PSI - Issue 78

Ahmed Mabrouk et al. / Procedia Structural Integrity 78 (2026) 960–967

965

curves, and detailed tracking of frame and infill limit state exceedances. This structured post-processing enables a direct comparison between infill strategies and sets the foundation for the results discussed in the following section. 4.4. Results The average infill PL ratios across increasing PGA levels for the URM- and F-infilled configurations are presented in Fig. 4. These results illustrate the effect of strengthening on infill behavior. In the URM configuration, OOP collapse ( ) occurs at = 0.3 following the exceedance of the . Consequently, data for PGA levels of 0.4g and 0.5g are excluded from the plots. This exclusion reflects the fact that, once OOP collapse is triggered, the infill struts are removed from the model and no longer contribute to the structural response — making any subsequent evaluation of IP performance for these panels numerically undefined. In contrast, for the F-infilled frame, only the is exceeded at = 0.5 , indicating the increased capacity provided by the retrofit system in both IP and OOP directions. Fig. 5 presents the average frame PL ratios across PGAs for all three configurations: bare frame (BF), URM infilled, and F-infilled. For the BF model, PL ratios increase steadily with seismic intensity, with column curvature emerging as the dominant damage mechanism. However, the response for = 0.5 is not included in the plots due to convergence issues in some of the ground motion records. Since not all analyses completed successfully at this intensity level, the resulting averages would not reliably reflect the true structural response. Both infilled configurations show improved performance due to the initial stiffening effect of the masonry panels, resulting in lower curvature and drift demands relative to the bare frame. However, this benefit diminishes as damage accumulates, especially in the URM model. In the infilled frames, the dominant failure mode gradually shifts toward column shear. Notably, the F-infilled frame can delay the onset of drift- and flexure-related limit states up to = 0.5 , demonstrating the positive influence of infill strengthening. Overall, the results confirm the dual role of infills while unreinforced masonry panels contribute initial stiffness, they are susceptible to early OOP collapse; in contrast, strengthened panels substantially improve both nonstructural and structural perfo rmance. These findings validate the model’s capability to capture infill– frame interaction, progressive degradation, and failure mechanisms under varying seismic intensities, and highlight the importance of incorporating infill strengthening strategies in the seismic retrofit of traditionally designed RC buildings.

Fig. 4. Average infill performance level ratios, for infilled frame configurations