Basalt Fiber-reinforced Polymer Tendons Research Articles

Structural design of self-centering socket precast post-tensioned segmental (SSPPS) bridge piers reinforced with BFRP tendons and stainless energy dissipation bars

In order to solve the construction and seismic problems of the existing precast pier connection methods, a self-centering socket precast post-tensioned segmental (SSPPS) bridge pier reinforced with basalt fiber reinforced polymer (BFRP) tendons and stainless energy dissipation (ED) bars is proposed. A detailed finite-element (FE) model is developed, validated with experimental results, and a parametric analysis of SSPPS is carried out. The bending performance, shear performance, anti-opening and closing and anti-overturning performance of the SSPPS pier are assessed through the simplified mechanical analysis. The findings demonstrate the SSPPS bridge pier is distinguished by its convenient construction and remarkable post-earthquake self-centering performance.

Post-tensioned steel beam-column connections with reduced length BFRP tendons

The seismic behavior of the traditional top and seat angle beam-column connection was experimentally evaluated using a half-scaled prefabricated exterior beam-column connection subassembly. Then, an ensemble of three post-tensioned beam-column connections using reduced length basalt fiber reinforced polymer (BFRP) tendons was tested with three different tendons' post-tension (PT) force levels of 15.9, 30, and 50% of the tendons' ultimate strength. Following that, another group of three additional subassemblies containing both reduced length BFRP tendons, as post-tensioning devices, and top and seat angles, as energy dissipation (ED) devices, was tested with the same three post-tension force levels used in the previously tested group. Finally, an analytical model was proposed to capture the moment-relative rotation response of the traditional top and seat angle and the connection combining both the top and seat angles and the BFRP tendons. The results showed that connections containing BFRP tendons only, with the lowest PT force level, provided the same envelope of the top and seat angle connection, and further enhancement could be achieved by increasing the PT force level. Also, the addition of the BFRP tendons to top and seat angle connection improved the connection strength, initial stiffness, post-yield stiffness, and reduced the residual drift. In addition, the proposed analytical model predicted the moment-relative response well, which ensures the reliability of the model in designing such connections.

Optimization of anchorage and deviator for concrete beams prestressed with external fiber-reinforced polymer tendons

This paper focuses on the optimization of anchorage and deviator for concrete beams prestressed with external basalt fiber-reinforced polymer (BFRP) tendons. A composite-wedge (CW) anchorage for BFRP tendons was first developed. The dimensions of the wedge were optimized using finite element (FE) analysis. Additionally, a three-dimensional deviator-tendon FE model was established, and the ratio of the curvature radius of the deviator to the radius of the tendon (Rd/Rp) and the bending angle (θ) of the BFRP tendon were optimized. Furthermore, an experimental study on the flexural behaviors of a non-prestressed concrete beam and a beam prestressed with external BFRP tendons was conducted. The results show that the proposed CW anchorage achieved an anchor efficiency factor of 85%. The recommended lower limit value of Rd/Rp is 200, and the upper limit value of θ is 5°. The RC beam prestressed with external BFRP tendons exhibited enhanced flexural behaviors, compared with the non-prestressed RC beam. The BFRP tendons at the anchor zones and tendons at the deviators remained intact at the ultimate load of the beam. The results validate the effectiveness of the anchorage and deviator parameters.

Long-term mechanical behaviors of uncracked concrete beams prestressed with external basalt fiber-reinforced polymer tendons

In this study, an experiment was conducted on four uncracked concrete beams prestressed with external basalt fiber-reinforced polymer (BFRP) tendons or stress-relieved strands subjected to 300-day sustained loads. The experimental variables included tendon type, prestress level (40 kN and 50 kN), and concrete strength grade (C40 and C60). The effects of these variables on the long-term deformation and prestress loss of the beams were discussed and analyzed. Based on an existing approach using an age-adjusted effective modulus method (AEMM), a modified model was proposed for predicting the long-term deformation and prestress loss of concrete beams prestressed with external BFRP tendons. The results indicated that the prestress level had significant effects on the long-term deformation and prestress loss. The concrete strength grade significantly affected the long-term deformation, but had no effect on the prestress loss. The stress-relieved strands exhibited a prestress loss that was 16% greater than that of the BFRP tendons. The theoretical results based on the modified model were consistent with the experimental results. The results of this study contribute to the design and prediction of the long-term behaviors of concrete beams prestressed with external BFRP tendons.

