Abstract: Comparative test is conducted on mechanical properties such as ultimate bearing capacity, flexural stiffness, bending deflection, and failure form of the traditional lattice girder and the selfdesigned fourbar steel tube frame support structures under individual load and common load conditions using Abaqus general finite element software and comprehensively considering the thickness of the steel tube, member weight, material cost and other influencing factors. The results show that: (1) The flexural stiffness, bearing capacity, deformation, and failure form of the steel tube frame are different from those of lattice girder. In the case of similar steel weight, the steel tube frame has higher strength and flexural stiffness, meanwhile, the structural deformation and stress are also rational. (2) The bearing capacity of the steel tube frame is significantly affected by the thickness of the steel tube. The bearing capacity decreases with decreasing steel tube thickness. When the thickness reaches a certain value, continuing to increase the thickness will have limited effect on improving the overall strength and bending stiffness of the component, and will increase the weight and material cost of the component accordingly. (3) Under the condition of single load, the bearing capacity of lattice girder is 44.5 kN·m, which is 39.3% lower than that of PG-2 steel tube frame. Under this condition, the weight of the steel tube frame is slightly lower than that of the lattice girder, and the unit price per linear meter is higher. (4) The ultimate load of the lattice girder concrete member is 174.6 kN·m, which is 2.7% and 30.6% lower than the steel tube frame concrete members C+PG-2 and C+PG-6, respectively. (5) The steel tube frame has good applicability to the surrounding rock with a large deformation rate at the early stage.

Key words: tunnelling, steel tube frame, lattice girder, the bearing capacity, bending stiffness, finite element simulation