Fire resistance characteristics of steel-concrete-steel structure and reinforced concrete structure in an eight-lane dual-directional super large-span immersed tunnel

In order to obtain the fire resistance of Steel-Concrete-Steel structure(SCS) and reinforced concrete structure(RC) in super-large span cross section immersed tunnel, fire numerical simulation calculation was conducted to analyze the temperature field of SCS and RC in an Eight-lane Dual-Directional immersed tunnel fire by the finite element method. Three-dimensional finite element models of steel and concrete composite structure under different tunnel fire scenarios in terms of reasonable thermal parameters, material model, and correct boundary conditions was established. On this basis, analysis for the mechanical properties of the composite steel-concrete structure under the ISO-834 standard fire was conducted. The results of the study indicate that temperature of RC slab near the fire surface is grew faster than SCS slab in the immersed tunnel fire, and the temperature inside the SCS slab is lower than that of RC slab in the immersed tunnel fire. The temperature at the nearest monitoring point by the fire surface of the SCS slab is 31.3% lower than that at the same position in the RC slab, which is 41% lower in the center of SCS slab. Research result provide a reference to the theoretical studies and practical engineering of SCS extra larger span immersed tunnel fire, and provide support for the fire protection design of SCS structures in practical engineering.