Innovative buckling safety verification method for the determination of second-order effects in slender FRP reinforced columns including effects of FRP creep

This paper presents a novel model for the determination of second-order deflections of slender concrete columns, longitudinally reinforced with FRP reinforcement bars, based on the nominal curvature method (NCM) as implemented in Eurocode 2 for steel reinforced concrete columns. A comprehensive study of the differences between FRP reinforced concrete (FRP RC) and steel reinforced concrete (RC) structures serves to introduce the buckling safety verification method as the underlying approach. Before deriving a proposal for a design model, the recalculation of a set of 96 experimental results from the literature is used to validate the approach. The joint evaluation of axial load-slenderness and axial load-curvature curves at different parameter combinations is carried out to elaborate a proposal for the FRP RC curvature (1 / r ) FRP,0 . Based on this formulation, an equation for the analytical determination of the second-order effects in slender FRP RC columns is derived, only depending on the newly formulated FRP mechanical reinforcement ratio m tot,f and the acting axial load DE. Integrating the long-term material properties of FRP reinforcement and the concrete into the model, an FRP creep coefficient of K phi,FRP = 1.055 is determined to account for the FRP creep induced increase in deflection. The model proposal is completed by the derivation of slenderness limits A lim , below which second-order effects can be reasonably neglected. The combination of the different parts results in an integral analytical model for the determination of second-order deflections of FRP RC columns, independent of the type of FRP reinforcement.