定侧压混凝土双轴等幅拉压疲劳性能试验研究

针对预应力混凝土桥梁在使用荷载下出现的双轴拉-压疲劳状态,通过自行改造的MTS试验机对定侧压下混凝土等幅拉-压疲劳性能进行了试验研究。在对试验结果进行分析的基础上,综合单轴拉-压疲劳的结论给出了该种疲劳状态下混凝土的S-N关系和双轴疲劳强度包络线。根据试验过程中实测的应力-应变数据分析了混凝土的变形性能,提出了疲劳总应变、第二阶段应变率及疲劳变形模量与疲劳寿命之间的关系式。研究结果表明:定侧压作用下混凝土拉-压疲劳破坏形态与侧压水平无关;侧压降低了混凝土拉-压疲劳强度,侧压水平越高其降低得越明显。

Experimental study of fatigue behavior of concrete under constant-amplitude biaxial cyclic tension-compression with constant confinement

The fatigue tests on biaxial tension-compression under constant-amplitude cyclic loading with constantly confined stress were carried out on plain concrete,simulating the fatigue state subjected frequently to pre-stressed concrete bridges with vehicle loads.A biaxial fatigue test equipment based on the stress-controller close-loop system of MTS is reconstructed.Then,the relationship of S-N and the fatigue strength envelopes of concrete under tension-compression loads with constant confinement are presented based on the analysis of the results of present experiments and fatigue tests under uniaxial tension-compression cyclic loading reported in the available literature.According to the data of stress and strain recorded in the process of fatigue tests,the deformation characteristics of concrete under the state of stress in present study are also investigated,which includes the development of longitudinal and transverse strains,the secondary creep rate and the deformation modulus of concrete in terms of cyclic number.The experimental results indicate that the lateral confinement stress level has little influnce on failure mode,but significant influence on fatigue strength of concrete.