True-triaxial compressive behaviour of concrete under passive confinement

With the new triaxial testing system developed to generate passive confinement, 117 normal-weight concrete cubes were tested under 13 loading schemes, including biaxial compression and triaxial compression with both uniform and non-uniform passive confinement. The distinct failure patterns were observed under different monotonic loading schemes. The characteristics of peak strength and corresponding axial strain were investigated and compared with data for concrete under traditional triaxial testing. The peak strength and corresponding axial strain have been observed to be related to the confinement stiffness, non-uniform stiffness ratio and the maximum lateral strain. On comparison, it revealed that the models calibrated from the traditional triaxial testing could predict the peak strength with an error within ±10% but cannot well predict the corresponding axial strain.