PSI - Issue 78

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

1747

Zizi et al. ( 2021) conducted a comprehensive numerical and analytical study on a steel grid-based retrofitting system for URM walls. The system — comprising thin steel grids bonded to both wall faces using epoxy resin — offers reversibility, ease of installation, and cost efficiency, especially when anchorage to existing floor or roof slabs is feasible. Using a macro-modeling approach in ABAQUS, calibrated with full-scale cyclic shear tests, the study found that the retrofitted walls exhibited up to a 70% increase in ductility and over a 40% gain in lateral strength compared to URM. A detailed parametric analysis linked key variables — such as strip spacing, cross-sectional area, and panel aspect ratio — to seismic performance, culminating in a preliminary design criterion. Jing et al., 2024 explored axial strengthening of unreinforced brick masonry using pre-stressed steel strips. Their retrofit system combined vertical and transverse mild steel strips anchored with binding bolts and pre-stressed via controlled tightening, avoiding the need for specialized post-tensioning equipment. The results showed that vertical pre-compression delayed initial cracking and enhanced axial stiffness, while horizontal pre-tension improved the post buckling performance and raised the ultimate axial capacity by up to 43%. Tests under monotonic axial loading confirmed the efficacy of the combined strip system in achieving stable, ductile, and confined structural behavior. A design methodology based on anisotropic failure criteria under biaxial stress states was proposed to facilitate practical implementation. This study aims to numerically investigate the seismic performance of unreinforced masonry (URM) walls retrofitted with a hybrid system comprising rigid steel strips and ductile thin steel web plates, bonded to both faces of the masonry wall using epoxy resin. The objective is to enhance strength and energy dissipation capacity under nonlinear loading. The research begins with a linear buckling analysis of rigid steel plates with perforated grid patterns, revealing that wider links improve stability. Nonlinear simulations then assess the shear behavior of these elements, highlighting the reduced strength and stiffness of perforated plates and their tendency to deform out of plane. To counteract these effects, thin ductile web plates are added between grid links, resulting in improved shear performance and reduced deformations. Finally, the retrofitting system is applied to a macro-model of a URM wall using ABAQUS 2024. The model of masonry wall is calibrated against experimental data and analyzed under pushover loading. Results confirm that the combined use of rigid and ductile thin steel plates significantly enhances the seismic response of masonry walls while reducing overall steel consumption. 2. Elastic buckling behavior of grid perforated steel web plate under pure shear loads The critical elastic shear buckling force of a steel web plate can be estimated using a theoretical expression proposed by Timoshenko and Gere, (2012). This equation incorporates the shear buckling coefficient, which depends on boundary conditions. For a square steel web plate, the shear buckling coefficient is approximately 9.34 for simply supported edges and 14.58 for clamped edges. In this study, a square steel web plate with a refined mesh was analyzed using linear eigenvalue buckling analysis to evaluate the influence of grid perforation patterns. Both perforated and solid plates were considered, with variations in link width ( Lw = 100 mm, 75 mm, and 50 mm) and four different opening ratios (10%, 20%, 30%, and 40%). The normalized critical shear buckling forces (critical shear elastic force of perforated plate to critical shear elastic force of plate without perforation) were calculated, and after verification, the results were compared for both simply supported and clamped edge conditions, as presented in Fig. 2. As illustrated in Fig. 2, significant differences are observed between the two boundary conditions. In both simply supported and clamped edge scenarios, increasing the opening ratio leads to a noticeable reduction in the critical elastic shear buckling force. While increasing the link width generally enhances the buckling resistance, this effect is more pronounced under simply supported conditions. In contrast, for clamped edges, the influence of link width on buckling strength is comparatively limited, suggesting that edge restraint plays a dominant role in stabilizing the plate against shear-induced buckling.