Nonlinear Finite Element Analysis of Concrete Structures

- 1G0 -
cracks with different directions exist at the same location, is
essential. The only observed disagreement with experimental
evidence was a considerable overestimate of the thickening of
the beams. Consideration to dowel action through the shear
deformation of the bars did not change this finding. In combination
with the conclusions from the panel analyses, it implies
that dowel action must be treated through the bending of the
bars and not by their shear deformation. However, to describe
bending of bars by means of the simple elements used here,
knowledge of the displacement fields in two subsequent elements
is required. The resulting increase of the bandwidth of the
equation system make? nuch an approach prohibitive. This problem
may be overcomed using more complicated elements, where the
displacement fields in itself can describe bar bending.
The Lok-Test was the last structural problem that was analysed
and compared with experimental data. This pull-out test is used
to determine the in-situ compressive strength of the concrete.
In accordance with the experimental evidence, it was shown that
the failure load of the pull-out force is linearly related to
the compressive strength of the concrete. It was demonstrated
that the reason that this relation is linear and not proportional
is a result of the increasing ductility and the increasing
ratio of tensile strength to compressive strength the weaker
the concrete. The analysis showed that the failure is caused by
crushing of the concrete and not by cracking. Moreover, use of
the modified Coulomb criterion resulted in some underestimate
of the failure load. Finally, consideration to a realistic
strain-softening behaviour in the post-failure region wes again
found to be of extreme importance.
Regarding general aspects of constitutive modelling of concrete,
the present study has shown that inclusion of an accurate
failure criterion is very essential. Moreover, the consideration
of strain softening in the post-failure region turns out to be
of extreme importance.
The ultimate load capacity of structures has been the quantity
of primary concern here. To give an impression of the accuracy