Assessment of in-line bonded fastening for masonry retrofitting

Fastening systems are widely used to connect structural elements and to retrofit existing structures. Post-installed bars with adhesives are often used in masonry structures to achieve box-like behavior, improving the wall-to-wall and the slab/roof-to-wall connections. In such applications, multiple anchors are typically installed in a line, often with limited spacing. To date, most experimental studies have focused on the behavior of single or double anchors, neglecting the case of linear fastening connection. This paper presents an experimental campaign aimed at studying the behavior of a connection with up to five in-line anchors. M12 threaded rods were installed with an adhesive into solid brick walls with varying masonry strengths. Critical installation conditions were considered, namely, installation in the mortar joint and spacing-to-embedment depth ratio equal to one. The tests were displacement-controlled, and a special system was adopted in some tests to impose a uniform displacement to the linear fastening system. For the low-strength wall, a linear increase in capacity was observed with an increasing number of anchors. In contrast, for the higher-strength wall, the trend was linear up to four anchors, after which an asymptotic value was reached. Finally, numerical analyses were performed to evaluate the effect of various conditions, including the eccentricity of the applied displacement, the scatter of the anchor pullout strengths, and the group effect (interaction between anchors) on the overall capacity of the systems. In general, the interaction between the anchors resulted in the most influential parameter, although the effect remains constant beyond a certain number of anchors (5–6).