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Civil-Comp Proceedings
ISSN 1759-3433
CCP: 86
Edited by: B.H.V. Topping
Paper 179

Structural Behaviour of Reinforced Concrete Ribbed Slabs

W.C. de Paula1, M.E. da N. Tavares2 and J.G.S. da Silva23

1Post-graduate Programme in Civil Engineering,
2Structural Engineering Department,
3Mechanical Engineering Department,
State University of Rio de Janeiro, Brazil

Full Bibliographic Reference for this paper
W.C. de Paula, M.E. da N. Tavares, J.G.S. da Silva, "Structural Behaviour of Reinforced Concrete Ribbed Slabs", in B.H.V. Topping, (Editor), "Proceedings of the Eleventh International Conference on Civil, Structural and Environmental Engineering Computing", Civil-Comp Press, Stirlingshire, UK, Paper 179, 2007. doi:10.4203/ccp.86.179
Keywords: waffle slabs, reinforced concrete, concrete structures, concrete ribbed slabs, computational modelling, finite element analysis.

Nowadays the structural analysis of slabs using numerical methods is routine in designs offices. The calculation and design with the aid of software is practically indispensable, owed mainly to the rhythm imposed by the contracting parties of the project and the need to evaluate the possibilities of different structural systems seeking, in that way, the one with the best economical viability.

The choice of the slab type to be used in the construction depends on the designer's experience; in such a way that satisfies the architectural, safety and economy criteria fully. The ribbed slabs consist of a series of small closely spaced reinforced concrete "T" beams framed into girders [1,2].

The "T" beams (called joists or ribs) are formed by creating void spaces in what otherwise would be a solid slab. Voids may be formed using special steel pans. The girders which support the ribs are built as regular "T" beams. Since the strength of concrete in tension is small and is commonly neglected in design, elimination of much of the tension concrete in the slab by the use of the pan results in a saving of weight with little alteration in the structural characteristics of the slab.

The behaviour of these slabs when the number of ribs is varied is considered. The system structural behaviour is also investigated when the edge beams torsional stiffness is modified. The grillage analogy method was used in this investigation because it is easily assimilated by the structural designers and very well represents the structure studied. The mesh used in the numerical analysis presented all the bars of the model coinciding with the center of the ribs [2].

In this paper, a parametric analysis of a reinforced concrete ribbed slab model called REDUZCON [3] was made and the influence of several relevant parameters in the elastic-linear analysis of these slabs was investigated. This system makes use of an inverse cylinder metallic cap named the reduced concrete cap [3].

Through the parametric analysis, the important factors for the grillage analogy model are determined: the boundary conditions; torsional inertia of the system (ribs and edge beams); geometry of the edge beams; and the number of transverse ribs. The influence of the sides ratio was also considered. A comparative study considering slabs modelled using beam elements; or both beam and plate elements was also performed [2,4].

Franca A.B.M. and Fusco P.B., "The ribbed slabs in the Modern Buiding Construction", Ed. AFALA & ABRAPEX, São Paulo, Brazil, 1997.
Paula W.C. de, "Análise Estrutural de Sistemas de Laje Nervuradas de Concreto Armado", MSc Dissertation (In Portuguese), Post-graduate Programme in Civil Engineering, State University of Rio de Janeiro, UERJ, Rio de Janeiro, Brazil, 2007.
Ribbed Slabs REDUZCON - In: URL, Rio de Janeiro, Brazil, 2006.
ANSYS, "Swanson Analysis Systems", Inc., P.O. Box 65, Johnson Road, Houston, PA, 15342-0065, Version 10.0, Basic analysis procedures, 2nd edition, 2003.

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