冻融循环与疲劳荷载作用下混凝土损伤研究

为研究冻融循环与轴向疲劳荷载作用下混凝土力学性能损伤演化规律,对混凝土试件分别进行冻融循环、疲劳加载、先冻融循环后疲劳加载和先疲劳加载后冻融循环4种损伤试验,以试件经历损伤后的抗压强度劣化作为损伤评价指标研究混凝土的损伤特性和机理,同时研究相对动弹性模量和质量的劣化规律。研究结果表明:不同联合作用下,混凝土的相对动弹性模量均呈现降低趋势。冻融循环单一因素作用下,混凝土强度随冻融次数的增加逐渐降低;疲劳荷载单一因素作用下,混凝土强度随疲劳次数增加呈先升后降的趋势,疲劳4万次时,混凝土的损伤度为1.8%;先冻融循环后疲劳加载作用下,即混凝土先受冻融循环作用,再受1万次应力水平(0.1 f_c~0.5 f_c)的疲劳荷载作用时,随疲劳次数的增加,试件的强度均呈现升高趋势;先疲劳加载后冻融循环作用下,随冻融次数的增加,混凝土的力学性能损伤显著,历史疲劳次数为0.5万次和1万次,再经历75次冻融循环作用时,其损伤度分别为19%和24.2%。研究成果可为建立符合实际工程的混凝土结构耐久性设计理论提供较可靠的基础依据。

Damage of Concrete under Freeze-thaw Cycles and Fatigue Load

Damage tests of concrete specimens were conducted to investigate into the damage evolution law of concrete's mechanical properties under the actions of freeze-thaw cycles and axial fatigue load.Cyclic freezing and thawing,fatigue loading,fatigue loading after freeze-thaw cycles and freeze-thaw cycles after fatigue loading were applied on concrete specimens respectively.With the deterioration of compressive strength as the damage assessment index,the deterioration of relative dynamic modulus of elasticity and mass were obtained.Results show that under combined actions,the relative dynamic elastic modulus of concrete decreases:1) under the single action of cyclic freezing and thawing,concrete strength declines gradually as freeze-thaw cycle proceeds;2) while under the single action of fatigue load,concrete strength grows firstly and then declines as the number of fatigue increases,with the damage degree equals 1.8％ when fatigue loading is imposed for 40 000 times;3) under the combined actions of fatigue loading (with a stress level 0.1 fc ～0.5fc for 10 000 times) after freeze-thaw cycles,concrete strength shows a trend of rising;4) while under the combined actions of cyclic freezing and thawing (for 75 times) after fatigue load (imposed for 5 000 times and 10 000 times respectively),the mechanical properties of concrete deteriorates remarkably as freeze-thaw cycle proceeds,with the damage degree equals to 19％ and 24.2％,respectively.This study provides reliable theoretical basis for the design theory of concrete structures consistent with practical engineering.