Compressive behaviour of eccentrically loaded slender masonry columns confined by FRP

Fibre Reinforced Polymer (FRP) confinement represents an effective tool for retrofitting masonry piers or columns enhancing their structural performance. This technique has been widely studied in the literature mainly with reference to short columns, while no extensive information is available on the influence of second order effects on its efficacy in case of slender members. Within this framework, the presented study concerns a simplified method able to assess the effects of FRP confinement on the compressive behaviour of slender masonry columns. A proper constitutive law of FRP confined masonry in compression is adopted for performing a sectional analysis, in which also considerations are made on the increase of ultimate moment and curvature depending on the role of some key parameters. The effect of column slenderness is evaluated using a simple analytical iterative procedure, making it possible to calculate the allowable slenderness ratios as function of the maximum drift, taking into account both strength and stability. The effect of slenderness on eccentrically loaded columns is finally examined through a finite element model used for validating the results of the proposed analytical procedure, allowing also to draw safety domains useful for design/verification purposes. It is shown as the column's slenderness affects the efficiency of confinement, being the latter negligible for values of normalized length greater than 20.