On the shear lag effective breadth concept for composite hull structures

The aim of this paper is to study the concept of shear lag effective breadth of plating, widely applied in the scantling assessments of metallic ship structures, for the special case of composite hull stiffened plating. Indeed, geometries and material behaviour are rather different and the definition of the effective breadth is worthy of investigation. A broad literature survey highlighted that the case of composites is almost not covered by previous studies and that only simplified empirical formulations are proposed for effective breadth evaluations in the rules of classification societies. Thus, suitable finite element models were created and validated to investigate the behaviour of the effective breadth of stiffened laminates when varying geometrical and other typical parameters of composite made ship structures. It was found useful to switch from stresses to strains in the effective breadth definition, considering the anisotropy of the material. An extensive sensitivity analysis allowed assessing the effect of parameters governing the phenomenon. Eventually, regression formulae are proposed summarising the outcomes and possibly applicable in design scantling practice