Strength and stability of pultruded GFRP elements

• analytical expression for the calculus of critical stress and ultimate moment of a hollow cross-sections stiffened internally or externally with GFRP ribs. • The model considers a compressed cylinder of small thickness composed of a set of meridians and parallels made of GFRP fiber beams connected and interacting with a containment action of the parallels on the meridians. • limits of diameter/thickness ratio of the profile suitable to avoid premature failures due to buckling before material crushing were 10 for a profile without stiffeners and between 18 and 25 for profiles with stiffeners. • The global buckling load increases with the presence of internal stiffeners with increases of up to 100% compared to the case of elements without stiffeners. • In bending, the ovalization of the section significantly reduces the critical moment due to buckling effects and also ovalization increases the flexibility of elements with deflection increased up to 100% with respect to elements without ovalization. . The overall purpouse of this research was the proposal of a simple analytical expression for the calculus of critical stress and ultimate moment of a hollow cross-sections stiffened internally or externally with GFRP ribs. The model considers a compressed cylinder of small thickness composed of a set of meridians and parallels made of GFRP fiber beams connected and interacting with a containment action of the parallels on the meridians. The model also includes the cases of stiffened cross-section for the calculus of critical load for global buckling. Major findings were the determination of limits of diameter/thickness ratio of the profile suitable to avoid premature failures due to buckling before material crushing. Limits were 10 for a profile without stiffeners and between 18 and 25 for profiles with stiffeners. The global buckling load increases with the presence of internal stiffeners with increases of up to 100% compared to the case of elements without stiffeners. In bending, it was found that the ovalization of the section significantly reduces the critical moment due to buckling effects and also ovalization increases the flexibility of elements with deflection increased up to 100% with respect to elements without ovalization. The importance of this study is the proposal of analytical expressions for strength verification of FRP pultruded elements under flexure and axial forces taking into account of second order effects derived though a mechanical model clear also to practioner engineers.