Failure Mode and Constitutive Model of Plain High-Strength High-Performance Concrete under Biaxial Compression after Exposure to High Temperatures

ABSTRACT An orthotropic constitutive relationship with temperature parameters for plain high- strength high-performance concrete (HSHPC) under biaxial compression is developed. It is based on the experiments performed for characterizing the strength and deformation behavior at two strength levels of HSHPC at 7 different stress ratios including α = σ2 : σ3 = 0.00 : −1, −0.20 : −1, −0.30 : −1, −0.40 : −1, −0.50 : −1, −0.75 : −1, −1.00 : −1, after the exposure to normal and high temperatures of 20, 200, 300, 400, 500 and 600°C, and using a large static-dynamic true triaxial machine. The biaxial tests were performed on 100 mm × 100 mm × 100 mm cubic specimens, and friction-reducing pads were used consisting of three layers of plastic membrane with glycerine in-between for the compressive loading plane. Based on the experimental results, failure modes of HSHPC specimens were described. The principal static compressive strengths, strains at the peak stress and stress-strain curves were measured; and the inuence of the temperature and stress ratios on them was also analyzed. The experimental results showed that the uniaxial compressive strength of plain HSHPC after exposure to high temperatures does not decrease dramatically with the increase of temperature. The ratio of the biaxial to its uniaxial compressive strength depends on the stress ratios and brittleness-stiffness of HSHPC after exposure to different temperature levels. Comparison of the stress-strain results obtained from the theoretical model and the experimental data indicates good agreement.