Parametric Evaluation of the Effective Breadth for GRP Beams with FEM Calculation

The direct scantling of reinforced plates can be performed by simplified grillage theory or by FEM codes. The first approach gives satisfactory results and better matches Classification Society Rules. The only problem is represented by the determination of beam geometry which implies the determination of the shell portion cooperating with the reinforcement. The width of this strip, called “Effective Breadth Be”, depends on several geometric characteristics like the shell thickness t, the beam span L, the beam distance B and the dimensions of the beam transverse section. In the case of steel plates the relationships between the above parameters and Be is well known and several procedures are available in literature and provided by the Classification Societies rules for determining the effective breadth. More uncertainties exists for what GRP structures are concerned. In this case the only references are represented by semi empirical Classification Societies formulas which give Be just as a function of the shell thickness. For this reason, and in cooperation with the Italian Classification Society, an investigation on this matter has been started by the author considering both single skin and sandwich shells. The analysis has been performed by FEM calculations on a number of numerical models each of them obtained by a different combination of the values of the considered parameters that are: the shell thickness t, the L/B ratio and the transverse section dimensions of the beam. The results have been presented on diagrams with Be/B ratio versus L/B ratio with different combination of the evaluated parameters. A comparison of the curves with the values provided by Classification Societies has been performed as well. Finally all the results have been utilised to obtain a regression curve by which it is possible to evaluate the Effective Breadth by considering all the considered geometric characteristics.