Research On The Accumulative Damage Constitutive Of Concrete Material Under Large Strain

Modern earthquake-resistance theory has made full use of the deformability after yielding and the plastic dissipative capability of the structure which can still keep its vertical carrying capacity. This makes the non-elasticity dynamic response of the structure suffering rare earthquake action presents a several times forward and reverse alternate random distortion history, which induces every specimen being in after yielding condition at different levels. In order to accurately simulate this kind of RC structure's dynamic response,many scholars of different countries have gradually studied the hysteristic character of RC specimen in the dynamic response, the constitutive model and the accumulative damage rule of steel and concrete under cyclic loading with different strain levels. Although the accumulative damage characteristic (or called low cycle fatigue character) has close inner relation with the high cycle fatigue character(which has been studied for many years) of concrete under common working stress, the systemic research reports on the behavior of concrete under low cycle fatigue with large strain haven't been found until now. In the research of high cycle fatigue of concrete, the test means of cyclic loading between the set constant or various upper limit and low limit of force or stress has been extensively used. But this kind of test means can't be used to study the behavior of concrete low cycle fatigue under large strain. So the test means of cyclic loading with set strain amplitude (constant or various strain amplitude) need to be utilized, when the strain upper limit is close to the strain e0 (the strain corresponding to the peak stress).In this paper, by this kind of test means, several fatigue tests of concrete prisms under axial compression of large strain amplitude with specified and continuously increased strain upper limit were carried out, the maximum strains beyond e0 of which were under different levels. This paper got the stress-strain curve of every fatigue test specimen in various damage state under cyclic loading with different constant and various strain amplitude, the stress-strain curve of every specimen under initial axial monotonic compression, and the stress-strain curve of distructive specimens under axial monotonic loading after certain cycles. This paper also studied the behavior regression rule of concrete fatigue stress, secant stiffness, maximum strain and hysteretic energy of single cycle and the character points in the whole cyclic loading history. In order to reflect the influence of loading history on the strength , stiffness and hysteretic energy of concrete under cyclic loading, on the base of fatigue tests, this paper has modified the former concrete unloading-reloading constitutive and put up with a kind of constitutive model which are valid under random loading history. And this paper also developed the concrete material stress-strain behavior analysis program according to the above concrete constitutive. The validity and reliability of this constitutive considering random loading history are checked by comparing the calculating results and the test results of two king of cyclic loading tests. So the concrete constitutive of this paper is a effective material constitutive when considering the nonlinear dynamic response analysis of the RC specimen and structure.