Estudo dos estados limites de serviço em lajes pré-moldadas de concreto com vigotas tipo trilho

Abstract

This study aims to verify the limits imposed by the service limits of excessive vibration and excessive deformation in accordance with ABNT NBR 6118 (2014) for precast concrete molds with rail-type studs and using the maximum permitted use limit. predefined constructive typology. An analysis was performed using three dimensional computational models through finite element method with the aid of SAP 2000 V18 software. Two constructive typologies with rail and prestressed portholes, with a height of 8 cm and spacing between studs of 30 cm were tested. Two concrete compression layer thicknesses were tested, 4 and 5cm. The concrete used is of class C25 and the others used were used according to ABNT NBR 6118 (2014). The use load adopted was 1.5 kN / m². For different relationships between the slab spans, the maximum usable length for the tested typology was calculated from the limiting states of vibrations and excessive arrows. Depending on the state of excessive vibration limit it is possible to use for spans type rail 4.5 meters, both for 4 and 5 cm cover, above this slab length the natural frequency is below 4.8 Hz, which is the critical frequency of vibration for this case. For prestressed joists it is possible to use spans of 5.5 meters for the 4 cm compression table and 6 meters for 5 cm cover, both with 25 Mpa fck. For slabs with rail and prestressed joists it is possible to use spans of 4.5 and 5.5 meters, respectively, respecting the state of excessive vibration limit, but to respect the excessive deformations, taking into account the deferred arrow in time, it is possible to use spans of 2 and 3 meters.