Nonlinear Time-History Re-Assessment of an Existing RC Frame Building Designed to P100-1/2006 Using 3D Solid FE Models with Explicit Reinforcement: Influence of Masonry Infills Under Vrancea 1977/1990 and Türkiye 2023 Records

This paper presents a nonlinear time-history re-assessment of an existing reinforced concrete (RC) frame building designed in 2007 according to the Romanian seismic code P100-1/2006 and re-checked against current seismic demand. Two three-dimensional solid finite-element models were developed in ANSYS: a bare RC frame and an RC frame with masonry infill panels. A distinctive feature is the explicit representation of longitudinal and transverse reinforcement embedded in the concrete solids, enabling 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 match the P100-1/2013 target spectrum for the investigated site (a_g=0.40g). Modal analysis shows a clear stiffness increase due to infills, with the fundamental frequency rising from 4.4669 Hz (RC) to 5.8680 Hz (RC+M). Under the scaled records, infills substantially reduce global deformation demand: peak roof displacements in the transversal direction decrease from 9.87–14.26 mm (RC) to 2.74–3.38 mm (RC+M), and peak interstorey drift increments decrease from 3.35–4.94 mm to 0.92–1.16 mm, with drift ratios remaining well below conservative serviceability thresholds. Roof peak accelerations also decrease, reaching 0.490 g for RC versus 0.211 g for RC+M in the governing VN90 case. Base-reaction resultants and F_y–roof displacement loops confirm a stiffer global response with reduced displacement excursions for the infilled configuration. Local fields indicate that, in the bare frame, plastic strain concentrates at perimeter column bases and beam ends, while in the infilled model inelastic indicators shift toward masonry discontinuities around openings and panel corners; reinforcement demand peaks at beam ends, column bases, and the staircase region, consistent with torsional participation. The results highlight that masonry infills can strongly govern stiffness and drift demand at current design-level intensity, while introducing localised concentration zones that are relevant for performance assessment of existing buildings.