A New Type Of Ballastless Track Slab Reinforced With Fiber Reinforced Polymer Bar And Its Basic Performance

Currently,the ballastless track slab systems have been used widely in China and many other countries.Compared with a ballasted track slab system,ballastless track slab system exhibit higher stability,higher durability,and lower maintenance.However,several studies point out that the ballastless track slab cannot be compatible with resonant jointless track circuit used in a ballastless track system.Because a mutual inductance is created between the signal current in the rail and the closed-loop circuit composed of steel meshes in the ballastless track slabs.Thus,the length of the track circuit transmission can be significantly reduced and put a threat to the safety of the track.Several measures have been proposed to improve the insulation property of the steel bars used in ballastless track slabs.Unfortunately,the insulation capability is still reduced and also bond performance between the steel bars and concrete is degraded.Fiber reinforced polymer(FRP)bars has been widely used in various types of repaired and reinforced materials in concrete structures during the past two decades.In addition to non-metallic properties(except for carbon fiber reinforced polymer bars),FRP bars have higher tensile strength,ideal thermal expansion coefficient,better durability and better designability,compared to traditional steel bars.To improve the flexural stiffness and structural ductility of concrete structures,our group also proposed steel-fiber reinforced polymer composite bars(SFCBs).The two materials have shown potential to improve the insulation performance of the ballastless track slabs,and also satify the requirement of structural performance.Based on the above idea,the experimental studies on BFRP and SFCB reinforced ballastless trak slabs were carried out,and the design method of this type of ballastless trak slabs were also investgated.The following conclusions can be drawn:(1)First,the insulation performance of different materials were investigated,the resistances of the reinforcements were tested in single-layer meshes,which were steel bars with sleeves,SFCB and BFRP.Then,the insulation tests of single-layer meshes,double-layer meshes were conducted,after which the insulation tests on the track slabs was carried out.The result shows that resistance of BFRP was independent of voltage and exceeded the megohmmeter range.The SFCB take the second place and had little to do with voltage.In addition,the effect of BFRP-reinforced slabs on the rail resistance increment descended to 26-41%,and the effect of the SFCB slab descended to 70-74%,comparing with traditional ballastless track slabs.Based on the test result,the transmission performance of track circuit was simulated by four-terminal equivalent circuit.(2)Based on the ideal insulation perpority of BFRP and SFCB,the flexural performance of ballastless track slabs was investigated.Four-point and three-point loading tests were conducted on six ballastless track slabs reinforced with different types of composite bars.The test parameters included the types of reinforcing bars,i.e.,SFCBs,BFRPs,and steel bars,and six slabs divided into two series were designed with equal initial stiffnesses before yielding.The failure modes,mid-span load deflection,crack development,and load strains were studied in detail.Based on the experimental results,prediction models also were presented.(3)A total of eleven specimens were tested to evaluate the fatigue performance of ballastless track slabs,which were subjected to constant and variable fatigue loading.The failure modes,load-deflection response,crack width,and strains in reinforcement and concrete are studied in detail.The results shows that The fatigue failure resulted from pre-stressed steel and non-pre-stressed steel rupture for the RC slab and pre-stressed steel rupture accompanied by concrete crushing for the BFRP reinforced slab.The SFCB reinforced slab did not fail in fatigue.The higher maximum load was confirmed to still be safe for the SFCB slab,the SFCBs provided much smaller stress than the steel bars in the RC slabs,and it was easy for the SFCB slabs to meet the limited stress range.Decreased bonding performance occurred in the BFRP slab.Based on the experimental results,the deflection and crack were calculated in reasonable model.(4)Based on the test data,the finite element analysis of nonlinear static performance was conducted,and the constitutive relationship and failure criterion for FRP Reinforced ballastless track slabs were selected.The failure mode,the ultimate strength,the crak and deflection development were studied to verify the reliability of the analytical method.Also the ratio of reinforcement,prestressed degree,and prestressed material were considered as the main parameters,and the deflection development were investigated.Then,the suggested models were prioved for deflection prediction.