定侧压混凝土双轴抗压疲劳变形特性试验研究

本文通过自行改造的MTS疲劳试验机对混凝土在定侧压下等幅和变幅抗压疲劳的变形性能进行了试验研究。根据试验实测的混凝土循环应力-应变数据,分析了混凝土双轴受压疲劳应变、刚度与超声波速的衰减规律,提出了与侧压水平相关的疲劳第二阶段应变率和混凝土疲劳寿命之间的关系式。根据试验得到的试件疲劳破坏形态分析了定侧压下混凝土双轴受压疲劳破坏的机理。试验结果表明:定侧压下混凝土受压疲劳破坏形态与侧压水平相关,而且疲劳应变发展仍符合三阶段规律,第二阶段应变率与疲劳寿命之间也具有很好的相关性。

Experimental investigation of deformation characteristics of concrete under cyclic biaxial compression with constant confined stress

An experimental research program was carried out with the aim of investigating the deformation characteristics of normal strength concrete under multistage cyclic biaxial compression with constant confined stress. A biaxial compressive test equipment based on the stress-controller close-loop system of MTS was reconstructed and used in the test. The results of fatigue tests were presented in the form of the diagrams of cyclic stress-strain curves which were recorded in the progress of tests. The deformation characteristics including the development of longitudinal and transverse fatigue strains, the secondary creep rate under the states of constant-amplitude and variable-amplitude cyclic compressive loads,and deformation modulus of concrete in terms of cyclic number, were drawn from the analysis of experimental results. In addition, An ultrasonic pulse velocity method was used to measure the damage growth during cyclic loading of concrete, and which results implied the progress of failure of concrete under biaxial cyclic compressive loads with constant confined stress. The microcosmic destructive mechanism of concrete under the present stress states was analyzed as well. The experimental results showed that the failure mode of compression fatigue of concrete was correlated with the magnitude of confined stress, while the development of fatigue strain conformed to the laws of three-stages. Furthermore, the rate of strain in second stage had also a perfect correlation with the fatigue life of concrete.