# Out-of-Plane Experimental Study of Strengthening Slender Non-Structural Masonry Walls
## 4 Final Remarks and Conclusions  
This study investigated new strengthening techniques to prevent the out-of-plane collapse of non-structural masonry partition walls in future earthquakes by using flexible adhesives and glass fiber reinforcement. An experimental investigation was carried out to assess the strengthening systems' efficiency regarding the out-of-plane behavior. Quasi-static cyclic tests were performed on eleven full-scale non-structural wall specimens. Three of them were non-strengthened, three were fully surface strengthened with reinforcing fabric (strengthening system A), three were fully surface strengthened with rendering mesh (strengthening system B), one was strengthened with diagonal and horizontal strips of reinforcing fabric (strengthening system C), and one was strengthened with diagonal and horizontal strips of rendering mesh (strengthening system D). A flexible polyurethane-based adhesive in watery dispersion was used for the application of all strengthening systems. The main conclusions can be summarized as follows:  
1. The out-of-plane displacement deformed shape was more continuous when strengthening systems were applied compared to non-strengthened specimens. This is due to a more uniform response of strengthened masonry along the height of a wall. Non-strengthened specimens exposed the composite character of masonry where  
Figure 16: Development of equivalent viscous damping coefficients \(\xi_{H}\) in comparison to the critical damping ratio \(\xi\) obtained from the dynamic forced vibration method: **(a)** Specimens NF-1, NF-2, and NF-3, **(b)** Specimens NF-1A, NF-2A, and NF-3A, **(c)** Specimens NF-1B, NF-2B, and NF-3B, **(d)** Specim NF-1C, and **(e)** Specim NF-1D. mortar joints are the plane of weakness. There, the failure was due to the formation of a plastic hinge in the bed joint at about 2/3 of the specimens' height. The strengthened specimens, on the other hand, developed multiple bed joint cracks in the mid-height area with the constant bending moment. 2. From the cyclic response of tested specimens, an asymmetrical out-of-plane behavior of non-strengthened specimens was obtained, in dependence on the quality of the workmanship, while the behavior of strengthened specimens was close to the symmetrical one. 3. The quality of workmanship (the difference of results for NF-good and NF-poor) can be anticipated in the design practice by considering appropriate partial factors for materials as proposed in EN 1996-1-1 [64]. 4. The out-of-plane load-bearing resistance of non-structural walls, strengthened with systems A, B, C, and D, was increased by 221%, 98%, 65%, and 61%, respectively. Although twice lower, the low-cost system applied on the whole surface of the masonry significantly improved its resistance (A vs. B). For other dispositions of strengthening systems, this influence was negligible (C vs. D). 5. The maximum mid-height out-of-plane horizontal displacement was increased with strengthening systems A, B, C, and D by 101%, 95%, 149%, and 64%, respectively. 6. Strengthening systems A and D had the greatest impact on the global secant stiffness of the considered wall over the entire range of applied displacement amplitudes. The improvements of 171% and 168%, respectively, were observed. Comparison of hysteresis envelopes with the idealized one reveals that the methodology for idealization adopted from the in-plane shear tests could be used for the approximation of obtained results from cyclic out-of-plane testing. Based on the obtained experimental results, it can be concluded that simple and cost-effective strengthening systems (systems B and D) can easily be applied during regular refurbishment works on slender non-structural masonry partition walls of existing buildings. They act as effective remedial measures and reduce life-threatening risks and economic losses.