We focus on reinforced-concrete frame buildings featuring pivots (pilotis). A common refurbishment technique in these structures involves strengthening masonry infills against out-of-plane failure by applying anti-overturning composite grids.

While this intervention effectively reduces the local seismic vulnerability of the infills to out-of-plane expulsion, it can inadvertently increase the global seismic vulnerability of the building. By stiffening the infills, the retrofit enforces a stronger interaction between the masonry panels and the RC frame, potentially worsening the overall seismic response—especially when infills are absent at ground level, where a soft-story mechanism may be triggered.

Through advanced multi-level modelling of the infill panels, we demonstrated this possible detrimental effect on global behaviour. To address it, we propose a global retrofitting strategy based on the addition of conventional bracings or fluid viscous dampers at the pivot (pilotis) story.

References

• [Margiacchi F., Salvatori L., Orlando M., De Stefano M., Spinelli P. (2016). Seismic response of masonry-infilled steel frames via multi-scale finite-element analyses. Bulletin of Earthquake Engineering, 14(12):3529-3546]