Calculation Methods For Bond And Beam Flexure Of Rebarsteel Fibre&Nanosized Materials Reinforced Concrete

With the further development of the constructions for water conservancy and hydropower engineering,ocean and coastal engineering,civil engineering as well as road and bridge engineering,the advanced concrete materials and structures with high performance are increasingly needed.Concrete compositing is an effective approach to improve the structural performance and meet the demands of modern constructions.In this study,a new type of concrete material is composited with steel fibres in meso scale and nanosized materials in micro scale,and is named as steel fibre and nanosized materials reinforced concrete?SFNMRC?.The bond behaviour of rebar embedded in SFNMRC and the flexural behaviour of SFNMRC beams were investigated.Moreover,the relevant calculation models and formulas were proposed.The main contents in this thesis are presented as follows:?1?The bond test of 164 specimens was conducted to investigate the effects of concrete strength,volume fraction of the steel fibre,amount of nanosized materials?Nano-SiO₂ and Nano-CaCO₃?,type of rebar as well as bonding specimen on the failure mode,bond stress-slip curve and bond strength.Afterwards,the action mechanisms of steel fibres and nanosized materials were analysed.?2?Based on the properties of large deformation and crack propagation for the SFNMRC,the expressions of hoop strain and hoop elongation for SFNMRC were developed.Furthermore,the calculation method to predict the bond strength of rebar embedded in the SFNMRC was proposed by using elasticity theory,fictitious crack theory and post-cracking softening model.This method was verified by the test results and was used to analyse the effects of the thickness of cover,number of cracks and diameter of rebar on the bond strength.?3?During the local bond stress-slip test,the strain gauges were attached to the inside of rebar uniformly with longitudinal slot.According to the measured strains,the distribution function of bond stress performed in cubic smooth spline was established.The distribution of bond stress and relative bond slip in bonded segment was obtained under the action of load at each stage.Finally,the bond stress-slip constitutive model reflecting the interaction process of rebar and SFNMRC was proposed.?4?The flexural test of 12 SFNMRC beams was conducted to investigate the effects of concrete strength,volumn fraction of steel fibre and amount of nanosized materials?Nano-SiO₂ and Nano-CaCO₃?on the cracking moment,crack propagation,concrete strains and deflection of mid-span section.With consideration of the enhanced effect of steel fibre on the cracked section of beams,the calculation method and formulas for the flexural capacity of SFNMRC beam were proposed.Moreover,by following the current national and international standards,the section stiffness of SFNMRC beams was predicted based on the effective moment of inertia method and analytical method.