Rigidity of partially concreted steel beams and steelreinforced floors

The use of steel-reinforced (composite) floor structures with partially concreted steel beams and prefabricated flooring elements is an effective solution in terms of reducing the material consumption and increasing the structural rigidity. The experimental results of partially concreted composite beams and beams as part of full-size ceilings are studied and analyzed herein. It is shown that the stiffness graph of simple steel-reinforced concrete beams of any shape can be divided into 3 stages: an initial stiffness drop, normal operation, and transition to the limit state with subsequent destruction. The boundaries of these stages are identified for each beam type. The stiffness of the combined cross-section of the partially concreted beam with the rod reinforcement is calculated using well-known formulas from regulatory documents. The element rigidity without rod reinforcement is determined with the decreasing coefficient. Tests of full-size ceilings with partially concreted beams and prefabricated floors confirm the possibility of using standard formulas for the stiffness calculation. However, the width of the compressed concrete flange should be taken into account by less than 3 times than for monolithic slab. The destruction of bending composite structure is accompanied by plastic deformation in flanges of I-beam, destruction of compressed concrete and steel–concrete interaction. However, it does not lead to zeroing of its rigidity. When residual stiffness reaches the ultimate strength state, it is at least 60–70 % of its normative value. This rigidity can be used for the progressive collapse analysis of buildings.

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