Abstract:
The finite element method has provided a powerful
tool to nonlinear numerical analysis of engineering structures. However, the
inadequacy of the mathematical constitutive material law turns out to be a big
problem in concrete structural analysis. Although a significant progress on the
constitutive modelling of concrete and shotcrete behaviour has been made, very
little from these models deal with the effect of the high temperature on
concrete or shotcrete. Consequently, no unified treatment of the existing
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 as well as shotcrete deformational and strength behaviour
under normal and high temperatures. The proposed model is an elastic-plastic-hardening
constitutive model based on the plasticity theory. In this model, the
strain-hardening behaviour as well as the temperature effects modelled and
formulated by stress-space plasticity taking into account the heat and the
kinematic energies. The model adopted the most sophisticated Willam-Warnke
five-parameter model as failure criterion. The present work deals with concrete
or shotcrete shell structures and adopted the Isoparametric Sandwich Shell
Element in finite element formulations. The main features of the model include
the yield surface with closed shape and a non-uniform work-hardening with mixed
hardening rule. By the proposed model, an application on a tunnel for the case
of fire loading was made. This helps to answer many questions about the safety
of the tunnels in case of fires. The results showed that, taking fire loading
into consideration has a great importance for designing concrete tunnel lining.
This is because very high temperatures cause a total failure in some parts of the
tunnel lining.