Cracking, damage and strain localization in concrete structures

Chen, Gongfa. (2001). Cracking, damage and strain localization in concrete structures PhD Thesis, School of Engineering, The University of Queensland.

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Author Chen, Gongfa.
Thesis Title Cracking, damage and strain localization in concrete structures
School, Centre or Institute School of Engineering
Institution The University of Queensland
Publication date 2001
Thesis type PhD Thesis
Supervisor Graham Baker
Total pages 259
Language eng
Subjects 090506 Structural Engineering
Formatted abstract
      This thesis deals with strain localization problems in concrete.

      Strain localization is a stability problem. It may be either a bifurcation problem (as for the uniform stressed case) or a limit point problem. As a bifurcation point is reached, the distributed solution loses the stability and gives way to a localized solution. An energy criterion is presented in this thesis to govern the post-bifurcation path. Among the kinematically admissible post-bifurcation paths, the structure follows the one that renders the energy increment global minimum. The equivalence between this criterion and Bazant's maximum entropy criterion is proved.

      This energy principle is applied to the bifurcation analyses for the simple cases, some of which are beyond the Hill's bifurcation criterion. The principle is also applied to the simple lattice model to capture the localized solutions among all the kinematically admissible post-bifurcation paths without introducing imperfections. With the softening constitutive law, the bifurcation phenomenon occurs not only in conventional plasticity theory but also in the non-local plasticity theories. The energy principle is applied to the bifurcation analyses for conventional plasticity theory.

      In this thesis, two non-local plasticity theories, the gradient dependent and Cosserat micro-polar, are studied. An incompatible element for the gradient dependent plasticity is proposed to reduce the degrees of freedom. The phenomenon of the multiple equilibrium paths in Cosserat plasticity theory is found and the characteristics of the solutions are studied.

      In summary, this thesis elucidates the fundamental differences between the strain localization caused by material non-linearity and geometrical non-linearity; establish the energy principle to reflect the instability of the localization; constitute effective numerical FEA algorithms to capture strain localization; and investigate the effectiveness of the solutions of the regularized plasticity theories. Major contributions made in this research include: (1) realizing that the significant difference between the mesh-dependency and the imperfection-dependency (i.e., the localized solution depends on where the imperfection is introduced), the former is expected to be solved by regularized theories while the later can only be solved by the energy minimization strategy; (2) realizing that even the regularized solutions in Cosserat and the gradient dependent plasticity theories do not really capture strain localization.
Keyword Concrete.

Document type: Thesis
Collection: UQ Theses (RHD) - UQ staff and students only
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Created: Tue, 28 Sep 2010, 13:15:50 EST by Muhammad Noman Ali on behalf of Social Sciences and Humanities Library Service