Structural performance of ballastless track slabs reinforced with BFRP and SFCB

doi:10.1016/j.compositesb.2014.11.002

Composites Part B: Engineering

Volume 71, 15 March 2015, Pages 103-112

https://doi.org/10.1016/j.compositesb.2014.11.002 Get rights and content

Abstract

Because of the inductive impedance caused by steel meshes in traditional reinforced ballastless track slabs, the electrical properties, primarily the rail resistance and inductance, of jointless track circuits are affected by electromagnetic induction between the slabs and the electric current in the rail. This problem results in poor transmission performance throughout the track circuit. Insulating sleeves or cards between the steel meshes have been used to improve the insulation capability of steel meshes in slabs; however, they reduce the bonding performance between the steel bars and concrete. Because of the good insulation properties of fiber-reinforced polymer composite bars (FRPs) and steel-fiber reinforced polymer composite bars (SFCBs), these composite materials have shown potential to overcome this insulation problem. However, the structural performance of the ballastless track slabs reinforced by basalt fiber reinforced polymer composite bars (BFRPs) and SFCBs, which play a key role in the structure and transportation safety, needs to be investigated. In this paper, six ballastless track slabs reinforced with BFRPs, SFCBs, and steel bars were constructed and tested. The following results were obtained. (1) Shear failures were observed for all slabs, both the BFRP and SFCB slabs meet the load level requirements, and SFCBs reinforcements have higher strength utilization compared with BFRPs reinforcements. (2) The bond-quality of SFCBs and BFRPs reinforcements proved slightly poorer than that of the steel bars. Because of the good corrosion resistance of the FRP, the maximum crack width limits can be slightly larger than that of the RC slabs. (3) Bischoff’s equation was initially used to calculate the deflection of partially prestressed concrete slabs under service loads. The results demonstrated a good agreement between the theoretical and experimental analysis. (4) Considering the tensile stiffness, the modified ACI equation was used to calculate the slabs’ crack width and the theoretical and experimental results showed a good agreement.

Introduction

Compared with a ballasted track slab system, a ballastless track slab system exhibits better performance in terms of stability, durability, and maintenance in high-speed railways [1]. In the ballastless track system, a resonant jointless track circuit is commonly used for high-speed railways in China and Korea. The closed-loop circuit, which consists of longitudinal and transverse reinforcements in the ballastless track slabs, significantly reduces the transmission performance of the track circuit because a mutual inductance is created between the ballastless track slabs and the electric current in the rail; thus, the effect on the electrical properties (the rail resistance and inductance) of the rail poses a significant problem [2], [3], [4], [5], [6]. Hence, numerous measures have been undertaken to improve the insulation property of the steel bars, i.e., painting an insulation coating onto steel meshes, applying heat-shrinkable sleeves, or using insulating cards [2], [6]. Unfortunately, the insulation coating is easily broken in the process of constructing the ballastless track slabs, and the insulation capability is reduced as a result. In addition, the bonding performance between the steel bars and concrete tends to deteriorate, and the cost of labor is higher due to the complex construction technology [6].

Fiber-reinforced polymer composite bars (FRPs), which are composed of non-metallic materials, provide good insulation performance (except for carbon-fiber-reinforced polymer composite bars (CFRPs)), better anti-corrosion properties, higher tensile strength, and a lighter weight compared to ordinary steel bars [7], [8], [9], [10], [11]. The use of FRPs to replace steel bars is an effective approach to solve insulation problems associated with steel bars. Unfortunately, the modulus of elasticity for the FRP bars is relatively low compared to that of steel bars, and thus, the serviceability performance of the flexural member will reduced. Wu et al. [12] proposed steel-fiber-reinforced polymer composite bars (SFCBs) to improve the stiffness and ductility of the concrete structure. The SFCB consists of a combination of steel bars and FRP produced using a complex integrated pultrusion technique [12], [13], [14], [15]. With good insulation properties, a relatively high modulus of elasticity, and good bonding quality, these bars are suitable for reinforcing ballastless track slabs. In this study, a basalt-fiber-reinforced polymer composite bar (BFRP) is added to the steel bars in the SFCB due to its good insulation characteristics and high performance-to-price ratio.

The insulating nature of BFRPs and SFCBs potentially allow improve insulation performance and are attractive to the ballastless track system construction industry. To the best of the authors’ knowledge, the structural performance of track slabs reinforced with BFRPs and SFCBs have not yet been reported in the literature. Therefore, this study provides experimental data for use by engineers in the design and evaluation of the performance of ballastless track slabs reinforced with BFRPs, SFCBs, and traditional steel bars, respectively.

Section snippets

Configuration of ballastless track slabs

A typically constructed CRTS II (Chinese rail transit summit type-II) plate-type ballastless track slab is shown in Fig. 1(a). The slab is 6450 mm long × 2550 mm wide × 200 mm deep and consists of 10 small slabs with a pair of bearing rail stations. The three injection gaps in the figure were used to grout cement asphalt mortar. Following Technology Fund No. 173 [16], the dimensions chosen for the study of the structural performance of the slabs were 2550 mm long × 650 mm wide × 200 mm deep (Series S-KZ), as

Test results

Railway Construction No. 754 [19] does not provide a unified load value for the design of ballastless track slabs because the slabs are applied under different load conditions (tunnel, sub-grade, and bridge). However, the criteria for designing slabs in Japan and Germany are introduced by Railway Construction No. 754 [19]. For the service load level, the criteria from Japan and Germany both use 1.47 times the static wheel load; however, a value of 1.57 times the static wheel load was obtained

Review of existing codes used to predict shear capacity

To calculate the shear bearing capacity for prestressed members, both ACI 318-11 [23] and PCI 2010 [24] use the same method, as shown in Eq. (1). Factor λ reflects the lower tensile strength of lightweight concrete. For normal-weight concrete, λ = 1.0, f_c′ (=0.8 f_cu) is the cylinder compressive strength of concrete [25], f_cu is the cubic compressive strength of concrete, b and b_w are the width and web width of member, respectively. d_p is the distance from the extreme compression fiber to the

Conclusions

To improve the insulation and anti-corrosion properties of ballastless track slabs, BFRPs and SFCBs were used to reinforce the slabs, and the flexural performance 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

Acknowledgements

The authors acknowledge the financial support from the National Program on Key Basic Research Project (No. 2012CB026200), the Key Project of Chinese Ministry of Education (Grant No: 113029A), the National Natural Science Foundation of China (Grant No: 51178099) and the Project funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD).

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Citation Excerpt :
The deflection and ultimate capacity were 8.19 mm and 300 kN for slab S-RC1, and 7.38 mm and 254 kN for slab S-RC2, respectively. The details of the static test process of the slabs were reported in Ref. [13], and the obtained test results are shown in Table 2. Pcr, Δy, Δru, Pru, Δu and Pu are the cracking load, yield displacement, residual ultimate deformation, residual ultimate strengths, ultimate displacement and ultimate load of each slab respectively, and the displacement ductility coefficient is defined as μΔ = Δu/Δy.
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Structural performance of ballastless track slabs reinforced with BFRP and SFCB

Abstract

Introduction

Section snippets

Configuration of ballastless track slabs

Test results

Review of existing codes used to predict shear capacity

Conclusions

Acknowledgements

Compos B Eng

Compos B Eng

Compos B Eng

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J Korean Soc Railway

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China Civil Eng J

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ACI Struct J

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