| Based on Modified Compression Field Theory(MCFT), F. J. Vecchio’s Group fromUniversity of Toronto conducted a nonlinear finite element analysis on reinforcedconcrete by means of smeared rotated crack model, low-order element and the totalsecant stiffness iteration method, and they obtained satisfied results. When2D elementprogram was used to analyze structures with prominent plane features, such as panels,walls and the like, by nonlinear finite element analysis method on the basis of theModified Compression Field Theory, computed results are good, as well as columnswith small axial compression ratio (0.15). However, structures with prominent3Dfeatures, like shear walls with long flanges and columns with large axial compressionratio, cannot be well simulated by2D elements. the total secant stiffness iterationmethod which considered residual strains of concrete hysteretic constitutive relationunder tension and compression led to numerical problems, which are not solved well. Itwas not content to simulate hysteresis effect of panels, columns and so forth, either.Based on Modified Compression Field Theory, this paper applied FEAPpv by Prof.Taylor of UC Berkeley into the nonlinear finite element analysis on panels, walls andshort columns with3D solid element, for that kind of element is able to simulate stressproperties of structures and reflect actual element unitary. Results were also discussed toverify the correctness of the program.Main works of this paper are as follows:①In order to simulate hysteresis effect of concrete better, residual strains ofconcrete under both tension and compression were taken into account and rules ofhysteresis was modified, by reference to researches on hystereic constitutive relation ofconcrete and reinforcement, conducted by Noguchi Hiroshi from Chiba University,Japan. Set the difference between strain in previous load step and that in current loadstep as increase in strain so that stress of concrete and reinforcement can be computedunder that strain.②It is necessary to store series of history variables during operating hystereticconstitutive of concrete and reinforcement. But manual judgment on history of strain isrequired to supply correct route, because it cannot deal with the influence of plus-minusalternation in solving principle strain and direction vector of strain with Jacobi Method.This paper used angle difference of principle strain between previous step and current step to judge and process to ensure that strain in every principle strain directioncorresponds with hysteretic route in this direction.③No load pattern based on secant stiffness iteration method existed in FEAPpv.According to theories in this paper, load patterns of force method and displacementmethod on the basis of the total secant stiffness iteration method were added intoFEAPpv, in order to compute both ascent and declining stages, so that status in periodsafter peak value can be better simulated.Achievements in this paper are shown below:①Substituted existed iteration method based on increase tangent stiffness inFEAPpv by iteration method based on the total secant stiffness. Nonlinear finite elementanalysis with low-order brick element with eight nodes based on average stress-strainwas realized.②Took residual strains of concrete under both tension and compression within thescope of hysteretic constitutive of concrete and reinforcement. Applied origintranslation technology to solve numerical problems and guarantee the stability ofconvergence.③Approaches used to deal with displacement of supports in Structural Mechanicswere introduced into displacement algorithm and added into FEAPpv to analyze withboth force loading pattern and displacement loading pattern.④Monotone and hysteretic simulation of shear panels, shear walls and shortcolumns was done by the program written in this paper and the correctness andeffectiveness of the program was verified. Comparative study on hysteretic rules andrestriction of concrete was conducted. |
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