Dynamic Damage Properties Of Concrete Under Different Working Conditions

Concrete structure was used in dynamically complex stress states under the effect ofearthquake excitation, wind-induced vibration, equipment and traffic facilities loads.There is a big difference between actual stress states of materials and the static mechanicstheory when analysis the structural response in current engineering field. Problems instructure dynamic damage mechanism, damage description, and safety of actual stress stateremains to be further research.Scholars at home and abroad carried on a lot of researches on physical andmechanical properties of concrete under the effect of different strain rates, admixture, workenvironment.But the results are mostly limited to the properties of concrete under uniaxialdynamic compression, only a few scholars studied dynamic damage characteristics ofconcrete.As the effect of test facilities, previous experimental study very few,the testresults are not sufficient, the dynamic damage characteristics of split strength and cyclicloading study more less.Concrete material forming process is often accompanied bycorresponding initial damage, concrete loading damage actually is a process ofaccumulating damage, the existence and development of damage has an importantinfluence on the properties of concrete.Therefore, it is necessary to strengthen the reseachof concrete dynamic damage constitutive and damage characteristics under different loadtypes.For the comprehensive system research of concrete dynamic damage char-acteristics, this paper of different batches of concrete specimens were carriedout under different strain rate uniaxial compression test, splitting tensile test, cyclic loadingtest. The main research contents include the following aspects:1) Concrete dynamic uniaxial compression test were carried out under different strainrates (strain rate of10-5/s,10-4/s,10-3/s,10-2/s).Based on the definition of concrete elasticmodulus and energy dissipation as damage variable parameters, and preliminary analysishas carried on damage characteristics, then based on Guo Zhenhai damage model andimproved Weibull-Lognormal damage model has conducted the thorough research to theconcrete damage evolution law.2) Dynamic splitting tensile test of concrete was carried out under different strainrates(strain rate of10-5/s,10-4/s,10-3/s,10-2/s), and acoustic emission signal for material produced was collected by using acoustic emission system in the process of loading.Thesplitting tensile dynamic damage characteristics were preliminary studied from the aspectof acoustic emission energy and the degree of damage. Splitting tensile damage criticalpoint was determined by use of damage model on the basis of the search interval method.Three different tensile stress-axial strain full curve model were established, thecorresponding damage model was constructed and advantages and disadvantages of threekinds of damage model are discussed. At last, A comparitive analysis has been done aboutsplitting tensile damage evolution rules through reasonable damage model of concrete.3) Dynamic cycle and unloading test of the concrete was carried out under differentstrain rates (strain rate of10-5/s,10-4/s,10-3/s,10-2/s),the corresponding acoustic emissionsignals were collect at the same time of loading.The characteristics of stress-strain curveand the relationship between acoustic emission signals and stress levels were thoroughanalysed, and the relationship between cumulative residual strain and the number of cyclicwas studied. A single loops unloading damage model about the number of cycle wasestablished by using the cumulative residual strain relationship with cyclic number andcollecting the number of AE hits. By study the properties of concrete damage on thehysteresis loop, the accuracy of the one-parameter model was further verified.