Composite-Wedge Anchorage for Fiber-Reinforced Polymer Tendons

A novel composite-wedge anchorage is proposed here for prestressing fiber-reinforced polymer (FRP) tendons. The composite wedge was designed and optimized in terms of the length and elastic modulus of the wedge segments via finite-element analysis. The manufacturing technologies for the composite wedge involving a molding process, are presented in detail. Static, creep, and fatigue tests on basalt FRP (BFRP) tendons with the proposed anchorages were conducted. The tensile capacity, long-term deformation, and fatigue life of the tendon–anchor assemblies were analyzed. The experimental results show that the proposed anchorage exhibits an anchor efficiency factor of up to 91%; the corresponding value for a conventional steel–wedge anchorage is only 80%. The tendon–anchor assembly displays a creep behavior similar to that of BFRP tendons. Furthermore, the system survives 200 million cycles of fatigue load at a maximum fatigue load of 0.5 Fu (Fu is the tensile capacity of the tendon–anchor assembly) and a load range of 0.05 Fu. Wedge–sleeve and tendon–wedge sliding under a sustained load or cyclic load cannot cause considerable prestress loss in practical engineering. The results validate the effectiveness of the proposed anchorage under service loads and demonstrate the application prospects of this anchorage.

Hysteretic Behavior of Dual-Self-Centering Variable Friction Damper Braces with Low Pretensioned Force

ABSTRACT To satisfy the resilient requirements, a novel dual-self-centering variable friction damper (DSC-VFD) brace with self-centering variable friction damper systems and basalt fiber-reinforced polymer tendons, is proposed. The working mechanism of the DSC-VFD brace was first investigated. Then, four DSC-VFD and SC-VFD braces with different groove angles were designed, and quasi-static experiments were conducted. Finally, finite element models of the DSC-VFD braced frame were created and the seismic responses of the frames were analyzed. The results show that the DSC-VFD brace presents a novel flag shape with large post-yield stiffness and enhanced energy dissipation which can effectively control the structural responses.

Theoretical Study on Prestress Loss in Cross-Tensioned Concrete Pavement with BFRP Tendons

Cross-tensioned concrete pavement can reduce transverse joints and cracks and improve the durability of the pavement, and the decrease in slab thickness can be achieved without damaging the performance of the pavement. However, the corrosion of the steel can cause serious damage to the pavement structure, resulting in higher maintenance costs and shorter service life. Basalt fiber-reinforced polymer (BFRP) has been proven to be an effective alternative in both jointed plain concrete pavement (JPCP) and continuously reinforced concrete pavement (CRCP) due to its lightweight and corrosion-resistant properties. In this paper, a systematic theoretical method for determining the prestress loss of BFRP tendons in cross-tensioned concrete pavement was proposed, with the impact of the slab width and distribution angle of the prestressed tendon on the prestress loss being studied and compared to the results of traditional steel strands. Results showed that the proportion of the prestress loss due to anchorage deformation and prestress retraction in the prestressing stage rose with the increase in distribution angle and the decrease in slab width, while the prestress loss during the in-service stage was a constant value for both BFRP tendons and steel strands. The prestress loss of BFRP tendons was far lower than that of steel strands in both prestressing stage and in-service stage for a given slab width (3 m, 4.5 m, 9.0 m, 12.75 m) and distribution angle (20°, 25°, 30°, 35°, 40°, 45°), and the difference ranged from 6.4% to 16%, signifying the feasibility of BFRP tendons in cross-tensioned concrete pavement. Overall, the smaller the slab width, the greater the difference of the prestress loss between BFRP tendons and steel strands.

Tensile mechanical properties of basalt fiber reinforced polymer tendons at low to intermediate strain rates

Basalt fiber reinforced polymer (BFRP) tendons are well known for their day-by-day increasing applications in infrastructural engineering. Advantages like high corrosion resistance, low-cost and environment-friendly features make BFRP tendons one of the best alternatives for metal-based (for example steel) reinforcement. Civil engineering components are always under high risk of earthquake, explosion or any impact/collision situation. Therefore, it becomes necessary to analyze the mechanical properties of BFRP tendons in every aspect of real-life situations. This paper investigates the mechanical properties of BFRP tendons through pullout (at 0.05 mm/s), quasi-static (at 0.05 mm/s) and dynamic (at 1, 3, 5, 10, 5 m/s) tests. The effects of varying loading velocities (or strain-rates) over damage process are characterized by digital image correlation (DIC) method. The micrographs by scanning electron microscopy (SEM) identified the modes of fracture occurred during the experimental tests. The discreteness of failure strength at various strain-rates is analyzed by ‘Weibull distribution: a statistical method’. The experimental investigation proved that the BFRP tendons are highly influenced by strain-rate under tensile loading. As compared to quasi-static tests, the tensile strength is increased by 98% at the strain-rate of 28.98 s−1. It is also estimated that Weibull distribution is one of the best available statistical tools for estimating randomness in BFRP tendons.

