PSI - Issue 78

Hadi Monsef Ahmadi et al. / Procedia Structural Integrity 78 (2026) 1745–1752

1746

Among these, the use of steel elements has proven particularly effective in improving both the ductility and strength of deficient structural systems (Yang et al.,2025). When strategically integrated — either embedded within or externally bonded to structural members — steel components can substantially enhance load-carrying capacity and deformation tolerance (Terracciano et al., 2015). In unreinforced masonry (URM) buildings, reconstruction is often economically unviable,and the inherent strength of masonry units and bed-joint mortar is limited. The failure behavior of URM walls is highly sensitive to aspect ratio. Low-aspect-ratio walls are especially prone to diagonal tension, compression, and shear sliding failures. Additionally, URM systems exhibit poor cyclic performance, characterized by low energy dissipation and rapid strength deterioration, highlighting the critical need for targeted retrofitting strategies. Therefore, as shown in Fig. 1, externally applied steel strips offer a practical and efficient retrofitting solution. Applied to one or both faces of a masonry wall, these systems address typical failure modes such as sliding along bed joints or horizontal cracking at the base under low axial loads and in-plane lateral forces, which cause rapid strength degradation at small drift ratios. At higher axial loads, increased joint friction suppresses sliding, and diagonal cracking becomes the dominant failure mechanism (Formisano & Longobardi, 2025). (a) (b)

Fig. 1. (a) Unreinforced masonry wall; (b) Reinforced masonry wall with steel strips.

A seminal study by Taghdi et al. (2000) experimentally evaluated the seismic retrofit of low-rise unreinforced and lightly reinforced masonry and concrete walls using externally applied steel strip systems. Their approach employed diagonal and vertical strips anchored through the wall thickness to improve in-plane shear resistance, ductility, and energy dissipation under cyclic lateral loading. Full-scale tests on seven specimens revealed substantial gains in lateral strength — up to 450% in URM walls — alongside significant mitigation of premature sliding and diagonal cracking. Building on these advancements, Borri et al. (2019) introduced a minimally invasive technique using mechanically anchored stainless-steel strips to retrofit masonry panels. Designed in accordance with conservation principles, this method preserved the architectural integrity of historic structures while enhancing seismic performance. Diagonal shear tests on ten full-scale brick and stone panels demonstrated notable gains in lateral strength — up to 113% in stone masonry and 71.8% in brick masonry — particularly when through-rods were used. The reinforcement proved highly effective in the post-elastic range, curbing diagonal cracking and improving ductility with minimal impact on initial stiffness. A simplified design model based on truss analogy was proposed and validated, demonstrating the approach's practicality for heritage applications.