Marco Gaiotti

An analytical/numerical study on buckling behaviour of typical composite top hat stiffened panels

This paper deals with the buckling strength of typical ship stiffened panels built in fibreglass composite laminates. The results obtained applying analytical formulations based on equilibrium and potential energy equations are compared with the ones obtained by linearised eigenvalue analyses of rather detailed finite-element models. Analytical formulations consider an elementary panel only, accounting for the boundary effects of stiffeners surrounding its edges, while FE models fully describe the interactions among plate and stiffeners as a whole. A sensitivity analysis to highlight the most influencing parameters in the problem is also presented. So far no systematic scantling assessment of buckling behaviour of hull shell and deck panels seems to be recommended by classification societies’ rules for pleasure crafts made in composite materials. Thus, this paper aims at illustrating the application limits of analytical methods, natural candidates to become the basis of rule requirements. Difficulties in the evaluation of torsion behaviour of stiffeners and of corresponding buckling modes involving both the plate and the stiffeners are highlighted. Some concluding suggestions for rule scantling assessment formulations are eventually provided.

Dynamic buckling of masts of large sail ships

The design of sail systems is a fascinating topic that naval architects have been facing since many centuries and nowadays is revived because of the increasing size of modern pleasure and racing yachts. It is hence surprising that empiricism largely drives mast and rigging design even at the present time. Actually, while structural dynamics is explicitly considered in current scantling design of hull structures, this is not usually the case for mast and rigging. However, numerical simulations can now be successfully applied to assess effects of load variations in time. Considering the governing limit states and the typical behaviour of a pre-tensioned slender structure, the dynamic buckling of the bottom panel of a typical large mast is evaluated in this paper, showing significant differences from the widely applied quasi-static approach. The obtained results provide a new perspective for the scantling assessment of sail systems, overcoming the current empirical and prescriptive approach proposed by rules of classification societies and international standards.

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.