Abstarct: Abstract In reinforced concrete (RC) structures, masonry infill walls are typically considered non-structural elements. However, evidence from recent earthquakes indicates that these infills can significantly influence the seismic performance of buildings. Earthquake-induced forces—both in-plane and out-of-plane—can lead to cracking, separation from the frxame, and even sudden failure of the infill walls, which challenges the overall stability of the structure. A key issue contributing to this vulnerability is the weak connection between the RC frxame and the infill. Accordingly, this study aims to evaluate the seismic behavior of RC frxames with clay block infill walls. The experimental investigation explores the impact of strengthening techniques—using glass fiber-reinforced polymer (GFRP), steel angles, and shotcrete mortar—on the structural performance. Specimens were subjected to both in-plane and out-of-plane loading to assess the combined effects of boundary conditions and strengthening strategies on ultimate strength, effective stiffness, ductility, and failure patterns. he results of the in-plane loading tests indicated that the presence of masonry infill increased the ultimate strength of the frxame by 42.05% and its stiffness by 158.77% compared with the bare frxame, although its ductility decreased by 71.48%. Under out-of-plane loading, the strengthened infill exhibited approximately 104.18% higher strength, 104.29% higher stiffness, and 6.23% greater ductility compared with a fully restrained infill. Relative to an unstrengthened two-sided infill, strength, stiffness, and ductility increased by 136.12%, 96.8%, and 61.10%, respectively, indicating improved stability, reduced lateral deformation, and enhanced energy dissipation capacity. Under combined in-plane and out-of-plane loading, the two-sided strengthened infill displayed the lowest ultimate strength (9.64) and stiffness (0.438), but the highest ductility (2.73), demonstrating highly ductile behavior and superior energy absorption. These characteristics make such configurations suitable for structures exposed to dynamic and impact loads, such as industrial facilities or buildings near blast sources. Overall, the findings confirm that strengthening masonry infills with GFRP and steel angles—when applied with proper detailing—can effectively enhance their seismic performance and contribute to improved safety in RC structures subjected to earthquakes.