Behaviour of plain and steel-fibre-reinforced high-strength concrete under uniaxial and biaxial compression

The purpose of this study was to investigate the mechanical characteristics of plain and steel-fibre-reinforced high-strength concrete under uniaxial and biaxial loading conditions. A number of plain and steel-fibre-reinforced high-strength concrete cubes having 28 days compressive strength of 82·7 MPa (12 000 psi) were made and tested. Four principal compression ratios (σ₂/σ₁ = 0·00, 0·50, 0·75 and 1·00), and four fibre concentrations (V_f = 0·0, 0·5, 1·0 and 1·5%) were selected as major test variables. From the test results, it was found that confinement stress in the minor stress direction has a pronounced effect on the strength and deformational behaviour and both the stiffness and ultimate strength of the plain and steel-fibre-reinforced high-strength concrete increased. The maximum increase of ultimate strength occurred at a biaxial stress ratio of 0·5 (σ₂/σ₁ = 0·5) in the plain high-strength concrete and the value recorded was 30% over the strength under the uniaxial condition. The failure modes of plain high-strength concrete under uniaxial compression were shown as splitting type but steel fibre concrete specimens under the biaxial condition showed a shear-type failure. The values of elastic modulus were also examined and found to be higher than those from the ACI and CEB expressions under the biaxial compression condition.