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Title: Reinforced concrete failure prediction under both static and transient conditions
Author: Damjanic, F. B.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1983
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This thesis is concerned with the application of finite element techniques to the solution of nonlinear thermal and structural problems. Special attention is given to the analysis of reinforced and prestressed concrete structures under both static and transient thermal loading conditions. Problems conforming to both planar and axisymmetric conditions are considered. The first part of this thesis is concerned with the finite element analysis of transient thermal problems in solids. The spatial discretisation is based on a Galerkin procedure using isoparametric finite elements. For the time discretisation generalized "mid-point" two level schemes are employed and their numerical stability and accuracy are examined. Sources of the instability and inaccuracy are identified and certain modifications are suggested to improve the numerical performance. The concept of a "penetration depth" in determining the element mesh size is introduced to ensure the numerical solutions which are both accurate and free from spatial oscillations. The use of reduced numerical integration in the solution of thermal transient problems is also examined by the corresponding eigenvalue analysis, and a possibility of obtaining accurate and computationally economical solutions using reduced integration is proposed, This is particularly beneficial for a thermal-mechanical analysis. Finally, in the first part of this thesis, the mapped infinite elements are introduced in the thermal transient analysis of unbounded domain problems. The second part of this thesis is concerned with the finite element analysis of nonlinear structural mechanics problems. At first, the finite element displacement formulation is briefly reviewed, and a general elasto-visco-plastic material model together with an incremental time-iterative nonlinear solution technique is presented. The numerical stability of this algorithm is then examined and practical criteria for selecting the maximum time step length which provides both a stable and accurate solution are proposed. The above solution algorithm is extended for the nonlinear analysis of reinforced and prestressed concrete structures under short-term loading conditions. Simple constitutive material models are proposed to simulate the nonlinear behaviour of concrete and reinforcing steel. The concrete model includes tensile cracking, tension stiffening effects, reduced shear stiffness associated with both crack interface effects and dowel action, as well as nonlinear multiaxial compressive behaviour, viscoplastic yielding and crushing. The steel reinforcement bars or prestressing cables are modelled by line or membrane elements lie within, or at the surface of, the standard isoparametric elements. The steel is assumed to behave as a one-dimensional elasto-viscoplastic material in both tension and compression. Finally, a solution technique for the transient thermal-mechanical analysis of reinforced and prestressed concrete structures is developed. The technique, which in fact embodies all the formulations and schemes previously discussed and examined, involves concurrently solving an uncoupled set of equations (the transient heat conduction equations and the incremental equilibrium) within a time interval to provide both the temperature and displacement increments. The use of a fully coupled theory is avoided, but the sequential approach allows the material properties to be temperature dependent. Several numerical examples are presented for all types of the analysis considered and the comparison is made with analytical or experimental results whenever possible.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available