Study on the High-Temperature Mechanical Behavior and Parameters of Joints: a Case of a Prefabricated Frame Tunnel

Joints are the weak parts of the prefabricated frame tunnels, and their mechanical behavior under high temperature conditions is not clear. In this research, a thermal-mechanical coupling numerical model of the tunnel joint is established with reference to an actual assembled frame tunnel. The flexural and shear performance of the joint at room temperature and high temperature are investigated. The effects of axial force, steel plate thickness, steel box thickness, bolt diameter, concrete strength and steel bar diameter on the mechanical properties of the joint are analysed, and the importance of these parameters is evaluated by grey relational analysis. The results show that the flexural and shear bearing capacities of this type of joint decrease significantly at high temperature. The longitudinal rebar diameter and concrete strength play a leading role in the bending capacity of the joint. The concrete strength and steel plate thickness play a dominant role in the shear capacity of the joint. The combination of steel plates and bolts limits the dislocation displacement of the joint, especially when the steel plate thickness is 30 mm, and the shear capacity of the joint significantly improves. The study results can support the fire resistance design of prefabricated tunnels.