STRUCTURAL SLAB OPERATION STUDY

Abstract

A number of factors affect the redistribution and value of axial forces in the cores of structural slabs, such as the location and quantity of supports, the presence or absence of prestress in the structure, the shape of the base crystal of the slab, which is the forming element, and the height (thickness) of the slab, which can be varied within certain permissible limits. A change in one of these features with the rest of the parameters remaining unchanged significantly changes the stress-strain state of the structure. The paper describes the description of finite element models of a structural grid slab with a plan dimension of 12.0×24.0 m. Four models of the slab are adopted, differing only in one parameter ‒ the thickness of the structure. The following values of the structure height were adopted: 1.5 m (model No. 1), 1.3 m (model No. 2), 1.1 m (model No. 3), 0.9 m (model No. 4). The analysis and design  of all models were performed, which were accepted. New profiles of the structural groups of rods were selected so that they met the check conditions for the first and second groups of limit states and the percentage of rod cross-section utilisation was as high as possible. The maximum deflections of the models after the analysis were compared. The lowest weight as an optimality criterion is the most common criterion for  structures, in particular metal structures, as this criterion is quite easy to formalise.

The weight of each slab model was calculated and it was found that the optimal design solution is model No. 1 with a height of 1.5 m, since only for this model the deformability is within the permissible limits. The model characterised by the lowest weight is model No. 3, but the maximum vertical deflection of this structure is greater than the maximum limit.

In conclusion, the analysis of the displacements of the slab model nodes revealed that only the maximum deflection of the slab in model No. 1 does not exceed the maximum permissible deflection of 4.8 cm. The maximum deflections in models No. 2, 3, 4 exceed the maximum permissible value of the absolute deflection. Consequently, the check condition for the second group of limit states is not met in models 2, 3, and No. 4, and model No. 3, which has the lowest weight, cannot be recognised as the most effective among the others. Considering the condition of sufficient stiffness, the optimal design solution is model No. 1. The difference in weight between model No. 1 (8.9 tonnes) and model No. 3 (8.33 tonnes) with the lowest weight is 6.8 %.