## 1 Introduction  
The aim of retrofitting work is to improve the mechanical performance of a structure or single members of insufficient seismic adequacy. Especially in the case of traditional masonry buildings, the retrofit system must be able to undertake the tensile stresses due to horizontal forces and/or bending/overturning moments. In terms of cultural heritage buildings, the choice of intervention techniques must account for different categories of values and aspects [1]. Moment or braced frames, generally metallic or wooden, are common types of retrofit solutions for low- and medium-rise buildings [2; 3]. Their technical and structural advantages are their high extent of reversibility (mostly depending on the wall-frame connections), good compatibility with masonry, high effectiveness in improving the seismic performance of the building and adaptability to changes in actions or resistances [4; 5]. Moreover, such solutions have a good potential for sustainability because of their efficient use of material and low cost due to their simple design and quick installation. Frame retrofits allow the relief of the masonry from horizontal in-plane actions. Whenever they can be a viable solution (e.g., in cases portrayed by [6; 7; 8]), their performance in increasing strength and ultimate drift could be excellent, provided that the load transfer is effective [9]. From the technical, structural and economic/sustainability point of view, purltruded FRP technology has interesting potential to suit moment or braced frame retrofit applications [10; 11]. However,no significant applications are known so far. In particular, its light weight and immunity to electro-chemical corrosion and organic attack are indeed advantageous with respect to metallic and wooden frames. Pultruded Fiber Reinforced Polymer (FRP) profiles of the first generation--i.e., thin-walled cross sections with T, double T, C, rectangular, square and circular shapes--are nowadays in common use and promptly available from producers. The use of such building elements is increasing, especially in \"all-FRP\" structures like footbridges and pavilions [12; 13], and in hybrid structures matching FRP to, e.g., concrete or glass [14; 15]. However, the availability of seismic design prescriptions is still limited, even if case studies have shown good potential [16; 17]. The reversibility and the structural effectiveness of retrofitting are strictly related to the anchoring system. A wide variety of technical studies exist in the literature, from a general point of view, on anchors and fastenings in concrete and masonry structures, which are of interest for connecting retrofitting frames to heritage buildings [18; 19; 20]. Generally, metallic bolts or bars installed by drilling across the wall's cross-section, with appropriate bearing plates, nuts and washers, can be used for connecting retrofits to existing masonry structures [21]. European technical documents for the design of steel anchors in masonry recommend minimum spacing values, but do not provide specific capacity requirements [22]; the USA's recommendations are oriented towards capacity calculation accounting for tensile, shear or combined loading and different failure modes [23]. Generally, the available literature is useful for the peculiar topic of frame connections to historic masonry walls. Moreover, adhesive connections between masonry and pultruded FRPs are recently receiving attention [24; 25]. Aesthetic preservation is often the most restrictive value in the choice of a retrofit system. Frame-based solutions, which cannot be hidden inside or beneath the structural members they strengthen, are suitable for buildings of low to moderate surface preservation requirements. This study aims to explore the feasibility of frame retrofitting of masonry piers with pultruded FRP profiles.