Experimental study and finite element analysis on interfacial mechanical behaviors of steel-UHPC composite structures in acidic environments

Steel-concrete-steel (SCS) composite structures with ultra-high performance concrete (UHPC) are recognized for their durability and versatility, particularly in harsh environments such as acidic conditions. This study investigates the mechanical behavior at the steel-UHPC interface in SCS systems, focusing on the performance of studs as shear connectors under acidic exposure. Push-out tests were conducted to analyze mechanical performance and failure mechanisms at the interface. The results show that UHPC enhances mechanical performance by 65.4 %, improves ductility by 97.6 %, and significantly reduces crack propagation, offering greater resistance to acidic conditions compared to ordinary concrete. These findings highlight the critical role of UHPC in strengthening the interface and improving durability in aggressive environments. To extend the experimental findings, finite element (FE) analysis was used to develop theoretical models for interfacial shear capacity. A constitutive model integrating machine learning and elastoplastic damage mechanics was introduced to simulate the degradation of UHPC under acidic conditions with high accuracy. The FE model was validated using experimental data, providing detailed insights into the load transfer mechanisms at the interface. By combining experimental and theoretical approaches, this study develops a predictive model for interfacial shear capacity, offering practical guidance for designing durable and reliable SCS systems in demanding environments.