不同侧应力状态下混凝土循环加卸载损伤特性

Dynamic Damage Properties of Concrete Subjected to Cyclic Loading and Unloading with Different Lateral Stresses

采用大型多功能液压伺服静动力三轴仪对不同单向恒定侧压下的混凝土进行应变速率为10-4s-1的等应变增量循环加卸载试验,恒定侧压为单轴静态抗压强度的0%,5%,10%。研究了不同侧应力水平下应力-应变全曲线中滞回环的变化规律,分析滞回环与耗散能的关系,并构建损伤估计模型,最后基于耗散能统计,研究混凝土的损伤特性。得出主要结论如下:(1)全曲线中滞回环在卸载初始阶段应力下降较快而变形恢复很慢,但随着应力的逐渐下降,应变恢复才开始加快;(2)在循环次数相同时,耗散能随着侧应力的增加而增加,且增加幅度明显,表明单位耗散能具有明显的侧应力敏感性;(3)建立的双参数损伤估计模型,能够很好地拟合循环加卸载损伤与累积残余应变的关系;(4)随着侧压比的提高,混凝土损伤发展速度逐渐减慢,损伤累积的路径大幅延长。

In this research,dynamic cyclic loading and unloading tests at strain rate of 10-4 s-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.