Fatigue behavior of basalt fiber-reinforced polymer tendons under a marine environment

Due to their advantageous mechanical behaviors and anti-salt properties, basalt fiber-reinforced polymer (BFRP) tendons are a promising prestressing component under a marine environment. However, the degradation law of fatigue behavior of BFRP tendons under a marine environment is still unclear. This paper studies the fatigue behavior of BFRP tendons after aging in a salt solution by temperature-accelerated experiments. The degradation mechanism of fatigue behavior is clarified based on previous studies and analysis of the failure mode. The effect of aging temperature on fatigue strength degradation is analyzed using both experimental data and scanning electron microscopy (SEM) images. Moreover, the fatigue strength degradation of BFRP tendons at different local temperatures was predicted according to the Arrhenius equation. The results show that the fatigue strength degradation of BFRP tendons is governed by the weakened fiber-matrix interface resulting from the hydrolyzation of Si–O–Si chemical bonds in salt solution. SEM showed that specimens aged at 55°C for 63days demonstrate increased corrosion than those in other groups. Through the Arrhenius equation, the fatigue strengths of BFRP tendons are predicted to be 0.41, 0.43 and 0.45fu, respectively, at three representative northern latitudes after 100years of aging in marine environments. The results provide guidance for fatigue design of BFRP tendons in a marine environment.

Relaxation behavior of prestressing basalt fiber-reinforced polymer tendons considering anchorage slippage

Relaxation is a key factor that controls the application of prestressing fiber-reinforced polymer tendons. This paper focuses on the evaluation of the relaxation behavior of newly developed basalt fiber-reinforced polymer tendons through an approach considering anchorage slippage. A series of relaxation tests on basalt fiber-reinforced polymer tendons subjected to three levels of initial stresses (0.4 fu, 0.5 fu, and 0.6 fu, where fu = ultimate strength) were conducted using a specially designed test setup that eliminates the impact of slippage at the anchor zone. An additional group of tests was conducted to validate the enhancement effect of pretension on the relaxation behavior. The relaxation rates at one million hours were predicted based on experimental fitting. Finally, the relaxation rates at 1000 h were predicted using the correlation between the relaxation and creep and were validated with the experimental relaxation rates. The results demonstrate the effectiveness of the proposed setup in measuring the relaxation loss of specimens and reveal that the relaxation rates of untreated basalt fiber-reinforced polymer tendons at 1000 h are 4.2%, 5.3%, and 6.4% at 0.4 fu, 0.5 fu, and 0.6 fu, respectively. Pretension treatment performs effective in relaxation loss controlling. BFRP tendons are recommended to be applied at an initial stress of 0.5 fu after pretension treatment, with one-million-hour relaxation rate equal to 6.7%. Furthermore, the relaxation rate at 1000 h can be predicted accurately based on the creep behavior. The conclusions of this study can provide guidance for the prestressing applications of basalt fiber-reinforced polymer tendons.

Fatigue Behavior of Basalt Fiber-Reinforced Polymer Tendons for Prestressing Applications

AbstractThis paper studies the fatigue behavior of high-strength basalt fiber-reinforced polymer (BFRP) tendons for potential applications in prestressed structures. An effective anchoring method of winding fiber sheets was first developed for fatigue testing of BFRP tendons to avoid premature failure at the anchorage. The fatigue stress ranges from 0.05 to 0.14fu (fu = ultimate tensile strength) and maximum stresses from 0.6 to 0.8fu were determined, whereas the elastic modulus of BFRP tendons during the fatigue tests was measured. The fatigue failure mechanism was analyzed and elaborated at both the macro- and microscopic levels. The appropriate fatigue stress range and maximum stress level were predicted from both experimental fitting and reliability analysis. The results show that the fatigue failure of a BFRP tendon is mainly induced by the debonding among fiber-matrix interfaces at the outer layer of the tendon. The fatigue stress range greatly affects the fatigue life of BFRP tendons. The BFRP tend...

