Behaviour of reinforced concrete flat slabs
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AbstractThe behaviour of flat slabs is investigated. Three aspects are studied: the analysis, the deflections and the shear strength of flat slabs. To achieve this, a new test set-up is used to test two 5 m multispan full slabs. The test set-up facilitates the testing of a part of a slab centred about an edge column and the adjacent interior column. By providing edge restraint around the periphery of this area the behaviour of the full slab can be simulated. Boundary frames provide these edge restraints. The first slab is tested three times and repaired after the first two failures. Shear failures happened at the interior and edge column connections with and without shear studs. In addition, four isolated edge column-slab connections are tested to failure. The test variables are the distribution of the flexural reinforcement and the load eccentricity. Tests from the literature are used to study the different parameters affecting the punching shear strength of slab-column connections. The results are compared with the provisions of the ACI, BS, CSA and CEB-FIP Codes and new shear strength equations reflecting these parameters are proposed. For interior slab-column connections subjected to shear and moment transfer, a correction factor for y v (portion of unbalanced moment resisted by shear stresses according to the American and Canadian Codes) is proposed. This correction factor accounts for the effects of the reinforcement ratio on y v. A new method for calculating y v for edge column-slab connections is proposed. The method is based on a truss model. Also investigated is the use of a plastic she~ stress distribution along the shear critical section. Regarding the analysis of flat slabs, the most common methods used (Equivalent Frame, Direct Design, Prismatic Member and Finite Element Method) are presented and their predictions are compared with the results of the two slabs tested. Improvements for the Prismatic Member Method are suggested. For the deflections of flat slabs, the most common methods (Effective Moment of Inertia, Bilinear Method and Mean Curvature Approach) are critically reviewed. The deflections predicted by these methods are compared with the test results and modifications are proposed.
Bibliography: p. 361-370.