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Shi J.,Nanjing Southeast University | Wang X.,Nanjing Southeast University | Wu Z.,Nanjing Southeast University | Zhu Z.,Jiangsu Green Materials Valley New Material T and D Co.
Journal of Reinforced Plastics and Composites | Year: 2015

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. © 2015 SAGE Publications.


Shi J.,Nanjing Southeast University | Wang X.,Nanjing Southeast University | Wu Z.,Nanjing Southeast University | Zhu Z.,Jiangsu Green Materials Valley New Material TandD Co.
Construction and Building Materials | Year: 2015

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 1000 h, 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. © 2015 Elsevier Ltd.


Wang X.,Nanjing Southeast University | Zhao X.,Nanjing Southeast University | Wu Z.,Nanjing Southeast University | Zhu Z.,Jiangsu Green Materials Valley New Material T and D Co. | Wang Z.,Nanjing Southeast University
Journal of Composite Materials | Year: 2016

This paper focuses on the interlaminar shear behavior of basalt fiber reinforced polymer (FRP) laminates impregnated with epoxy and vinyl ester resins as well as hybrid basalt and carbon FRP laminates. Meanwhile, the interlaminar shear behavior of carbon and E-glass FRP laminates was also studied for comparison. The experiments were conducted according to the ASTM-D-2344 standard, and the failure modes, load-deformation (L-D) relationships, and interlaminar shear stress to normalized deformation relationships of various FRP laminates were analyzed. The differences in interlaminar shear behavior among different fibers and resins were identified. The fracture surfaces of the laminate specimens with different fibers were examined by scanning electron microscopy. Furthermore, the hybrid effect on interlaminar shear behavior was discussed and the interlaminar shear strength was predicted based on above analysis. The results show that the L-D relationships of FRP laminates can be classified into three types, which are determined by the interlaminar shear strength between fiber layers and the resin as well as by the failure modes. The interlaminar shear strength of basalt FRP with vinyl ester resin is higher than that of the glass FRP but less than that of the carbon FRP. The adoption of epoxy resin and the hybridization of basalt and carbon fibers can enhance the interlaminar shear strength of basalt FRP. In addition, the scanning electron microscopy images of fracture surfaces of the laminate specimens confirm the differences of interlaminar behavior of various composites. The hybrid effect on the interlaminar shear behavior is reflected in the integration of both advantages of basalt FRP and carbon FRP in the interlaminar shear stress to nominal deformation relationship, which results in both higher interlaminar shear strength at the cracking and the final stages. Finally, the interlaminar shear strength of different FRP laminates can be accurately predicted by the proposed model. © The Author(s) 2015.


Wang X.,Nanjing Southeast University | Shi J.,Nanjing Southeast University | Wu Z.,Nanjing Southeast University | Zhu Z.,Jiangsu Green Materials Valley New Material T and D Co.
Journal of Composites for Construction | Year: 2016

This 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 tendons can sustain 2 million cyclic loadings under a stress range of 0.05fu (85 MPa) and maximum stress of 0.6fu (1,018 MPa). Furthermore, the elastic modulus of BFRP tendons before failure remains constant regardless of the number of cycles. Prediction of fatigue strength (limit of stress range and maximum stress to sustain 2 million cyclic loadings) based on experimental fitting shows a satisfactory consistency with the previously mentioned experimental results (0.05 and 0.6fu). A recommendation of a stress range of 0.04fu (68 MPa) and maximum stress of 0.53fu (899 MPa) are proposed with 95% reliability for BFRP tendons in prestressing applications. © 2015 American Society of Civil Engineers.


Wang X.,Nanjing Southeast University | Shi J.,Nanjing Southeast University | Wu Z.,Nanjing Southeast University | Zhu Z.,Jiangsu Green Materials Valley New Material T and D Co.
Materials and Design | Year: 2016

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. © 2015 Elsevier Ltd.


Zhao X.,Nanjing Southeast University | Wang X.,Nanjing Southeast University | Wu Z.,Nanjing Southeast University | Zhu Z.,Jiangsu Green Materials Valley New Material TandD Co.
International Journal of Fatigue | Year: 2016

This paper studies the fatigue behavior of basalt fiber reinforced epoxy polymer (BFRP) composites and reveals the degradation mechanism of BFRP under different stress levels of cyclic loadings. The BFRP composites were tested under tension-tension fatigue load with different stress levels by an advanced fatigue loading equipment combined with in-situ scanning electron microscopy (SEM). The specimens were under long-term cyclic loads up to 1 × 107 cycles. The stiffness degradation, S-N curves and the residual strength of run-out specimens were recorded during the test. The fatigue strength was predicted with the testing results using reliability methods. Meanwhile, the damage propagation and fracture surface of all specimens were observed and tracked during fatigue loading by an in-situ SEM, based on which damage mechanism under different stress levels was studied. The results show the prediction of fatigue strength by fitting S-N data up to 2 × 106 cycles is lower than that of the data by 1 × 107 cycles. It reveals the fatigue strength perdition is highly associated with the long-term run-out cycles and traditional two million run-out cycles cannot accurately predict fatigue behavior. The SEM images reveal that under high level of stress, the critical fiber breaking failure is the dominant damage, while the matrix cracking and interfacial debonding are main damage patterns at the low and middle fatigue stress level for BFRP. Based on the above fatigue behavior and damage pattern, a three stage fracture mechanism model under fatigue loading is developed. © 2016 Elsevier Ltd. All rights reserved.

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