Simulation of Thermomechanical Coupling and Evaluation of the Fire Resistance for the Joints of Fabricated Frame Tunnel

Fire in a tunnel will deteriorate the mechanical properties of the tunnel. For fabricated tunnels formed by splicing prefabricated components through joints, under the high temperature of a fire, the rapid degradation of the bearing capacity of the joints can easily lead to tunnel damage. In this study, a new type of joint (bolt-pin joints (BPJ)) for prefabricated frame tunnels is proposed. To investigate the fire resistance of the new joint and the other three fabricated frame tunnel joints (including mortise joints (MJ), bolt-mortise joints (BMJ), and pin joints (PJ)), a three-dimensional solid model of four types of fabricated frame tunnel joints is established using the finite element calculation software ABAQUS. According to the standard European HC curve, the heat transfer characteristics of the joint model are analyzed, the temperature distribution law of the joint under fire is studied, and the flexural bearing performance and deformation characteristics of the joint before and after the fire are discussed, as well as the influence of the initial axial force on the flexural bearing capacity and the opening of the joint under fire. The analysis result shows that the vertical peak load of the BPJ is higher than that of the other three joints at room temperature. Under the combined action of the pin and bolts and the tongue groove, the vertical peak load of the joints can be effectively increased and the midspan vertical displacement can be reduced. The decrease degree of the vertical peak load of the MJ and BMJ under fire exposure is greater than that of the other two joints, and the opening of the BPJ is 19 mm, which is much smaller than that of the other three joints. When the initial axial force is increased, the openings of the four joints under fire exposure are reduced, the vertical peak loads of the PJ and BPJ are increased, and the vertical peak loads of the MJ and BMJ are not significantly increased. Overall, the BPJ demonstrates better fire resistance.