Behaviour and performance of structural members with steel fibre reinforced concrete
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Date
2019
Authors
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Publisher
Universiti Teknologi Malaysia
Abstract
Steel fibre reinforced concrete (SFRC) is seen to have the ability to improve the bond strength of steel reinforcing bars due to confinement effect from the steel fibres and concrete. However, this confinement effect has not been examined thoroughly yet. Therefore, experimental works were carried out to investigate the effects of steel fibres in influencing the bond behaviour between deformed steel bars and SFRC. The experimental works were carried out in three phases. In Phase 1, the SFRC mechanical properties of compressive strength, splitting tensile strength, flexural strength and fracture energy, with different steel fibre contents of 0%, 0.25%, 0.5%, 0.75%, 1.0%, 1.25%, 1.5% and 1.75% were investigated. In Phase 2, forty-eight pullout tests were conducted using Grade 40 SFRC with variable amount of steel fibres similar to the amount used in Phase 1. High yield deformed steel bars of 16 mm and 20 mm diameters were used as embedded reinforcement bars in the pullout specimens. The pullout specimens were subjected to increasing axial pullout load and the responses of load-slip were recorded. In Phase 3, SFRC with the optimum 1.25% fibre content obtained from the finding of Phase 2 combined with steel tie bars was used as the connections between beams and columns of a precast concrete sub-frame. For comparison, two other precast concrete sub-frames were constructed using connections comprising cast in-situ normal concrete only and cast in-situ normal concrete with steel tie bars respectively. All the three precast concrete sub-frames were tested for progressive collapse. The test results of Phase 1 showed that the SFRC demonstrated a significant improvement in the splitting tensile strength, flexural strength and fracture energy, except for compressive strength, which indicated a little enhancement. The behaviour of SFRC under tension was significantly promising in providing high concrete deformation due to the steel fibre bridging effect against the crack. Meanwhile, results of Phase 2 showed that the use of steel fibres enhanced the bond strength between steel bars and SFRC by providing passive confinement that delays the propagation of radial cracks in the surrounding SFRC concrete. The SFRC with 1.25% steel fibre content was able to provide the optimum performance in terms of workability, bond strength and splitting tensile strength. Meanwhile, the SFRC with 1.5% and 1.75% steel fibre contents had low workability and showed less improvement in the increment of bond and splitting tensile strength. Furthermore, higher bond strength was observed in smaller diameter reinforcement bar as compared to the larger reinforcement bar diameter. The test results of Phase 3 showed that the use of cast-in-situ SFRC with 1.25% steel fibre content in the connections of the precast concrete sub-frame had produced a satisfactory progressive collapse performance of the sub-frame through catenary action where the deflection of the precast beam under column loss scenario was delayed up to 55 minutes. Therefore, in order to provide an effective catenary tie in precast concrete beam-column connection, it is recommended to use cast-in-situ SFRC with 1.25% steel fibre content.
Description
Thesis (PhD. (Civil Engineering))
Keywords
Fiber-reinforced concrete, Reinforcing bars—Testing