Optimization of post tensioned unidirectional flat slabs

Resumo

The structural solution for slabs of a building is a very important factor and significantly affects the
total construction cost. The use of prestressed tendons, in particular its unbonded type, has become increasingly
popular, as well as its application to flat slabs because it allows larger spans, greather architectural flexibility
and construction speed and less labor required. Although the prestressed flat slabs have a higher consumption of
concrete in relation to ribbed slabs, they are an attractive solution due to their simple formwork. For an efficient
design, it is necessary to pay attention to the thickness of the slab, the number and layout of the tendons. In this
sense, numerical optimization techniques are appropriated tools to search for an optimal design of flat slabs. This
work presents an optimization model for post tensioned unidirectional flat slab with unbonded tendons according
to the recommendations of NBR 6118:2014, seeking the minimization of material and labor costs. The design
variables are the slab thickness, the number of tendons and the eccentricities that characterize their profiles in
both directions, all of them are of the discrete type. A grid model is applied in the structural analysis, where
the prestressed tendons are treated as equivalent loads. The optimization problem is solved using an open source
genetic algorithm, which is successfully applied to discrete structural optimization problems. The results of the
proposed optimization model are compared with others obtained using the conventional design approach found in
the literature and show an excellent cost reduction.