Title:
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Modelling and computational aspects of the nonlinear finite element analysis of general concrete structures
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The thesis is mainly concerned with the Finite element static and dynamic
models for the behaviour of reinforced concrete using non - associated flow
rule. Applications of these models to the analysis of plates and some threedimensional
problems are reported. The thesis can be broadly divided into
four parts. The first part describes the geometric and material nonlinearities,
and the non symmetry of stiffness matrix arising from the use of non associated
flow rule. Some techniques are proposed to achieve symmetry by the use of
scalar measures, such as incremental work done, plastic multiplier and a non
associator corrector. The performance of these techniques is illustrated by
a wide range of problems ranging from granular materials such as soils and
concrete, to non granular materials such as metals.
The second part of the thesis gives the description of the model for static
behaviour of concrete. A five parameter model is adopted for the yield criterion,
while the modified Drucker Prager function describes the plastic potential
function. A work hardening plasticity, reflecting the multiaxial stress state is
adopted and an energy recovery strategy for unloading (during crack closure)
is reflected in the model. The model is examined by a number of numerical
examples.
The third part gives the description of a model for the dynamic behaviour
of reinforced concrete. The rate sensitivity of such material properties as the
elasticity modulus, yield stress and fluidity parameter are highlighted and the
parameters involved are identified using some existing experimental data. The
model is implemented in a three dimensional program and used in analysing
some numerical examples.
The fourth part of the thesis is devoted to the study of some model response
to various factors, the choice of which is user dependent. Such factors include
mesh discretisation, time and load increment size, numerical integration rule
etc. Some conclusions that could be beneficial to the program user are arrived
at. The inclusion of such information in a user - manual may be of some help
to the the program user, who may be unaware of the inherent assumptions
made in the model and program development.
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