双轴拉压混凝土在冻融循环后的力学性能及破坏准则

北方寒冷地区的大多数混凝土结构物和水坝等处于复杂应力状态,冻融循环对混凝土的力学性能产生不利影响。利用大连理工大学海岸和近海工程国家重点试验室的大型混凝土静、动三轴试验系统,对经过0,25,50,75次冻融循环的混凝土,进行了0,-0.05,-0.15,-0.25共4种比例加载路径的双轴拉压试验,测得了混凝土的抗压强度和抗拉强度,及2个加载方向的应变,并根据试验结果,系统地探讨了冻融循环后,混凝土在不同拉压比下的双轴拉压强度和变形特性,发现随冻融循环次数的增加,混凝土的抗压强度、抗拉强度明显降低,拉压比对冻融循环后混凝土强度和变形性能有明显的影响。在主应力空间和八面体应力空间建立了同时考虑冻融循环次数和拉压比的冻融循环后混凝土双轴拉压的破坏准则,与试验值符合较好。经分析得出结论,实际工程中,处于双轴拉压应力状态的混凝土结构的抗冻融循环能力低于单轴应力状态的混凝土结构,因此,设计时要引起足够的重视。

MECHANICAL PROPERTY AND FAILURE CRITERION OF CONCRETE UNDER BIAXIAL TENSION AND COMPRESSION AFTER FREEZE-THAW CYCLING

Most concrete structure buildings and dams in northern cold region are in complex stress state,and the freeze-thaw cycling has adverse effect on the mechanical properties of concrete. Biaxial concrete tension- compression tests of 4 different stress ratios,0,-0.05,-0.15 and -0.25 after 0,25,50 and 75 freeze-thaw cycles are carried out respectively using the concrete static-dynamic triaxial test system in the State Key laboratory of Coastal and Offshore Engineering,Dalian University of Technology. The strain of two loading directions and the strength of concrete are measured. The strength and the deformation of concrete under different tension-compression stress ratios are studied based on the experiments;and the results indicate that the compressive strength and the tensile strength are decreased with the increasing of freeze-thaw cycles;and that the effect of tension-compression stress ratio on strength and deformation of concrete after freeze-thaw cycling is significant. Failure criterion of concrete under biaxial tension and compression is established in normal stress space and octahedral stress space. The results show that in practical cases,resistance capability against freeze-thaw cycling of concrete structure under biaxial tension and compression is inferior to that of concrete structure under uniaxial stress;and more attention should be paid to this point in structure design.