Study On Fire Resistance Test Method Of Shield Tunnel Segment And Joint

Due to the advantages of safety,high efficiency,little impact on the environment and no limitations of ground environmental conditions on excavation,the number and length of shield tunnels are greatly increasing.However,the shield tunnel lining structure is composed of reinforced concrete segments,and the mechanical properties of segment joints is weak and the high-temperature mechanical properties are complicated.Therefore,fire resistance tests are needed to be carried out urgently.Thus,according to the structural characteristics of shield segments,a large fire resistance testing system suitable for full-scale shield tunnel segments was first developed in this thesis.Fire resistance tests and post-fire mechanical tests were carried out for shield tunnel segments and joints to study the effects of fire type(ISO 834,HC and RABT standard heating curve),segment type(standard segment,standard segments joint and capping segments joint)and sealing arrangement on the mechanical properties of shield tunnel segments at high temperatures and after fire.Finally,the fire resistance testing method of shield tunnel segments was explored based on the fire resistance tests and post-fire mechanical tests on shield tunnel segments.The main contents and conclusions are as follows:The fire resistance testing system of full-scale shield tunnel segments was developed.This system mainly includes vertical loading device,horizontal loading device,fixing device,sealing device and protection device.The feasibility of the test device was verified by numerical simulation using ABAQUS finite element software.This fire resistance testing system of full-scale shield tunnel segments is applicable to the fire resistance test of shield tunnel segments in this paper,and can provide the design reference for other large fire resistance testing systems of shield tunnel segments.Fire resistance tests were carried out on seven full-scale segment specimens,and the effects of fire type(ISO 834,HC and RABT heating curves),segment type(standard segment,standard segments joint and capping segments joint)and sealing arrangement on the mechanical properties of shield tunnel segments under high temperatures were compared and analyzed.The experimental results show that under a fire with a fast heating rate and high temperatures,the concrete on the exposed surface of the segment falls seriously,resulting in exposure of a large number of steel bars to fire,which affects the safety of tunnel lining structures.The concrete at 25 mm from the fire-exposed surface in each test exceeds the fire resistance limit stipulated in the "Code for Fire Protection Design of Buildings",but the segment deformation is small and there is no damage phenomenon.It is one-sided and conservative to judge the fire resistance limit of the load-bearing structure in the tunnel only based on the temperature.The setting of hand hole and joint filling play an important role in protecting the nuts and screws of connecting bolts,but have little effect on the temperature development of the watertight rubber.The thickness reduction of segments caused by severe concrete spalling,the integrity reduction of segments caused by a large number of cracks and the open capillary channel left by the evaporation of concrete moisture seriously reduces the impermeability of segments,which affects the safety of tunnel lining structures.Non-fire mechanical tests were carried out on one full-scale shield tunnel segment,and post-fire mechanical tests were carried out on seven full-scale shield tunnel segments.The effects of fire type,segment type and sealing arrangement on post-fire mechanical properties of shield tunnel segments were thoroughly studied.The test results show that the main failure mode of the standard segment is the concrete spalling and caving in the compression zone,and the failure mode of the fire-exposed segment is consistent with that of the ambient-temperature segment.The main failure mode of standard segments joint and capping segments joint is large vertical deformation of segment,rapid variation of joint open angle and decrease of segment bearing capacity.Since the ultimate bearing capacity of standard block segments mainly depends on the performance of concrete in the compression zone,and the fire-induced high temperature has little effect on the concrete in the compression zone,the ultimate load of ambient and fire-exposed standard segments are in a range of 920 to 970 k N,of which the difference is not significant.The high temperature results in a serious decrease in the mechanical properties of concrete in tension zone,which leads to a larger final deformation of segments.Therefore,compared with ambient segment,the vertical and horizontal displacements of fire-exposed segments are larger when they reach the ultimate bearing capacity.Compared with the standard segment,the ultimate bearing capacity of the segment with joints is obviously smaller and the deformation is larger.The sealing arrangement protects the connecting bolt,which alleviates the decrease of the mechanical properties of the connecting bolt under high temperatures in fire and improves the bearing capacity of the segment with joints.Based on the results from fire resistance tests and ambient-temperature mechanical tests on shield segments,the fire resistance testing method of shield tunnel lining segments is put forward.According to this method,the research steps of fire resistance tests on shield tunnel lining structures are as follows:(1)selection of testing types based on the whole process strategy,including normal temperature mechanical test,fire resistance test and post-fire mechanical test;(2)selection of specimens and relevant settings;(3)scientific design of the fire resistance testing system scientifically according to the structural characteristics of shield tunnel lining including heating system,loading system and acquisition system;(4)selection of heating curve where HC heating curve is recommended;(5)comprehensive evaluation of the hightemperature mechanical properties of shield tunnel lining structures through collecting and analyzing the characterization factors of the fire resistance properties of shield tunnel lining structures.