Hysteretic behavior of precast segmental bridge piers with superelastic shape memory alloy bars

Precast segmental bridge constructions are currently the subject of intensive research in several countries around the world: the USA and Taiwan, amongst others. Especially in the case of post-tensioned (PT) segmental bridge piers, several methods have been suggested to increase the energy dissipation capacity, such as the use of fiber reinforcement, exterior yielding devices at the base segment, and mild steel bars. As a new alternative, in this paper, the use of superelastic shape memory alloy (SMA) bars is suggested in order to improve the hysteretic performance including the energy dissipation capacity of the bridge columns. The use of SMA bars ensures a self-centering capacity to the PT column system. The segments are connected strongly to each other by using rigid links which prevent potential joint openings. Opening at the bottom of the base segment is allowed, leading to the same behavior as that of a single rocking column which is similar to a double-hinged gravity column. Such a column is modeled with a moment-curvature relationship and spread nonlinearity (plasticity) model. Unbonded PT tendons are modeled by a linear spring and the uniaxial behavior of the superelastic SAM bars is modeled with a combination of four springs, namely a post-yielding spring, a hysteretic spring, a slip-lock spring and a gap-closing spring. The SMA model developed provides a good cyclic performance. Considering a segmental bridge pier with 7.5 slenderness, a quasi-static cyclic analysis is carried out to investigate the hysteretic response. The results show that stable energy dissipation, self-centering, and high ductile behavior are achieved with the PT column system.