Análise comparativa entre lajes com vigotas treliçadas e protendidas

Abstract

Precast slabs present great constructive advantages and the prestress applied to its elements increases the positive structural properties to the system. Seeking a comparative analysis of the influence between prestressed and trussed joists in the system through structural, constructive, and financial terms, the advantages and disadvantages from both were related through experimental trials and cost studies. In this study, 6 prototypes of precast slabs were tested, with the length of 2,1 m being 3 slabs with prestressed joists and 3 with trussed joists. The experiments consisted in the application of a load distributed over the transverse section of the simply supported specimens, thus configuring a 3 point flexural test, where the loads and deflections were measured. It was also assessed the compressive strength of the concrete of the cover at 28 days of age, where the results achieved the average fck value of 24,25 MPa, therefore reaching the requirements of the NBR 14859-1, for precast slabs. During the flexural experiments of the specimens it was noticed that due to the precompression of the concrete from the prestressed joists, the slabs containing those elements yielded better results in structural terms. At the first cracking strength the slabs with prestressed joists resulted strength values 110,1% higher than those of the slabs with trussed joists; in relation to the deflection limit established by the NBR 6118, the results were 37,7% superior; and about the maximum supported strength the results were 14% superior. Regarding the cost studies, the direct inputs of the slabs with prestressed elements presented themselves cheaper than the ones with trussed elements, resulting in a 29,0% inferior value per square meter of slab. The cost reduction is also evident in the service compositions referring slabs with prestressed joists, due to the less falsework needed. Finally, it can be considered that the use of prestressed joists as being more advantageous than trussed joists through structural, financial and constructive terms.