Advanced single-strut modelling of lightweight in-filled RC frames: validation and seismic performance assessment

Accurate numerical simulation of masonry-infilled reinforced concrete (RC) frames is essential for seismic performance assessment, particularly with modern lightweight infill systems like hollow clay bricks (HCB), gypsum blocks (GB), and autoclaved lightweight concrete (ALC) panels. This study presents an advanced single-strut macro-modeling framework, implemented in SAP2000, designed to overcome the limitations of conventional approaches in capturing the distinct nonlinear behavior of these systems. The core innovation involves the development of material-specific nonlinear axial hinges, meticulously calibrated against the full-scale experimental dataset from Cai et al. (J. Earthq. Eng. 23(9):1531-1559, 2019) to replicate crushing (HCB), shear-sliding (GB), and slip-hardening (ALC) mechanisms. The calibrated model demonstrates high predictive accuracy, with errors in lateral capacity and initial stiffness below 10% for all systems. Leveraging this validated model, a comprehensive comparative seismic performance analysis was conducted. The results quantify a critical performance trade-off: HCB infills increased initial stiffness by 471% but exhibited brittle failure, while ALC panels provided superior ductility (µ = 5.39) and stable energy dissipation up to 4.06% drift. The gypsum system confirmed its seismic inadequacy due to abrupt strength degradation. The study concludes that the proposed modeling strategy provides a reliable tool for performance-based design and analysis, enabling engineers to efficiently conduct parametric studies and evaluate the seismic viability of different infill systems at a fraction of the cost and time of full-scale testing.