Abstract: In this research, dynamic cyclic loading and unloading tests at strain rate of 10^-4s^-1 under different unidirectional constant pressures are conducted on a large multi-functional static and dynamic force triaxial apparatus. Constant lateral pressures are 0%, 5%, 10% of the static uniaxial compressive strength. On this basis, the variation of hysteresis loop of stress-strain curve of concrete under cyclic loading and unloading with varying stress level is researched. The relation between dispersion hysteresis loop and energy dissipation is analyzed, and the damage estimation model is built. Furthermore, the damage characteristics of concrete are researched based on energy dissipation statistics. The following conclusions are obtained: 1) in initial unloading stage, the stress decreases rapidly and deformation recovers slowly, but the speed of recovery begins to accelerate with stress declining; 2) dissipative energy significantly increases with the increase of lateral stress under the same number of cycles, indicating that unit dissipated energy is apparently sensitive to lateral stress; 3) the damage estimation model of concrete is verified to perform well in fitting the relationship between damage and cumulative residue strain; 4) the development of damage decreases gradually with the increase of lateral pressure ratio, and in addition, the path of damage accumulation is greatly extended.

Key words: concrete, hysteresis loop, lateral pressure ratio, energy dissipation, damage estimation model, damage evolution