基于残余应变的多侧压下混凝土受拉疲劳损伤研究
DAMAGE STUDY ON CONCRETE FATIGUE IN TENSION UNDER MULTI-LATERAL PRESSURES BASED ON RESIDUAL STRAINS
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摘要: 在侧压分别为0.25fc和0.50fc及其组合条件下,进行了混凝土在多侧压下的受拉等幅与变幅疲劳试验,得到了疲劳累积极限应变和残余极限应变,建立了残余应变与疲劳次数关系方程,并给出了残余应变与循环次数关系曲线。根据残余应变的稳定性,也即不受加载历程的影响,主要与侧应力水平和相对疲劳次数有关,以残余应变与相应应力水平下的残余极限应变之比作为损伤变量,建立了损伤变量与疲劳次数关系的统一方程,并给出了损伤变量与疲劳次数关系曲线。同时,对单轴、单、双侧压下的混凝土受拉疲劳的累积极限应变和残余极限应变与相应应力条件下的静态峰值应变进行了比较,其结果是随着侧应力水平的增加,相应的极限应变增加,再次说明了侧应力水平的影响。静态峰值应变与相应条件下的疲劳累积极限应变接近,残余极限应变与静态峰值应变及疲劳累积极限应变的比值较为稳定,其变化区间在0.22~0.28之间,且两种比值之间相差0.0~0.2。最后,对Miner准则进行了改进,并根据所建立的损伤模型与改进的Miner准则,对变幅疲劳寿命进行了预测,其结果是较为合理的。Abstract: The tensile fatigue experiments of concrete for constant and variable amplitudes under multi-lateral pressures of 0.25fc, 0.50fc and their combination, respectively were conducted. The cumulative ultimate strain, the ultimate residual fatigue strain, and the relationships between the residual strains and the number of cycles were obtained. It is found that the residual strain was independent of loading history, and was mainly affected by lateral stress levels and the ratio of cycles. A united equation between damage variable and the cycle ratio was developed based on the damage variable defined as the ratio of residual strain to that of ultimate one. Therefore, the ratio values of cumulative strains and the static peak ones under the same stress level were compared with that of ultimate residual strains. It is shown that the ultimate strain increased with lateral stress accordingly; the influences of lateral stress level on ultimate stains were proved; on the other hand, the static peak strains approached the ultimate cumulative fatigue strain. The ratio values between the ultimate residual fatigue strain, the static peak strain and the ultimate cumulative strain of fatigue were stable. The variation range is from 0.22 to 0.28, and the deviation of the two ratios is 0.0 to 0.2. In the end, the variable amplitude fatigue lives were predicted by the modified Miner rule and the proposed damage models, the results were suitable.