Research Of The Fire-resistant Properties Of The Hollow Concrete Lining Structure In Highway Tunnel

With the development of highway projects, more and more tunnel can be constructed. At the same time, the probability of tunnel fire increases. As a hazard, tunnel fire influences the traffic and threatens the security of people's life and property. It is also a focus of the domestic scholars. As an important part of tunnel, the lining structure fireproof plays an important role in tunnel fire prevent engineering.In this paper, the hollow concrete lining structure is designed to improve the mechanical characteristic of lining in fire. The mechanical characteristic of hollow tunnel lining in fire was studied depending on a tunnel project. The contents of this paper are as following:(1)the mechanical characteristics of hollow tunnel lining at room temperate;(2)the temperature distribution in hollow concrete tunnel lining at high temperate;(3)the mechanical characteristics of hollow concrete tunnel lining at high temperature.On the basis of theoretical analysis an FEM simulation, a series of understanding and valuable findings are achieved in this paper:1. The mechanical characteristics of hollow concrete tunnel lining at home temperature were studied depended on the actual project. The difference of the mechanical characteristics between hollow concrete tunnel lining and solid concrete tunnel lining was also studied. It can be fined:there are three weak points in hollow concrete tunnel the face by fire, the region between two holes and the region adjoining the holes away from the fire surface of lining.2. The temperature distributions in hollow concrete tunnel lining and solid concrete tunnel lining were both studied. It can be defined.(1)the temperature distribution in hollow concrete tunnel lining has the same character to solid concrete tunnel lining. At the initial stage of fire, the temperature difference is the biggest on the heated side of lining, and gradually becomes small towards to the reverse side. At this time, the region affected by temperature is narrow. The temperature difference reduces in the surface region of lining, and increases in the internal region of lining over time. And the region affected by temperature expands over time too.(2)The temperature distribution is layered homogeneous in solid lining, and wave-shaped in hollow tunnel lining. The temperature on the section cutting the hole is higher than that on the section between the holes in the region between the surface of hole and the heated side of lining. And the law is opposite in the region at the other side of the hole.(3)On the section cutting the hole, temperature difference in the hollow lining is lower than that in the solid lining.3. The stress analysis of hollow lining structure at high temperature was executed. And the result was compared with the result of solid lining. It is revealed that:(1)the stress distribution along the thickness in hollow lining is same as it in solid lining. In the surface region of lining, the stress is the highest at the initial stage of fire and gradually reduces over time. In the internal region of lining, the stress is small at the initial stage of fire and gradually increases over time.(2)In the hollow lining, the second principle stress is smaller than the third principle stress. In the solid lining, they are approximately equal. And the first principle stress in the region adjoining the flank of hole is tension stress. This can be explained as the holes in the hollow lining provide some space for concrete to swell.(3)Pressure stress concentration and tension stress concentration arise in the region adjoining the holes away from the fire surface of lining in the hollow lining structure. And the stress distribution on the section between the holes should be given more concern. On this section, the concrete is destroyed in the internal region of the hollow lining because of the biggest tension stress exceeds the ultimate tensile strength of concrete.4. The models which can be used in the analysis of Coupled Multiphysics in concrete are introduced. The vapor pressure fields in different thickness of concrete at different time are calculated with a simplified calculation method. The following is revealed:the vapor pressure can be reduced by the method shortening the distance of vapor permeation. Thus it can be seen the vapor pressure in the hollow concrete lining can be reduced obviously in tunnel fire, and the performance of concrete lining can be improved.5. It can be find from the analysis in this paper the holes in the hollow concrete lining can be obtained through embedding polypropylene rods. The work progress is simple. And the cost is small. The behaviors of the hollow concrete lining are not as good as that of solid concrete lining. But it can meet the demand of engineering.