Mechanical Behavior Analysis of Tunnel Steel Support with Stirrup Confinement under Small Eccentric Compression

To address the problems in tunnel primary support where slip tends to occur between section steel and concrete—resulting in insufficient structural bearing capacity, poor deformation compatibility, and buckling deformation of steel arches—considering that tunnel support structures are often subjected to eccentric compression, a steel-concrete composite support structure is proposed in which stud shear connectors and stirrups are welded to the steel framework. Eccentric compression tests and numerical simulations are conducted to evaluate the load-carrying performance of specimens with natural bond and specimens with welded studs and stirrups. The results show that, compared with the naturally bonded specimens, the composite structure with welded studs and stirrups increases the ultimate bearing capacity by 31.55%, increases the ductility coefficient by 46.41%, and reduces the lateral deflection by 37.72%. In the naturally bonded specimens, the section steel and concrete slip and separate when the load reaches 60% of the ultimate load; in contrast, welded studs and stirrups effectively enhance the interfacial bond performance between the section steel and concrete and confine the concrete in the core zone, so that the section steel and concrete can still deform compatibly when the specimens reach the ultimate bearing capacity. The numerical simulation results further verify the load-carrying characteristics of the support structure with studs and stirrups, which are consistent with the experimental conclusions.