•A refined prediction method for the long-term performance of BFRP bars.•The effects of service year, concrete-wrap, environmental humidity and seasonal temperature fluctuations are considered.•The environmental reduction factors for a BFRP bar are predicted.A new kind of advanced composite reinforcement, basalt fiber reinforced polymer (BFRP) bars, has not yet been widely adopted by design codes/guidelines worldwide, likely due to the lack of reliable long-term performance data. This paper proposed a refined prediction method for the long-term performance of BFRP bars that considers the effects of service year, concrete-wrap, environmental humidity and seasonal temperature fluctuations. According to the available accelerated aging tests data in the literature, the environmental reduction factors (ERFs) for a BFRP bar used as a concrete internal reinforcement in a field environment are predicted. The results showed that the ERF for BFRP bars can be recommended to be 0.84 or 0.72 for an RH < 90% and a moisture saturated environment (RH = 100%), respectively.

This paper presents experimental and numerical results of concrete columns reinforced by longitudinal steel basalt fiber reinforced polymer (FRP) composite bars (SBFCB) and lateral stirrups steel-wire basalt FRP (BFRP) composite stirrups (SWBFCS). The main parameter is the un-bonded length of the SBFCB and concrete in the column base. Both SBFCBs and SWBFCSs consisting of inner steel bars or wires hybrid with outer BFRP. The axial compressive loading test of concrete cylinders confined by SWBFCS demonstrated the effective confinement of this new kind of stirrup. Moreover, in this paper, the bond relationship between the concrete and the SBFCBs was measured in three bridge columns. One column was utilized as a reference, and the other two with un-bonded lengths of 150 mm and 300 mm, covering the plastic hinge region above the column base. The hysteretic behavior, energy dissipation capacity, residual displacements, and curvatures of the three columns were analyzed. The results show that the maximum load of the proposed specimen with a 300 mm un-bonded length is increased by 15.8%, and the residual displacement was 9% smaller than that of the of the control specimen because of the un-bond length between concrete and SBFCB.

•SFCBs have excellent bond with both sea sand concrete and river sand concrete.•The chloride ions contained in sea sand improve the bond durability of SFCBs.•The bond degradation of SFCBs in immersion is greater than in wet–dry cycling.•Bond degradation with time for SFCBs in sea sand concrete should be convergent.Bond durability tests on steel-fiber reinforced polymer (FRP) composite bars (SFCBs) with sea sand concrete and river sand concrete in simulated ocean environments are conducted in this paper, and steel bars are also used for comparison. Two types of environments, seawater immersion and seawater wet–dry cycling, are adopted. Sixty-six pullout specimens are prepared, and the variations of bond performance after 30, 60 and 90 days of aging are tested and comparatively analyzed. The test results showed that, with respect to the bond–slip curves, wave-shaped descending branches were observed for SFCBs; the bond strength between SFCBs and sea sand concrete in a wet–dry cycling environment at all ages were improved. However, with regard to the steel bars in the same condition, the surfaces were rusted, and the bond strengths showed a decreasing trend. Immersion in 40 °C seawater reduced the bond performance of SFCBs with concrete, whereas the rust process of steel bars slowed down due to the lack of fresh oxygen.

•Steel-fiber reinforced polymer composite bar (SFCB) was introduced into ballastless track slabs.•SFCBs potentially allow increased service life as well as economic and environmental benefits.•Traditional construction technology is simplified and the cost of labor maybe reduced.•Insulating test results were compared and suggestions toward a widespread use of SFCB.•Insulating test results provide experimental data for designing ballastless track slabs.Due to inductive impedance caused by steel meshes in traditional reinforced ballastless track slabs, the electric properties, primarily rail resistance and inductance, of the track circuit are affected by electromagnetic induction between the slabs and the electric current in the rail. This problem results in poor transmission performance through the track circuit. Insulating heat-shrinkable sleeves 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 highly insulating properties of fiber reinforced polymer (FRP) and steel-fiber reinforced polymer composite bar (SFCB), these composite materials have shown promise to overcome the insulation problem. In the study reported in this paper, single and double layer meshes and ballastless track slabs were manufactured and tested for the first time. In the research reported herein, basalt fiber reinforced polymer (BFRP) and SFCB were used in meshes and slabs, respectively. The electric properties of the rail affected by these meshes and slabs were investigated and compared with steel meshes and ordinary reinforced ballastless track slabs (RC). As the test results demonstrated, the signal frequency and distance between the slabs or meshes and the rail had a significant impact on the electric properties of the rail. Furthermore, the variation in rail resistance induced by the slabs or meshes increased drastically, while the change in rail inductance increment varied slowly. BFRP and SFCB used as transverse reinforcement of slabs or meshes reduced the variation in the electric properties of the rail. BFRP reinforced ballastless track slabs had the highest insulating performance, while those with SFCB demonstrated the second highest performance.

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.