Creep strain control by pretension for basalt fiber-reinforced polymer tendon in civil applications

Basalt fiber-reinforced polymer (BFRP) is a superior material for prestressing applications owing to its high creep rupture stress of 0.6 fu (fu=tensile strength). This paper proposes a method by pretension to further control the creep strain and lower prestressing loss of BFRP tendons serving as prestressed structural member. Experimental parameters including pretension levels and durations were selected to investigate their effects on creep strain control while creep strain rates and relevant variations were compared among the specimens under different control conditions. Furthermore, the modeling of long-term creep behavior based on a semi-logarithmic equation was also conducted. The results show that the pretension can significantly lower the creep strain of BFRP tendons. The maximum control effect of creep strain can be obtained by a pretension of 0.6 fu with duration of 3h. The above control effects are consistent with the results revealed by the residual strength of the specimens after creep test. The modeling prediction indicates that the creep strain rates at one thousand and one million hours for the BFRP tendon can be controlled to 1.46% and 3.65% under a sustained stress of 0.5 fu.

Effects of radial stress at anchor zone on tensile properties of basalt fiber-reinforced polymer tendons

This paper investigates the effects of radial stresses induced by anchoring component at anchor zone on the tensile properties of basalt fiber-reinforced polymer tendons and proposes allowable radial stresses for design and application. The tensile experiments were first conducted to determine the tensile strength of basalt fiber-reinforced polymer tendons with different types of anchorage including bonding, friction, and compression with protective layer to achieve different levels of radial stresses. The longitudinal compressive strength, transverse compressive strength, and in-plane shear strength of basalt fiber-reinforced polymer tendons themselves were also measured for theoretical prediction. On the basis of experiments, the theoretical analysis by Hoffman strength criterion on ultimate tensile strength of basalt fiber-reinforced polymer tendon was conducted according to the above experimental results while the allowable axial stress for application was studied accordingly. The results show that the radial stress affects significantly on the ultimate strength of basalt fiber-reinforced polymer tendon. The mean values of ultimate strength of basalt fiber-reinforced polymer tendons anchored by friction and compression with different radial stresses are 5, 12, and 15% lower than that of the specimens by bonding anchor. Hoffman strength criterion is proven to be an effective model in predicting the ultimate strength with different anchorages. For 6 mm basalt fiber-reinforced polymer tendon, the radial stresses at the anchor zone are recommended to be below 50 MPa to assure no strength reduction and below 90 MPa with allowable 10% strength reduction. Radial stress is not allowed to exceed 130 MPa to avoid compression failure. The prediction method can guide the design of effective anchorage for the prestressing application of basalt fiber-reinforced polymer tendon.

Creep behavior enhancement of a basalt fiber-reinforced polymer tendon

Creep behavior is a key factor controlling the long-term behavior of basalt fiber-reinforced polymer (BFRP) tendons when employed as prestressing members. This paper studies the creep behavior of pretension-treated BFRP tendons and evaluates its potentials in prestressing applications. Based on an effective enhancement by pretension, the evaluation of the creep behavior of pretension-treated BFRP tendons was conducted. The parameters comprise the creep strain–time relationship, creep strain rates, residual strength and elastic modulus after creep and the prediction of the creep rupture stress based on a reliability analysis. In addition, the creep behavior of pretension-treated BFRP was also compared with the results of original untreated BFRP tendons. The results show that pretension-treated BFRP tendons can sustain a stress level of 0.7 fu without fracture within 1000h, 17% higher than the untreated BFRP tendons (0.6 fu). The creep strain rates of BFRP tendons after pretension exhibit a substantially low level in comparison to those without the pretension process, demonstrating the effectiveness of the pretension on creep strain rate control. The one million-hour creep rupture stress of BFRP tendons is effectively enhanced from the original 0.59 fu to 0.63 fu based on experimental fitting and from 0.52 fu to 0.54 fu according to a reliability analysis.

