Numerical modeling of dynamic behavior in a bi-axial hollow slab

Resumo

Bi-axial hollow slab is a technology that reduces the amount of concrete by replacing it with plastic
spheres with voids on their inside in areas where it does not perform substantial structural function. This technique
leads to material economy and self-weight saving, without considerable inertial loss. As a result, this method
is increasingly becoming more present in the matrix of Brazilian construction methods, due to its efficiency in
technical, economic and environmental aspects. One of the main loads that a structure is subjected to is dynamic
excitation caused by human interaction, such as walking, jumping and running, which are characterized by being
periodic and low frequency. With that, the spread of this technology depends on a reliable numerical modeling
that describes these behaviors, so that structural designers can have confidence in their work. As a relatively new
technology in Brazil’s business, the lack of commercial software that has computational models of cross sections
with spherical voids makes it difficult to popularize this constructive method. In this context, this work aims to
develop a mathematical model that describes the structural dynamic behavior of the hollow slab. To that end, four
finite element models were created, and their dynamic properties of vibration modes and natural frequencies were
compared to an experimentally tested hollow slab specimen. The models I, II, III and IV were elaborated with
frame, shell-thin, shell-layered and solid element, respectively. The results presented in this paper show that the
vibration modes were similar, but with different values of natural frequencies compared with the specimen. The
lowest variation was obtained by the model IV, with a 0,60% difference for a 6,7 Hz frequency relative to the
first mode of the experimental hollow slab. Models I, II and III varied by 8,92%, 1,34% and 43%, respectively.
Therefore, it can be concluded that, among the numerical models analyzed in this work, the one that best describes
the modal behavior of a bi-axial hollow slab it’s the model IV, with finite shell-layered elements, although model
II presents good precision too. This opens up a possibility for reliable modeling of the dynamic behavior of this
type of slab.