Applicability Of Hysteretic Constitutive Models Of Concrete In Structural Analysis Based On Development Of OpenSees

Numerical simulation analysis is a main method in studying the sesmic behavior ofRC structures. The rationality of concrete models is an important factor to affect theresults of numerical simulation. Due to the complexity of the concrete material, thereare six uniaxial hysteretic concrete models in OpenSees to reflect its mechanicalproperties. However, any comprehensive comparison of these concrete models can notbe found. Therefore, the tasks of this paper are as follows:①By analyzing the six concrete models in OpenSees, the author found that theycan not take into accout of some important hysteretic characteristics, like stressdeterioration, influence of unloading/reloading cycles, etc.②In order to take stress deterioration, influence of unloading/reloading cycles intoconsideration, a rivised simplified model based on Sakai’s concrete model was proposedand implemented in OpenSees. Besides, Blakeley model was partly modified and thenimplemented in OpenSees.③By simulating the experimental results of RC columns under low reversedcyclic loading with the existed concrete models and the simpled Sakai model, influencesof different compression skeleton, hysteretic rules and whether tensile behavior isincluded on simulation results for RC columns under low reversed cyclic loading wereinvestigated.④A series of RC columns with different axial compression ratios and variouslongitudinal reinforcement ratios were designed to study the influences of differentconcrete models on hysteretic behavior of RC columns under low reversed cyclicloading.⑤A typical RC frame was designed according to the provisions of the secondanti-seismic level for regions of seismic intensity VIII prescribed by Chinese buildingcodes. To study the influence of different concrete models on the dynamic response ofRC structures, nonlinear dynamic response analyses of the RC frame under rareearthquakes were performed using different concrete models. Incremental dynamicanalyses of the frame were also carried out in order to reflect the effects of differentconcrete models on dynamic response of the frame as materials enter different degreesof nonlinearity.The analysed results indicated that: ①For RC columns under low reversed cyclic loading, the tensile behavior ofconcrete has great effects on hysteretic behavior, so is the effect of cracked surface. Asaxial compression ratio, longitudinal reinforcement ratio increased, on the contraty, theinfluence of tensile behavior and effect of cracked surface decreased.②For RC columns under low reversed cyclic loading, the difference of hystereticbehavior, caused by the concrete models with different compression skeleton, hystereticrules, increased as the axial compression ratios, lateral loading displacement increase.However, the difference of hysteretic behavior will be decreased as the longitudinalreinforcement ratios increase.③The dynamic responses of RC structures under rare earthquake, are greatlyaffected by whether the tensile behavior of concrete is included. There are almost nodifference between the dynamic responses resulted by compressive concrete modelswith different hysteretic rules on condition that the analyses were peformed withouttensile behavior of concrete in consideration. The difference among the analysed resultswill be very small if the concrete model only differ in tensile softening branch.④The seismic response of RC structures varies with different concrete modelswhen materials enter different degrees of nonlinearity, but no obvious rules.