ABSTRACT
Basalt-fiber-reinforced plastic-bars-reinforced concrete beams (i.e., BFRP-RC beams) usually possess significant deformations compared to reinforced concrete beams due to the FRP bars having a lower Young's modulus. This paper investigates the effects of adding steel fibers into BFRP-RC beams to reduce their deflection. Ten BFRP-RC beams were prepared and tested to failure via four-point bending under cyclic loading. The experimental variables investigated include steel-fiber volume fraction and shape, BFRP reinforcement ratio, and concrete strength. The influences of steel fibers on ultimate moment capacity, service load moment, and deformation of the BFRP-RC beams were investigated. The results reveal that steel fibers significantly improved the ultimate moment capacity and service load moment of the BFRP-RC beams. The deflection and residual deflection of the BFRP-RC beams reinforced with 1.5% by volume steel fibers were 48.18% and 30.36% lower than their counterpart of the BFRP-RC beams without fibers. Under the same load, the deflection of the beams increased by 11% after the first stage of three loading and unloading cycles, while the deflection increased by only 8% after three unloading and reloading cycles in the second and third stages. Finally, a new analytical model for the deflection of the BFRP-RC beams with steel fibers under cyclic loading was established and validated by the experiment results from this study. The new model yielded better results than current models in the literature.
ABSTRACT
This research investigated the flexural behavior of high-strength concrete beams reinforced with continuous basalt fiber-reinforced polymer (BFRP) bars and discrete steel fibers. Five concrete beams with the dimensions of 150 × 300 × 2100 mm3 were constructed and tested to failure under four-point bending cyclic loading. The specimens consisted of four BFRP-reinforced concrete beams with various reinforcement ratios (ρf), namely, 0.56%, 0.77%, 1.15%, and 1.65%, and one conventional steel-reinforced concrete beam for comparison purposes. The cracking behavior, failure modes, load-deflection behavior, residual deformation, and stiffness degradation of the beams were studied. Additionally, a deformation-based approach was used to analyze the deformability of the beams. The results show that an increase in the ρf effectively restrained the crack widths, deflections, and residual deformation while also enhancing the flexural bearing capacity of the beams. In comparison to the first displacement cycle, the bearing capacity dropped by 10% on average in the third cycle. The stiffness exhibited a fast to slow degradation trend until failure. The residual stiffnesses were higher in beams with a higher ρf. The over-reinforced beams had superior deformability than the under-reinforced beams, according to the deformability factors.
ABSTRACT
The ductile behaviour of composite beams reinforced with glass fibre-reinforced polymer (GFRP) pultruded rectangular tubes was investigated in this paper. The composite beams were reinforced with GFRP tubes and different steel products, aiming to improve their ductility by using steel products. The main parameters were the types of the steel reinforcement, namely rebars and steel angles. The flexural behaviour of four beam specimens was tested by using a four-point bending test. The experimental results show that the yield load of the specimens was determined by the steel products and the ultimate load was controlled by the GFRP tubes. Two ductility methods (displacement ductility and energy ductility) were used to evaluate the change of the ductility. Both the methods confirmed that the ductility of the composite beam was improved in varying degrees by using rebars and steel angles. Moreover, the analysis shows that improving the yield load or decreasing the ultimate load of the composite beams contributed to the improvement of the ductility.
ABSTRACT
Steel fiber-reinforced concrete (SFRC) beams with fiber-reinforced polymer (FRP) bars are promising new composite structures. To investigate the durability of BFRP-SFRC beams, eleven beams were fabricated and conducted via four-point bending tests under cyclic loading. The experimental variables included BFRP reinforcement ratios, pre-cracked widths and environments (Natural or Seawater erosion). Experiment results revealed that the load-deflection curves of BFRP-SFRC beams showed bilinear growth. With the increase in loading and unloading cycles, the peak load and energy consumption of the tested beams decreased, and the impact of loading and unloading cycles on the flexural performances of the BFRP-SFRC beams enhanced with the increase in displacement. Under the same load, as the pre-crack width increases, the deflection of the BFRP-SFRC beam decreases. The deflection of the beam with a pre-crack width of 0.4 mm was 1.34 times than that of the beam without a pre-crack at the load of 100 kN. What is more, the pre-crack width had a bad effect on the energy consumed by the BFRP-SFRC beams. Compared with no pre-crack beam, the energy consumed by the beams with 0.02, 0.2 and 0.4 mm pre-crack width were decreased by 1.5%, 7.8% and 11.0% at the 18 mm displacement, respectively. Significantly, the effect of sea water erosion on the energy consumption of tested beams with high BFRP reinforcement ratios were smaller than that of tested beams with low BFRP reinforcement ratios. Finally, a calculation model of deformation of BFRP-SFRC beams under seawater erosion environments was proposed based on the effective moment of inertia methods. Compared with the existing calculation methods, this model was better correlated with the experimental results.
ABSTRACT
The behavior of steel fiber concrete, which is the most widely used building material, has been widely examined. However, methods for calculating Fracture parameters differ by fracture behavior of SFHSC with different strengths. In this study, the fracture behavior of steel-fiber-reinforced high-strength concrete (SFHSC) was -investigated using three-point bending tests. A total of 144 notched concrete beams with a size of 100 mm × 100 mm × 515 mm were tested for three-point bending in 26 groups. The effects of the steel fiber volume ratio, steel fiber type, and relative notch depth on the fracture toughness (KIC) and fracture energy (GF) of SFHSC specimens were studied. The results show that an increase in the volume fraction of steel fiber (ρf) added to high-strength concrete (HSC) significantly improves the fracture behavior of HSC. As compared to milled and sheared corrugated steel fibers, cut bow steel fibers significantly improve the fracture behavior of SFHSC. The effect of incision depth changes on the KIC and GF of SFHSC and HSC for the comparison group has no common characteristics. With an increase in incision depth, the values of KIC of the SFHSC specimens decrease slightly. The GF0.5/GF0.4 of the SFHSC specimens show a decreasing trend with an increase in ρf. According to the test results, we propose calculation models for the fracture behavior of SFHSC with different strengths. Thus, we present a convenient and accurate method to calculate fracture parameters, which lays a foundation for subsequent research.
ABSTRACT
Pervious concrete is considered to be porous concrete because of its pore structure and excellent permeability. In general, larger porosity will increase the permeability coefficient, but will significantly decrease the compressive strength. The effects of water-cement ratio, fiber types, and fiber content on the permeability coefficient, porosity, compressive strength, and flexural strength were investigated. The pore tortuosity of the pervious concrete was determined by volumetric analysis and two-dimensional cross-sectional image analysis. The concept and calculation method of porosity tortuosity were further proposed. Results show that the permeability coefficient of the pervious concrete is the most suitable with a water-cement ratio of 0.30; the water permeability of the pervious concrete is influenced by fiber diameter. The permeability coefficient of pervious concrete with polypropylene thick fiber (PPTF) is greater than that with copper coated steel fiber (CCF) and the polypropylene fiber (PPF). The permeability coefficient is related to tortuosity and porosity, but when porosity is the same, the permeability coefficient may be different. Finally, general relations between the permeability coefficient and porosity tortuosity are constructed.
