Influence Of The Fire On Mechanical Properties Of Composite Segment Lining Of Shield Tunnel During Operation Period

Due to its advantages of large buried depth,long distance and diversified sections,shield tunnels have certain advantages in the construction and application of major infrastructure such as underground traffic and underground utility tunnel.At present,composite segment has been developed for complex conditions,such as high water pressure and high soil pressure,as well as for shield tunnels with diversified cross sections,such as ductile reinforced composite segment(DRC segment)and steel reinforced composite segment.Due to the narrow space enclosed by the tunnel structure,once the fire occurs,the temperature inside the tunnel rises instantaneously,causes a large number of casualties,and continuous high temperature will cause great damage to the tunnel lining structure,reduce the bearing capacity of the tunnel lining structure.The composite segment is made up of external steel plate(or ductile iron plate),inner filled concrete and steel bar.The steel plate as the main component is exposed to high temperature,compared with the reinforced concrete structure with concrete protective layer,there are obvious differences in its fire resistance.Based on the existing tests,theoretical analysis and numerical simulation are used to analyze the influence of fire on the mechanical properties of composite segment lining of shield tunnel during operation period.Three dimensional numerical models are established by ABAQUS.The temperature distribution,deformation law,bearing capacity and damage mode of composite segments,joints and lining rings under high temperature are analyzed by RABT heating curve.Then,the difference in high temperature performance between plain concrete segment and composite segment is compared,and the thickness of fire protection layer is suggested.The basic conclusions of this study are as follows: Under RABT heating curve,the radial displacement of lining ring can be divided into three stages,and when the ring is restrained by rigid body,the reaction force of rigid body increases first and then decreases.After RABT heating curve,the vertical bearing capacity of the lining ring decreased by about 45.2%,and the horizontal bearing capacity decreased by about 28.6%.The hand hole has the highest temperature and the most serious damage in the case of fire,and the changes of concrete damage are mainly divided into three stages.And the changes of concrete damage at the composite segment joint can be divided into two stages.The quality of composite segment can be guaranteed to a certain extent when 10 mm thick coated steel structure fire protection coating is adopted.The composite segment structure has a good inhibition effect on the damage of concrete under fire.In the same fire case,the concrete stiffness damage at the inner side of the lining of the plain concrete segment is about 2.9 times that of the composite segment.