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Sun Z.,Nanjing Southeast University | Wu G.,Nanjing Southeast University | Wu Z.,Nanjing Southeast University | Zhang M.,Beijing Texida Technology Research and Development Co.
Tumu Gongcheng Xuebao/China Civil Engineering Journal | Year: 2011

The seismic performance of concrete columns reinforced by Steel-FRP (Fiber Reinforced Polymer) Composite Bar (SFCB) is quite different from that of ordinary RC (Reinforced Concrete) columns. Horizontal cyclic loading tests were conducted on concrete columns reinforced by SFCB and ordinary steel bars, separately, with an axial compression ratio of 0.12. Fiber types (basalt and carbon fibers) and steel/fiber ratio of SFCB were the main variable parameters. Test results showed that: (1) compared with ordinary RC column, concrete columns reinforced by SFCB had stable post-yield stiffness, and the load could increase significantly after the yielding of SFCB inner steel bar; (2) due to the post-yield stiffness of SFCB, SFCB reinforced concrete column had less column base curvature demand than ordinary RC column at the same column cap lateral deformation level, and therefore smaller unloading residual deformation could be achieved; (3) the outer FRP type of SFCB significantly influenced the performance of SFCB reinforced concrete columns, and steel-BFRP (basalt FRP) composite bar reinforced concrete columns had better ductility (longer effective length of post-yield stiffness) and smaller unloading residual deformation than steel-CFRP (carbon FRP) composite bar columns under the same unloading displacement.

Shen S.,Nanjing Southeast University | Wu Z.,Nanjing Southeast University | Yang C.,Nanjing Southeast University | Tang Y.,Nanjing Southeast University | And 2 more authors.
Tumu Gongcheng Xuebao/China Civil Engineering Journal | Year: 2010

Deformation is in general the most effective indicator of unforeseen damage accumulation, though it is difficult to acquire deformation distribution using traditional "point" monitoring methods. Based on the distributed optical fiber sensing technique of pulse-prepump Brillouin Optical Time Domain Analysis (PPP-BOTDA), an improved conjugated beam method is presented for monitoring the deformation distribution of simply-supported structures and continuous structures. This method is suitable for the combined action of loads and support settlements, extending the application of the traditional conjugated beam method. Another advantage of this method is that the relationship between structural deformation and strain is linear and all calculation parameters can be easily determined without using load or section stiffness. Theoretical and experimental investigations confirm that using this method, the accuracy of deformation monitoring in one span of structure is only related to the accuracy of strain measurements in this span, a characteristics useful for avoiding the influence from strain measurement errors in other spans.

Wu G.,Nanjing Southeast University | Yang Y.,Nanjing Southeast University | Yang Q.,CR17BG Construction Engineering Co. | Jiang J.,Beijing Texida Technology Research and Development Co. | Wu Z.,Nanjing Southeast University
Tumu Gongcheng Xuebao/China Civil Engineering Journal | Year: 2014

Steel reinforcements in traditional ballastless track slabs may influence the insulation performance of slabs, exacerbate the track circuit parameters, and in addition the use of insulation sleeves may also impair the bonding performance between the steel bar and concrete. A new type of ballastless track slab reinforced by steel-FRP composite bar (SFCB), which possesses excellent insulation performance, good bonding performance and high elastic modulus, etc, is thus proposed in this study. Insulation performance test of SFCB for ballastless track slab is conducted, and the results show that the rail parameters can be significantly improved. Based on the achieved desirable insulation performance, the experimental study on flexural behavior of SFCB slab is consequently conducted, and results show that SFCB slab has higher ultimate strength, higher energy reserve, and considerably higher displacement ductility than reinforced concrete (RC) slab. The results also show that after the yielding of steel bars, the crack development in SFCB slab may be restrained by the secondary stiffness of SFCB slab. Hence, the proposed SFCB reinforced ballastless track slab is appealing due to its good overall performance, which makes it desirable in engineering practice.

Yang Y.,Nanjing Southeast University | Wu G.,Nanjing Southeast University | Wu Z.-S.,Nanjing Southeast University | Jiang J.-B.,Beijing Texida Technology Research and Development Co. | Wang X.-B.,CR17BG Construction Engineering Co.
Composites Part B: Engineering | Year: 2015

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. © 2014 Elsevier Ltd. All rights reserved.

Sun Z.,Nanjing Southeast University | Wu G.,Nanjing Southeast University | Wu Z.,Nanjing Southeast University | Zhang M.,Beijing Texida Technology Research and Development Co.
Tumu Gongcheng Xuebao/China Civil Engineering Journal | Year: 2012

Though simulation of the mechanical properties of steel-FRP (fiber reinforced polymer) composite bar (SFCB) with OpenSees, the influences of reinforcement ratio, axial compression ratio, and SFCB post-yield stiffness ratio on the bearing capacity and deformation capacity of SFCB columns, and the maximum and residual deformation responses of SFCB column with different post-yield stiffness ratios under the excitation of three different earthquake waves were studied. The hysterisis behavior of SFCB columns and that of one reference RC (reinforced concrete) column were compared. The results showed: (1) the mechanical properties of SFCB under tensile and cyclic tensile loads could be well simulated by OpenSees based on the mixture rule, during which the steel bar and FRP were modeled separately; (2) with the same reinforcement ratio, the post-yield stiffness and corresponding deformation capacity of SFCB column increased with the increase of FRP content in SFCB; (3) the increase of column axial compression ratio had a negative effect on the post-yield stiffness of SFCB column, and more FRP in SFCB could delay the collapse of SFCB columns caused by the P-δ effect; (4) under the excitation of sever earthquakes of 400 Gal acceleration, SFCB column would exhibit smaller residual displacement than ordinary RC column when the post-yield stiffness ratio of SFCB was larger than 0.15; (5) both the calculation and the experimental results of SFCB columns under horizontal cyclic loading indicated that SFCB column could have smaller residual displacement than RC column, meaning that SFCB column had better post-earthquake reparability.

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