Hinge joint performance in hollow-core slab bridges transversely strengthened with local near-surface mounted iron-based shape memory alloy (Fe-SMA) bars

Hinge joints provide key lateral connections within hollow-core slab (HCS) bridges, providing load transfer between adjacent beams. However, hinge joints are prone to cracking, which is a common problem in HCS bridges. Therefore, the present study proposes a novel technique for transverse strengthening of hinge joints by utilizing locally near-surface mounted (NSM) Fe-SMA bars, based on the self-prestressing mechanism of iron-based shape memory alloys (Fe-SMAs). To verify the feasibility of the strengthening technique, 13 slab beam-hinge joint specimens are prepared and loaded under a flexural-shear load in combination with digital image correlation (DIC) tests. The test series encompasses two quantities of Fe-SMA bars (one and two), two activation lengths (100 mm and 200 mm), and three activation temperatures (non-activated, 200 ℃, and 400 ℃). The generated self-prestress level for the strengthening technique is investigated based on experimental data. The results indicate that the strengthening technique can effectively enhance the lateral connection of adjacent HCS beams and the mechanical behavior of hinge joints. Increasing the quantity of Fe-SMA bars and the activation temperature can significantly increase the cracking load, crack penetration load, and ultimate load of hinge joints. Activation lengths of 100 mm and 200 mm have a limited effect on strengthening. At 200 ℃ and 400 ℃ activation temperatures, the effective prestresses based on analysis are 277 ± 19 MPa and 411 ± 21 MPa, respectively.