Influence Of Strain Rates On Mechanical Behaviors Of Reinforced Concrete Members

Concrete structures are subjected to dynamic loads unavoidably,for example,seismic load,blast load,impact load.Because there are distinct differences between dynamic situations and static situations about the behaviors and stress-strain relationships of concrete and steel materials,reinforced concrete structures or members show different behaviors subjected to the dynamic loading from the static loading.Concrete is a kind of rate dependent material and works in high strain level when subjected to the seismic load or blast load.The stress-strain relationship given by design code of reinforced concrete,which is directly used to analyze the behavior of concrete structures, can not show the effect of strain rate because in the code the effect of strain rate is not taken into account.In this paper,according to the dynamic experimental results of concrete,the stress-strain relationship of concrete given by design code of reinforced concrete is modified by taking account into the effect of strain rate on concrete.Then dynamic behaviors of reinforced concrete members are studied with the modified model.(1) Based on continuum damage theory and damage variable defined by tangent degradation of concrete,the evolution of damage of concrete under different stress rates is deduced.The evolution of damage shows that the damage value increases with the increased strain ratio at the same strain ratio,the damage value decreases with the increased strain strain.(2) Based on the layer fiber model,cracking moment,cracking curvature limit moment and limit curvature of reinforced concrete beam are studied.At the same time,the tendency of the four indexes above with the reinforcement ratio is also studied.During the studying,two situations are considered,â‘ only dynamic characteristics of concrete are consideredâ‘¡dynamic characteristics of concrete and steel are considered.The result shows that dynamic characteristics of concrete has little effect on the cracking moment,cracking curvature,limit moment and limit curvature of moderate reinforced beam but dynamic characteristics of steel has considerable effect on the four indexes above;nevertheless,the dynamic characteristics of concrete and steel has some effect on the four indexes above of over reinforced beam.(3) Envelope curve of axial force-bending moment and moment-curvature curve for reinforced concrete column is study as beam's method and analysis model.Meanwhile,the tendency of limit moment,limit curvature and limit axial force with eccentric distance is also studied.The result of numerical analysis shows that dynamic characteristics of concrete have little effect on the limit moment of Large Eccentricity Column but have considerable effect on the limit moment of Small Eccentricity Column;nevertheless,dynamic characteristics of steel have considerable effect on limit moment and limit curvature of both large eccentricity column and small eccentricity column...