Seismic soil–structure interaction impacts on damage state of infilled wall structures considering in-plane and out-of-plane behaviour

This study investigates the influence of seismic soil–structure interaction (SSI) on the damage state of unreinforced masonry (URM) infill walls in reinforced concrete (RC) buildings, with particular focus on the interplay between in-plane (IP) and out-of-plane (OoP) behaviour. A series of nonlinear time-history analyses are conducted on five-, ten-, and fifteen-storey RC buildings subjected to bi-directional earthquake ground motions. The structural models incorporate nonlinear fibre-based frame elements, a simplified macro-model for infill walls capturing IP–OoP interactions, and an Equivalent Linear Spring–Damper (ELSD) model for the subsoil. An automated element removal algorithm is implemented to simulate the collapse of infill walls during seismic excitation. Comparative analyses between fixed-base and SSI models reveal that while SSI tends to reduce base shear demands, it amplifies lateral deformations, especially in taller structures. This results in increased damage levels in infill walls, including higher instances of soft-storey mechanisms and OoP failures. The findings highlight the necessity of incorporating SSI effects into seismic design for accurate structural performance assessments and improved structural resilience. • Nonlinear seismic analysis of RC frames with URM infill walls is conducted. • Effects of SSI and in-plane/out-of-plane infill interaction are studied. • IP–OoP macro-model includes collapse via automatic element removal. • Soil flexibility is modelled using an ELSD-based SSI approach. • Damage prognosois analysis of infill and structural members is carried out.