Study On The Effect Of Fatigue Damage On The Dynamic Compression Performance Of Concrete

Most of the concrete structures in the urban lifeline system will encounter dynamic loads such as earthquake loads,wind loads,impacts,and hydrodynamic pressure during their work.At the same time,they also bears the fatigue load caused by vehicle traffic and equipment vibration.For example,the airport runway has to withstand the fatigue load brought by the taxiing of the aircraft,and also resist the impact load when the aircraft lands.However,the current academic research in the field of dynamic properties of concrete materials is based on materials with no initial fatigue damage,and doesn’t consider the fatigue damage and performance degradation caused by longterm repeated loads during the actual service of concrete.If the existing research results on the dynamic properties of concrete materials are directly applied to existing service structures,their dynamic properties may be seriously overestimated.In addition,the compressive resistance of concrete materials is one of its most important mechanical properties.Therefore,this paper studies the dynamic compressive properties of concrete under fatigue damage based on a large number of test results,including the following contents:(1)The uniaxial compression-compression fatigue test of concrete material was carried out.Applying a specified number cyclic loads to the concrete material which simulates the fatigue state of the actual concrete service structure,it can achieve different degrees of fatigue damage.CT scan and residual strength test were carried out on concrete specimens under different damage conditions,and parameters such as defect volume ratio,residual strength,residual secant modulus,and ultrasonic velocity were obtained under different damages.Among them,the defect volume ratio increased with the increase of fatigue damage degree.The other parameters decrease with the increase of fatigue damage degree.From the perspective of crack development,the reasons for the attenuation of various properties such as strength and stiffness of concrete under fatigue load are explained that can be called the fatigue damage mechanism.(2)Based on the mesoscopic and macroscopic test results,the fatigue damage development curve based on various properties is drawn and analyzed.The most economical and effective method for quantifying fatigue damage is average ultrasonic wave.In addition,this paper proposes an ideal transformation formula for ultrasonic detection of fatigue damage.(3)The dynamic impact compression test was carried out on the concrete specimen using the drop hammer impact device.The failure mode,impact force and strain time history curve of the specimen under different fatigue damage degrees and different impact heights were obtained after the inertia force correction.Based on the test results,the variation law of stress peak value,strain peak value,strain rate and dynamic increase factor of concrete specimens under different impact conditions was compared and analyzed.The higher the strain rate,the greater the influence of fatigue damage on the dynamic compressive properties of concrete materials.The dynamic increase factor-strain rate relationship under the coupling of fatigue damage degree is proposed to provide material data support for component-level research.