Keywords: deformation, model, strength, resistance, stress-strain, material, strengthening, hypothesis, slip, cold-punched, transformed, diagrams.

Currently the most appropriate way of improving and perfecting reinforced concrete design methods is by considering a cross-section deformation model which incorporates full material deformation diagrams. This maximizes the utilization of material strength properties (and in some cases this results in reasonable economy in the use of building materials) and makes it possible to carry out assessment of the structural cross-section 'stress-strain' state not only at the ultimate limiting state but at all loading stages of the structure. This reinforced concrete design method fully eliminates the main shortfalls of the currently used reinforced concrete design method which is based on the classical theory of reinforced concrete structures, whereby the stress-strain state of structural cross-sections is considered only at the ultimate state [1].

This method is based on the method of section and on a cross-sectional material deformation model which makes it possible from one universal point of view to compute reinforced concrete structural elements of any cross-sectional shape, with different types of reinforcements and concrete. Apart from the force equilibrium equations, this method also takes into consideration section deformation conditions and the actual material deformation diagrams of concrete and reinforcements.

This paper contains the results of one of the main objectives of a research work carried out with the main aim to 'develop a method of design calculations for in-situ cast concrete floor slab systems with profiled steel sheetings based on the use of material deformation diagrams' [2]. This objective was 'the establishment of experimental data supporting the relevance of using unprestressed high strength reinforcing bars in in-situ cast reinforced concrete floor slabs as additional reinforcement'. One-way floor slabs with combined reinforcement of profiled steel sheetings as external reinforcement and additional high yield steel bars were experimentally tested for ultimate bending strength to verify the applicability of the proposed method as well as the advantages of using additional high yield reinforcing steel for slabs with external reinforcement.

For the first time a method of computing the slip of the contact interface seam of concrete and the profiled steel sheetings and the cross-section profiled steel sheetings weakening effects of cold-punched anchoring embossment in the form of transformed profiled steel sheeting deformation diagrams was proposed.

A normal cross-section bearing moment capacity design method based on the use of full material deformation diagrams has been established. This method allows determination of stress-strain state parameters of floor slab cross-sections of different configurations composed of different materials at any loading stage. The theoretical and experimental research results have confirmed the effectiveness of using additional unprestressed high strength reinforcing bars in reinforced concrete floor slabs with external profiled steel sheeting reinforcement.

1

N.I. Karpenko, T.A. Mukhamediev, M.A. Sapozhnikov, "Establishment of design method for bar elements based on the material deformation diagrams", In the Book: Optimization design methods for statically indeterminate reinforced concrete structures, Moscow, HIIZHB, 4-24, 1987.

2

E. Chaparanganda, "Strength of in-situ cast floor slabs with external reinforcement", PhD thesis, Belarusian Polytechnical Academy, Minsk, 179, 1999.

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