Cyclic performance of extended end-plate connections equipped with shape memory alloy bolts

Shape memory alloys (SMAs) are nowadays promising candidates for seismic engineering applications because of their ability to undergo reversible deformations and to dissipate energy when subjected to cyclic loading. This paper presents an experimental study of the cyclic performance of extended end-plate connections connected using SMA bolts instead of normal high strength bolts in the connections. The basic concept is to concentrate the earthquake-induced deformation into the connection, such that a 'superelastic' hinge can be formed via the elongation of the SMA bolts. Eight full-scale tests were conducted including seven extended end-plate connections with SMA bolts and one conventional extended end-plate connection with normal high strength bolts. The SMA connection specimens were shown to have excellent recentring abilities and moderate energy dissipation capability with an equivalent viscous damping up to 17.5%. The stiffness and strength of these connections mainly fell into the semi-rigid and partial-strength categories, respectively. The ductility, which was governed by SMA bolt rupture, was found to be dependent on the net threaded-to-shank area ratio of the bolts, where a lower ratio led to earlier bolt fracture over the net threaded cross-section. On the other hand, the conventional extended end-plate connection with High Strength bolts was shown to have good energy dissipation capability and ductility but with considerable permanent deformation. To enable a further understanding of the SMA connections, preliminary numerical models were established and validated by the test results. Based on the results of the tests and the numerical investigations, preliminary design considerations for such connections are given.