Nonlinear Seismic Reassessment of an Existing Reinforced Concrete Frame Building: Influence of Masonry Infills Under Intermediate-Depth and Shallow Crustal Earthquake Records

This paper presents a nonlinear time-history reassessment of an existing reinforced concrete frame building originally designed in 2007 according to the Romanian seismic code P100-1/2006 and re-evaluated under current seismic demand. Two three-dimensional solid finite-element models were developed in ANSYS Workbench 2025 R2: a bare reinforced concrete frame and an infilled frame with masonry panels. A distinctive feature of the modelling strategy is the explicit representation of longitudinal and transverse reinforcement embedded in the concrete solids, which allows direct tracking of steel stress demand and post-cracking load transfer. The models were subjected to bidirectional ground motions from the Vrancea 1977 and 1990 earthquakes and the Türkiye 2023 earthquake, scaled to the P100-1/2013 target spectrum for the investigated site. The results show that masonry infills markedly increase global stiffness and reduce displacement-related demand, with substantially lower roof displacements and interstorey drift measures in the infilled configuration. The bidirectional response remains predominantly translational, while the local stress and inelasticity fields indicate qualitative concentration zones in the frame, masonry panels, and staircase region. Overall, the study shows that masonry infills can strongly modify the actual seismic response of existing reinforced concrete frame buildings and should be considered explicitly in performance assessment.