Acid-induced degradation of interfacial behavior and load capacity in UHPC–SCS composite members: Experimental evaluation and numerical modeling

Steel-concrete-steel composite (SCS) deep beams are increasingly used in marine and underground infrastructures due to their high load-bearing capacity and construction efficiency. However, their long-term durability is severely challenged under acid corrosion conditions, leading to interfacial degradation and premature failure. To address this issue, ultra-high-performance concrete (UHPC) was introduced to enhance the corrosion resistance and mechanical performance of SCS composite deep beams. Push-out tests were first conducted to investigate the interfacial behavior between the steel plate and concrete under acid corrosion. The failure mechanisms and damage modes were analyzed, revealing that UHPC effectively resists acid-induced deterioration and maintains interfacial integrity. Subsequently, beam tests were performed to evaluate the structural performance of SCS composite deep beams with UHPC after acid exposure. The results demonstrated that UHPC significantly improves the load-bearing capacity, alters the failure mode, and effectively prevents interfacial slip. Furthermore, finite element analyses were carried out to perform a comprehensive parametric study. Based on these results, an extended strut-and-tie model was developed, which quantitatively accounts for the effects of interfacial slip, steel plate utilization, beam height, and shear span ratio. The proposed model provides accurate predictions of the ultimate capacity under different failure modes and offers valuable guidance for the design and durability assessment of SCS composite deep beams in corrosive environments.