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Title: Computational plasticity in concrete failure mechanics
Author: Pearce, C. J.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1995
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A constitutive model for plain concrete is presented, centred around a fracture energy based plasticity formulation. The essential ingredients of a concrete strength envelope are realised (such as a non-linear hydrostatic pressure dependence, a non-circular deviatoric trace and a realistic biaxial trace) by utilising the well known Five Parameter Model of William/Warnke as the basis of an Enhanced Five Parameter Model. This model is capable of a complex loading surface evolution for capturing both the pre and post peak regimes of concrete. In particular, the post peak tensile softening is introduced exponentially, controlled by the fracture energy release rate. Several computational aspects of rate independent plasticity, with reference to the Enhanced Five Parameter Model are investigated. Finite stress increments are integrated using a backward Euler stress return formulation, solved by the Newton Raphson method. However, due to the complex nature of the proposed loading surface, this approach has been found not to be fully robust and in need of improvement. As such, controlled scaling of the stress update is introduced as well as improved starting predictions of the final solution via an analytical return to an intermediate auxiliary loading surface. The conditions necessary for discontinuous bifurcation of strain rates are discussed and the localisation tensor is introduced. Furthermore, spectral analysis of the localisation tensor is utilised to predict impending localisation and a scalar failure indicator is proposed to monitor the evolution of discontinuities. With particular application to the proposed concrete model, studies of localisation problems revealed that some form of mesh alignment is essential if impending bifurcation and orientation of discontinuities produced by the localisation analysis is to be resolved. Moreover, the effect on the overall response of a non-aligned mesh is shown to be significant.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available