VERIFICATION OF EXCESSIVE VIBRATIONS ON UNIDIRECTIONAL PRECAST RIBBED SLAB FLOORS

Resumo

The ribbed slabs (RS) are one of several types of precast slabs. This type of slab is suitable
for any work, but is very much used in small housing and commercial buildings. The construction
system, composed of reinforced concrete ribs, stands out economically when compared to structures
cast in loco, whether they are solid or ribbed, since they require a smaller amount of framework and
shoring, and reduce the consumption of concrete. From the design point of view, these slabs are often
only verified in relation to the ULS and the SLS of deflection, however when the verification of this
SLS of vibration is neglected, it results in vibration comfort problems and, in some cases, may cause
malfunction of machines and equipment. In this context, this work aims to study the static and dynamic
behavior of the RS’s by means of a parametric analysis that evaluates the influence of the useful height,
topping slab thickness and characteristic strength of the concrete (fck) in the natural frequency variation,
through an analytical and numerical approach (via SAP2000®

). The results were discussed comparing
the analytical prediction of the limit values proposed by ABNT NBR 6118:2014 and PCI Design
Handbook (2010). The results show that with the adoption of additional reinforcement, RS's present
worse results for vibration SLS in relation to deflection SLS, fortifying the need to verify the dynamic
behavior.