Effect Of Fatigue Damage On Dynamic Tensile Properties Of Concrete

Concrete structures may be subjected to fatigue loading during service,resulting in degradation of carrying capacity.In this case,predicting the structural performance based on the origin material properties would cause greater safety hazards.Therefore,accurate definition of material degradation inducted by fatigue is significant for inves-tigating the impact resistance of concrete structures under initial fatigue damage.In the current research,there are few studies on dynamic concrete properties after fatigue loading,lacking of material models which accurately describe the mechanical behav-iour.According to the mentioned analysis,it is necessary to carry out research for clarifying the dynamic properties of concrete materials under fatigue damage.This paper mainly investigates the effect of fatigue damage on the dynamic ten-sile properties of concrete by means of concrete fatigue tests,meso-scale dynamic nu-merical simulations and static and dynamic splitting tests under fatigue damage.The main research contents and conclusions are as follows:（1）The concrete splitting fatigue test is carried out.According to the test results of fatigue life,the S-N curve is plotted and the concrete splitting fatigue life equation is fitted.On this basis,different degrees of fatigue damage were applied to the con-crete specimens and the quantitative analysis of fatigue damage was carried out.The results indicate that that the degree of fatigue damage quantified by different damage measurement methods is slightly different,but the trend is basically the same.The damage factor defined by macroscopic mechanical properties is slightly higher than that measured by microscopical methods,the decline is about 16%.（2）Numerical simulation is performed using LS-DYNA software.According to the mechanical properties attenuation caused by fatigue loading,the specimen is di-vided into several zones,which feasibility is verified by comparing with the test re-sults.Moreover,the dynamic performance of the partition model and the origin model at different impact velocities are analyzed in detail.The results show that the partition model is basically consistent with the origin model in terms of stress distribution and failure mode,while its strain rate sensitivity is slightly lower.（3）The experiments on the dynamic tensile performance of concrete after fatigue damage is conducted.Using MTS Landmark 370.50 system and INSTRON high-speed dynamic system,the failure modes of concrete specimens under different initial fatigue damage degrees at different strain rates is observed,while the corresponding dynamic splitting tensile strength is acquired.Consequently,the empirical equation for DIF_ft of concrete under different fatigue damage obtained by fitting,the relation formula of DIFft and strain rate with damage factor was established.