Long-term behavior of stud connections in steel-alkali activated UHPC composite structures

In this paper, a long-term experimental program consisting of twenty push-out specimens is conducted to investigate the long-term behavior of the stud connections in steel-Alkali-activated ultra-high-performance concrete (AAUHPC) composite structures, considering the effects of steel fiber content, water-to-binder (W/B) ratio, loading level, loading age, and stud diameter. The effects of these factors on the total slip, instantaneous slip, creep-induced slip, and shrinkage-induced slip of the stud connections are studied. The long-term tests are performed over a period of 180 days, during which eleven of the test specimens are employed for long-term push-out tests under sustained load, while nine specimens are used for shrinkage tests. The obtained results illustrate that decreasing the W/B ratio is an efficient way to alleviate the long-term slip of the stud connection, and the adoption of steel fiber with a content of 2 % is recommended. Compared to the instantaneous slip, the effect of loading level is more pronounced on the long-term slip. Additionally, the long-term slip of the stud connections is primarily induced by creep, while the effect of shrinkage is relatively small. Furthermore, three models, including the generalized Kelvin model, Burgers model, and logarithmic model, are deployed for capturing the creep compliance of the stud connection, and the comparisons demonstrate the superiority of the Burgers model. © 2025 Elsevier Ltd.