Performance of CRTS-II Ballastless Track–Bridge Structural System Rebars under Fatigue Loading Test

Lingyu Zhou,Yahui Yuan,Lifan Zou,Yongzhi Gong,Akim D Mahunon,Lei Zhao

doi:10.3390/app11114858

Abstract

To study the evolution of mechanical properties of steel rebars in the China Railway Track System Type II (CRTS II) ballastless track–bridge structural system under repeated train loads, a 1/4 scale three-span ballastless slab track simple-supported bridge structural system specimen was manufactured and subjected to a multistage fatigue test with 18 million cycles. The experimental results show that the strain amplitude of the steel bar changes proportionally to the fatigue stress amplitude, and there is an obvious strain increase in the loading stage 4, where the fatigue stress amplitude is the largest. During the test, the cumulative strain–amplitude ratio first decreases then increases. At the end of the test, the cumulative strain–amplitude ratio increases by 5.46% and 5.32%, respectively, at L/2 and L/4 sections. The load–strain curve of the steel rebar keeps the shape of an oblique straight line. The slope increases first and then decreases with a degradation at the end of the test of 5.15% and 4.81%, respectively, at L/2 and L/4 sections. The mechanical properties of the rebar are enhanced under the first three million fatigue loading cycles: this is the fatigue strengthening stage. The mechanical properties of reinforcement gradually degrade from the three millionth cycle to the end of the test: this is the fatigue damage stage. Finally, based on the material fatigue damage model and the multistage cumulative damage criterion, the change rule of the load–strain curve slope of steel rebars in the fatigue damage stage is obtained by finite element simulation. The simulation results agree well with the experimental data, proving the validity of the calculation method proposed in this paper.

Highlights

High-speed railways have the advantages of strong transportation capacity, high speed, safety and high efficiency, and have been widely used in China in recent years [1,2,3].At present, the length of the high-speed railway bridges that have been built and are under service in China accounts for nearly 50% of the total operating mileage
The fatigue damage process of the steel rebars was simulated by the finite element method, and the following conclusions can be drawn: 1
The strain amplitude of the steel rebar changes proportionally to the fatigue load amplitude, and there is no obvious increase in the strain amplitude under loading stages 1, 2 and 3

Summary

Introduction

The length of the high-speed railway bridges that have been built and are under service in China accounts for nearly 50% of the total operating mileage. The length of simple-supported box girder bridges with a 32 m standard span accounts for about 95% of the total length of constructed bridges [4]. The repeated train load is the main load on the high-speed ballastless track simple-supported box railway girder bridge structural system [5]. Under the long-term train load, the change in the mechanical properties of longitudinal rebars has an important impact on the mechanical performance of the track–bridge structural system. It is of great significance to study the real deformation process, mechanical characteristics and damage evolution of the tensile rebars of the ballastless track simple-supported box girder under a repeated train load

Methods

Findings

Discussion

Conclusion