The novel concept of this paper is to investigate the required recoverability of existing important reinforced concrete (RC) bridges retrofitted with fiber-reinforced polymers (FRP) to restore their original functions after a moderate or strong earthquake. Hence, this paper presents an up-to-date literature search on the inelastic performance of 109 FRP-retrofitted columns with lap-splice deficiency, flexural deficiency, or shear deficiency. The study is conducted in the following steps: using post-yield stiffness as a seismic index, the effectiveness of FRP jackets in enhancing the inelastic stage performance of non-ductile reinforced concrete columns is scrutinized for the available database; the performance of columns which successfully achieved post-yield stiffness is categorized in accordance with the required recoverability after an earthquake; and according to the definition of a controllable recoverable structure, the appropriate composite jacket thickness is calculated. In the view of a proposed mechanical model of an FRP–RC damage-controllable structure, 61 columns of the available database exhibited idealized lateral performance with stable post-yield stiffness, or secondary stiffness. Lateral drift at the end of the recoverable state is defined from the hysteretic responses of 39 columns and is visualized as a ratio of column lateral drift by the end of the post-yield stiffness with explicit consideration for the effect of both column cross-section shape and deficiency. Finally, suitable FRP design assumptions and concepts certifying the reality of post-yield stiffness are given. Furthermore, in the light of Seismic Design Specifications of Highway Bridges in Japan, a FRP strengthening design guideline that considers and evaluates structural recoverability is proposed.

A good modeling of the stress–strain behavior of FRP-confined concrete prism is necessary for the design of rectangular columns retrofitted with FRP composites. Existing stress–strain models for FRP-confined concrete prisms are mostly presented based on the concept of steel-confined concrete columns. Based on the results of more than one hundred specimens, the mechanical behavior of FRP-confined concrete prisms are studied in this paper. It is found that the stress–strain relationship of FRP-confined prism has either a strain-hardening or a strain-softening response, which mainly depends on the confinement strength of FRP, corner radius of cross-section, etc. Equations to predict the transitional stress and strain of FRP-confined concrete prisms are presented. By reducing the corresponding ultimate strength and strain of equivalent concrete cylinders confined with equivalent FRP, the ultimate strength and strain of FRP-confined concrete prisms can be predicted rationally. Three design-oriented models, which can be applied to various conditions, are suggested. The feature of those models is simple, and they agree well with extensive experimental results.

Based on results from more than 300 specimens of fiber reinforced polymer (FRP) confined concrete cylinders covering a wide range of parameters, the confinement effect and failure mechanisms are analyzed. Special attention is given to predict whether FRP-confined concrete cylinder has a strain-hardening or a strain-softening response. In the case of FRP-confined concrete cylinder with a strain-hardening response, it is found that the ultimate Poisson’s ratio of FRP-confined concrete trends to an asymptotic value. Through calculation of the ultimate Poisson’s ratio, and according to strain compatibility, the ultimate strain of FRP-confined concrete can be predicted. Moreover, by comparing with a lot of existing experimental data, the proposed models are quite simple and still accurate enough, which can be applied to the concrete cylinders confined with various types of FRP composites. Besides, for the case of FRP-confined concrete cylinder with a strain-softening response, equations for predicting the maximum strength, peak strain, ultimate strength and ultimate strain are suggested in this paper.

•We tested four concrete columns under cyclic loading.•The reinforcements including steel bars, hybrid steel/FRP bars, and SFCBs.•The failure modes and hysteretic behaviors were analyzed.Effective post-yield stiffness of reinforced concrete (RC) columns can significantly contribute to the seismic performance of RC structures. However, because of the elastoplastic properties of steel bars, the post-yield stiffness of an ordinary RC column can be very slight or even negative. Fiber reinforced polymer (FRP) can provide a high degree of ultimate strength, light weight, and protection from corrosion. By combining steel and FRP, a designable post-yield stiffness can be achieved for concrete structures reinforced with steel-FRP composite bars (SFCBs) or hybrid steel/FRP bars. This paper conducted cyclic loading tests on four concrete columns with different reinforcement types, including steel bars, hybrid steel/FRP bars, and SFCBs. The test results showed that (1) the columns reinforced with different bars had similar strain distributions from column base to cap prior to yielding. After yielding, the plastic deformation of the ordinary RC column concentrated at the column base and the loading capacity decreased with the increase of lateral drift because of the P-δ effect. (2) Unlike the negative post-yield stiffness of an ordinary RC column, the post-yield stiffness of a column with hybrid reinforcements was positive. As the post-yield stiffness ratio of the longitudinal reinforcement increased by 27 percent, the post-yield stiffness of the concrete column increased by 7.4 percent. Therefore, the corresponding displacement ductility could reach 11—much greater than that of the RC column (6.28). (3) As a result of the more robust hysteretic curve of the RC column, the equivalent viscous damping coefficients of the RC column were greater than those of the hybrid column, whereas the hybrid reinforced concrete columns could dissipate earthquake energy without a corresponding loss of strength.