Shear strength and failure criterion analysis of steel fiber reinforced concrete exposed to elevated temperature under combined compression–shear loading

Adding steel fiber to concrete preparation to enhance residual strength and ductility is a potential solution to improve reliability of specific concrete members with compression–shear loading zones, such as deep beams, trusses and column joints, after exposure to high temperature. In this study, the primary aim is to explore the impact of steel fibers on concrete behaviors in shear failure under various exposure temperatures and normal stress. Compression–shear performance of steel fiber reinforced concrete was tested under several conditions of volume fraction of steel fibers (V_sf = 0, 1.0%, 1.5%, and 2.0%), exposure temperature (T = 20 °C, 200 °C, 400 °C, and 600 °C), and normal stress ratios (k = 0, 0.2, 0.4, 0.6, and 0.8), and compression–shear failure patterns and load–shear displacement curves were investigated. The results demonstrate that incorporation of steel fibers enhance ductile behavior of specimen under compression–shear loading, with a higher presence of friction traces and jagged edges appearing at shear interface. After temperature treatment above 400℃, the characteristics of tensile failure gradually disappear, while more crushed failure occurs. The peak shear strengths decrease significantly with the increase of exposure temperature. For different volume fraction of steel fibers (1.0%, 1.5%, and 2.0%), the shear strengths at 400 °C increase by 12.5%, 15.9%, and 11.1%, respectively. The optimal compression–shear strengthening effect is V_sf = 1.5%. Finally, according to the experimental results, the equivalent strength τ_oct − σ_oct theoretical calculation model is determined to be the most suitable compression–shear strength prediction of SFRC at various temperatures.