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Possible way to obtain particular performances suitable for specifics design requirements
2012-07-29 08:22:09

Composite materials have a high trend of diffusion in civil engineering since they offer various types of product and material characteristics. Using different types and quantities of fibers coupled with various resins for the matrix, it is possible to obtain particular performances suitable for specifics design requirements.

Therefore the necessity for design guidelines and code provisions is urgent, in order to allow effective utilization of the products with the right degree of structural safety.
In particular, Fiber Reinforced Plastic (FRP) profiles obtained with the pultrusion technique represent a product with interesting properties of durability and lightness, but also economic if the glass fibers are used. On the other hand these benefits are coupled with a structural behavior completely different from that of steel profiles  traditionally used in civil engineering, making the well-known design rules and models totally invalid for the FRP profiles.

Pultruded profiles are realized with most of the fibers oriented along the axial direction of the element defining very different mechanical characteristics in the longitudinal and transversal directions; the mechanical behavior is elastic up to failure.
According to the fibers’ direction, the strength and elastic constants are much higher than those in the orthogonal direction, where the resin characteristics govern the problem; furthermore the ratios between the strength and the elastic moduli are very much higher than in the case of steel. As a result, the strength is not usually used, and failure conditions are attained for buckling phenomena; it is also clear that the design rules for avoiding buckling phenomena cannot be the same as those of steel that usually occur in the plastic range, with the influence of mechanical and geometric imperfections due to the steel working process.

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