Experimental Study On Dynamic Loading Of Concrete Under Fatigue Loads And Freeze-thaw Cycles

In cold areas at high latitudes,structures such as concrete dams,bridges,and tunnels will experience the combined effects of fatigue loads and freeze-thaw cycles.In practice,concrete is often subjected to dynamic loading on this basis.In this paper,210 concrete test blocks are taken as the research object.The dynamic performance of concrete under the single factor of freeze-thaw cycles and fatigue loading and the dynamic characteristics of concrete after double-factor effects of freeze-thaw fatigue are studied.The main results are as follows:1.The dynamic characteristics of concrete under single-factor fatigue loading are studied.The effects of the number of fatigue times and strain rate on the performance of the concrete are studied by measuring the ultrasonic velocity and the uniaxial compression test,and the mechanism of concrete's relative dynamic elastic modulus,compressive strength and effective stress area changing with the change of the number of fatigue times and strain rate.The study found that concrete fatigue damage is a gradual accumulation process.Significant "rate" effect on concrete test blocks after fatigue,and the "rate" sensitivity of the test block affected by the number of fatigue effects.2.The dynamic characteristics of concrete under single-factor freeze-thaw cycles were studied.The effects of freezing and thawing times and strain rate on concrete performance were studied by freeze-thaw concrete test block quality,ultrasonic velocity,and uniaxial compressive strength.Analyze the change law of concrete mass loss rate and relative dynamic elastic modulus,and study the change mechanism of compressive strength and effective load area with the number of freeze-thaw cycles and strain rate.The study found that changes in the number of freeze-thaw cycles and the strain rate will have a great impact on the failure state of the concrete.As the number of freeze-thaw cycles increases,the mass of the test block first increases and then decreases.The relative dynamic elastic modulus loss mainly occurs in the early freeze-thaw cycles.The number of freeze-thaw cycles affects the "rate" sensitivity of concrete,and puts forward design suggestions for concrete structures under dynamic conditions based on actual conditions.3.Study the dynamic characteristics of concrete after first fatigue loading and thenfreezing-thawing cycle.The uniaxial compression fatigue test is performed first,and then the freeze-thaw cycle test is performed,during which the wave velocity of the concrete test block is measured according to the test plan,and the uniaxial compression test is performed.The results show that the damage caused by fatigue loading and freeze-thaw cycles is higher than the superposition of single factor damage.Analyzes the dynamic compressive failure mechanism of concrete under first fatigue loading and then freezing-thawing cycle and the "rate" correlation of compressive strength of concrete,and the change mechanism and significance of the trend of relative dynamic elastic modulus full-time history and stress-strain curve are analyzed.Regression fits the full stress-strain curve.4.Study the dynamic characteristics of concrete after first freezing-thawing cycle and then fatigue loading.The freeze-thaw cycle test is performed first and then the uniaxial compression fatigue test is performed.During which the wave velocity of the concrete test block is measured according to the test plan,and the uniaxial compression test is performed.The research results show that the order of freeze-thaw and fatigue affects the performance of concrete,and the damage degree of concrete after first freezing-thawing cycle and then fatigue loading is smaller than that of concrete after first fatigue loading and then freezing-thawing cycle.The correlation between the relative dynamic elastic modulus full-time history curve and the "rate" of the compressive strength of the concrete is analyzed.Finally,the effects of changes in freezing and thawing times,fatigue times,and strain rates on the stress-strain curve are analyzed.