This present study investigates the failure mechanisms and damage evolution at the steel-UHPC interface through static push -out tests and active sensing monitoring on 15 steel-UHPC specimens. To address the ductility issue of embedded studs in UHPC as specified by Eurocode 4 to be at least 6 mm, the selected parameters particularly include large -diameter studs (>= 25 mm), high -strength studs, and bolted connectors, which less frequently involved in current research. The test results indicate that large -diameter studs and bolted connectors can enhance the ductility of the steel-UHPC specimens. However, the use of high -strength studs further reduced the ductility of the specimens due to welding quality issues. Furthermore, to explore the evolution of damage at the steel-UHPC interface, the Piezoelectric Transducer (PZT)-based active sensing system was employed to continuously monitor the development of slip damage at the steel-UHPC interface during the static push -out tests and then evaluate the specimen's damage under different loading conditions. By analyzing the wave response of the piezoelectric sensor, the results reveal a strong correlation between the damage index, obtained through wavelet packet analysis, and the progression of interface slip. This correlation enables precise identification of critical damage, such as interface debonding and connector fracture, during the loading process. Utilizing the test outcomes, a quantitative relationship between the damage index and slip for the purpose of structural damage assessment has been built. Finally, based on the test data, this study assessed the applicability of current shear resistance design equations, proposed a refined load -slip relationship for studs, and offered well-founded design recommendations.
