Exploring the seismic performance of corroded RC frames with masonry infills

Reinforced concrete (RC) frames infilled with unreinforced masonry panels are widely used worldwide and represent a prevalent structural typology in several earthquake-prone regions. A large amount of existing RC building stocks in seismically active countries, however, were erected more than 50 years ago with substandard materials, construction practices, and outdated design guidelines, and have likely exceeded their service life limit. Aging RC structures are also particularly vulnerable to environment-induced degradation (including corrosion), increasingly relevant due to climate change, which is projected to further reduce their already compromised seismic performance. Although extensive studies in the last decades highlighted the importance of considering the presence of masonry infills in the assessment of existing RC buildings subjected to earthquake loading, limited investigations are available on the seismic response of such systems when reinforcement corrosion is considered. In addition, as corroded RC frames typically exhibit reduced ultimate displacement, ductility and base shear capacities, it is expected that distinct frame-infill interaction mechanisms would govern under corroded and uncorroded scenarios. Conducting laboratory tests on corroded RC frames with masonry infills, however, is challenging and sometimes even impractical due to technical difficulties and time constraints. In this paper, fiber-based finite element (FE) models were developed to investigate the impact of corrosion on the seismic performance of RC frames with masonry infills at different scales. First, the developed FE models were validated against quasi-static and dynamic experimental tests on intact RC columns and infilled RC frames without corrosion effects. Then, calibrated FE models were validated against experimental tests on isolated RC columns with various degrees of corrosion. Simplified modelling strategies, also applicable in engineering practice, were adopted and validated to account for corrosion-induced damage numerically. Finally, the validated FE models were used to investigate the corrosion-induced degradation of seismic response for corroded RC infills and building assemblies. Results obtained indicate that the presence of infills may not only increase the load bearing and drift control capacities of intact RC frames, but can also improve the structural performance of corroded RC frames, especially in case of strong masonry panels. Corrosion-induced lateral strength capacity loss of bare frames can be up to 8 times larger than that of infilled frames.