MODELAGEM DE UMA LAJE DE FUNDAÇÃO UTILIZANDO O SOFTWARE DIANA FEA

Resumo

There are several types of structures that can be considered as massive structures. They are
structures for which the effects of the cementitious materials at the early ages, such as heat generation
and autogenous shrinkage, can lead to cracking. There are some ways to avoid thermal cracking in
those structures, such as changing the concrete mix, using a pre or post cooling system, adopting
expansion joints, or increasing reinforcement with iron bars or fibers. The use of fibers increases the
ductility from the earliest ages and thus decreases the cracking potential. The numerical modeling of
concrete in the early ages, including the phenomenon of hydration, naturally implies the consideration
of the exothermic and thermally activated nature of the chemical reactions involved. Therefore, a
numerical model that is capable of anticipate the thermal field in the concrete during the hydration and
subsequent cooling process should be used to analysis massive structures.
In order to study the thermal fields in a ground slab, it was used a FEM software known as DIANA
FEA. A simplified 2D numerical model was developed based on the example presented by Rita [1].
With the optimization through genetic algorithms, the best way to build this slab was studied. This
means the way to build it, with the least probability of cracking. In the model developed in DIANA
FEA, the symmetry was used and the construction was simulated without any pre-cooling or
reinforcement method, using cooling pipes and adopting fibrous concrete. The cracking index (ICR)
corresponding to the first days after the casting of the first and second layers were higher than 1,
indicating that the structure does not tend to crack, as in Rita [1]. However, in the model developed in
DIANA FEA, it was observed that at 26 days, there is already a probability of cracking. For the model
using fibrous concrete, this tendency is observed at 28 days, which corresponds to an improvement
compared to the one without the fibers. In the modeling using cooling pipes, it could be observed a
decrease in the maximum temperature in the core of the structure.