Buckling analysis of an innovative type of steel-concrete composite support in tunnels

The steel frame is the main bearing structure that ensures the safety of tunnel construction. Structural damage due to instability is a common occurrence and cannot be ignored. The instability mechanism of the traditional steel arch was analyzed, and an innovative steel frame type called the π-type steel-concrete composite support (π-type SCCS) was proposed to improve the bearing capacity and structural stability. First, the constitutive and interface relations of concrete-filled steel tubes were verified. Then, the buckling model of the π-type SCCS was established by considering the effect of geometric and material nonlinearity. The characteristic parameters of the steel frame were comprehensively analyzed regarding the instability mode, internal force development, and stress variation and were optimized under different construction states. In addition, the influence of different parameters on the structure stability was clarified, including the design of the steel frame and the grouting reinforcement. Finally, the influence of the wall thickness and geometric imperfections on the stability of the π-type SCCS during local buckling was investigated. The results can provide a theoretical basis and references for highly stable tunnel support design