Allowable stresses in FRP marine vessels

The publication consists of a literature survey of allowable stresses used in fibre-reinforced plastic (FRP) structures, and a new method for the determination of allowable stresses is presented. In the literature survey, primary attention has been paid to the marine industry (including classification societies), the aerospace industry, and to pressure vessel and pipe standards. Generally the subject is only briefly discussed in the literature. This is a drawback, since the conservatism dominating the rules used today often means unnecessary weight penalties. High factors of safety (FoS), except in the aerospace industry, are used in most designs. The short experience of structures in service, wide variety of material combinations and the rather complicated mechanical behaviour are the most important factors in this regard. The presented determination method for allowable stresses aims at introducing a more rational way for dimensioning. The method is based on the partial factors of safety concept. A statistical analysis can be included for better accuracy. This requires enough data of material and load behaviour. The method is flexible and can be tailored to various needs. One major drawback is the lack of information concerning material behaviour under long-term loads. The method is aimed to be expanded in the future.