in average respectively. Besides, rehabilitation using post tensioned tendons add self-centering ability to the retrofitted connection that has a major role in preventing permanent deformations in frame and thus, the possibility of using frictional dampers in self-centering frames for increasing the energy absorption capacity is provided. This rehabilitation technique in bolted connection with weak T-stub flange has better cyclic behavior compared to that of a connection with weak bolts, since the T-stub participates in energy absorption and higher energy absorption is reached.