CONSTITUTIVE MODELING IN ANALYSIS OF CONCRETE STRUCTURES
The finite element method has provided a powerful tool to nonlinear numerical analyses of engineering structures. However, the inadequacy of the mathematical constitutive material law turns out to be a major obstacle in concrete structural analyses. Although significant progress on the constitutive modeling of concrete behavior has been made, no unified treatment of the existing mathematical models has been attempted, from which a comprehensive three dimensional constitutive relation can be formulated. Therefore the objective of this research work is to develop a relatively comprehensive and sophisticated model to describe concrete's deformational and strength behavior. The proposed elastic-plastic-hardening-softening constitutive model lies its basis on the plasticity theory, in which the strain-hardening behavior is modeled and formulated by stress-space plasticity while the strain-softening behavior is by strain-space plasticity. Features of the present model include the use of the most sophisticated Willam-Warnke five-parameter or Hsieh-Ting-Chen four-parameter model as the failure criterion; a yield surface with closed shape; a nonuniform hardening rule; a hydrostatic pressure and lode angle dependent plasticity modulus; a nonassociated flow rule; a dual criterion to identify the failure modes; linearly tensile softening for cracking; multiaxial softening for mixed failure mode. It has been found that the model predictions of the work-hardening stress-strain behavior are in good agreement with experimental results involving a wide range of stress states and different type of concrete. The most important inelastic behaviors of concrete, including brittle failure in tension; ductile behavior in compression; hydrostatic sensitivities; and volumetric dilation under compressive loadings are included. It has also been found that the model can also predict a reasonable trend of strain-softening behavior in biaxial and triaxial compressive loadings with relatively low hydrostatic pressure. The proposed model has been coded in a finite element program available for concrete structural analysis.
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