Seismic Strengthening of the Mirogoj Mortuary After the 2020 Zagreb Earthquake: 3Muri Macro-Model Assessment

The historic mortuary at Zagreb’s Mirogoj Cemetery, built in 1886, sustained moderate damage during the 2020 Mw 5.3 earthquake. Aiming to preserve heritage value while meeting Croatia’s Level 4 seismic safety requirements, the structure was assessed using in situ and laboratory tests followed by macro-element modeling with 3Muri software. The study evaluated four scenarios: (A) post-earthquake damaged state, (B) reinforcement with new masonry and RC walls, (C) partial fiber-reinforced cementitious matrix (FRCM) plastering, and (D) systematic FRCM plastering. Results show that Case B improved Ultimate Limit State (ULS) scaling factors from 0.64/0.56 to 0.92/0.90 (X/Y), while Case D raised them to 1.03/1.17, satisfying Eurocode 8 and national renovation criteria. Systematic FRCM application improved story shear capacity by up to 57% and shifted failure modes from brittle shear to ductile rocking. Partial plastering proved insufficient, highlighting the need for comprehensive global retrofitting. While the solution is minimally invasive and reversible, uncertainties remain regarding long-term durability and out-of-plane performance. This hybrid retrofitting strategy offers a replicable model for heritage masonry buildings in seismically active regions.