Effectiveness of basalt FRP tendons for strengthening of RC beams through the external prestressing technique

This paper investigates the feasibility of newly developed basalt fiber reinforced polymer (BFRP) as prestressing material and the structural behavior of reinforced concrete (RC) beams strengthened with externally prestressing BFRP tendons. Three main factors potential controlling structural strengthening effects, including tension stresses, bending angles and anchorages of the tendons, were first discussed based on literature review and finite element (FE) simulation. In the structural experiment, the effects of tension stresses and the tendon profiles on the flexural behavior of RC beams were discussed and the evaluation on the ultimate bearing capacity, cracking moment, crack width and deflection of strengthened beams was conducted by theoretical calculation and experimental results. The results show that the prestressing level of BFRP tendon can be determined to be 0.50fu and 0.38fu (fu is the tensile strength) according to creep rupture limit. The bending angle at the deviator is optimized to be 2° and the bond anchorage with resin epoxy was adopted to maximize strength utilization. For strengthening behavior, the second-order effect of the externally prestressed beam can be effectively relieved by using proper deviators, which is demonstrated by enhanced ultimate capacity. All of the strengthened RC beams are failed by concrete crushing, with satisfactory crack patterns and superior ductility compared to the control beam, which demonstrates the simultaneous working of internal steel reinforcements and external prestressing BFRP tendons during loading. The evaluation on mechanical behavior of strengthened RC beams indicates theoretical calculation according to several existing standards can well predict strengthening effect.

Experimental Investigation of the Hysteretic Performance of Dual-Tube Self-Centering Buckling-Restrained Braces with Composite Tendons

AbstractThis paper presents the results of experimental testing a novel dual-tube self-centering buckling-restrained brace (SC-BRB) with pretensioned basalt fiber-reinforced polymer (BFRP) composite tendons. Cyclic tensile experiments are first conducted on two sets of BFRP tendons with different diameters. The results confirm that the BFRP tendons have a stable cyclic elastic modulus and sufficient elongation capacity, making them suitable for use as the self-centering tendons in SC-BRBs. Quasi-static experiments are performed using two dual-tube SC-BRB specimens with different core plate areas. Before the failure of the self-centering system, both specimens stably exhibit the expected flag-shaped hysteresis response, with a relatively small residual deformation. The internal forces in the BFRP tendons and the gaps between the tubes and the end plates are measured to validate the performance of the self-centering system. Both specimens meet the requirements for ultimate ductility and cumulative ductility...

Evaluation of prestressed basalt fiber and hybrid fiber reinforced polymer tendons under marine environment

This paper studies the degradation of the tensile properties of prestressed basalt fiber-reinforced polymer (BFRP) and hybrid FRP tendons in a marine environment. Two levels of prestressing toward typical prestressing applications were applied in the experiment. The variations of tensile strength, elastic modulus and the relevant coefficient of variation (CV) were first investigated. The effect of prestressing on tensile property degradation was discussed. The characteristics of prestressed hybrid FRP tendons in a marine environment simulated by a salt solution were clarified. Moreover, a prediction model of BFRP tendons with different levels of prestressing in a marine environment was proposed. The results show that the BFRP tendons’ superior resistance to salt corrosion and the degradation rate of their tensile strength is nonlinearly proportional to the prestressing ratios, whereas the elastic modulus remains constant regardless the prestressing ratio and aging duration. Although prestressing on BFRP tendons accelerates degradation, it can still lower the variation of the strength of the BFRP tendon. Hybridization can lower the degradation rate of basalt and carbon FRP (B/CFRP) without prestressing, whereas basalt and steel-wire FRP (B/SFRP) exhibit much faster degradation due to the internal corrosive steel wires. The model regression by the Napierian logarithm equation well represents the degradation trend of BFRP tendons under different levels of prestressing.

Creep behavior of basalt fiber reinforced polymer tendons for prestressing application

This paper investigates the creep behavior of newly developed basalt fiber reinforced polymer (BFRP) tendons for prestressing application. The creep strain to time relationship, creep rate and residual strength were experimentally studied and the relevant mechanism was elaborated. Furthermore, the creep rupture stress was predicted based on statistical analysis. The results show that the creep strain to time relationship of BFRP tendons depends highly on the stress level applied. The creep rate of BFRP tendons under low levels of stress remains in low and steady values. Meanwhile, the residual strength of BFRP after 1000h of sustained load still reaches approximately 95% of its initial tensile strength and the corresponding coefficient of variation (CV) is much less than the original CV. For prestressing application, the creep rupture stress limit for BFRP tendons can be adopted up to 52% of its tensile strength according to the reliability based analysis.