Cross-Validation of Manual Crack Monitoring vs. Continuous SHM on the Dome of Santa Maria del Fiore

The preservation of historic structures demands reliable data on their structural behaviour over time. For decades, visual inspections and manual crack measurementshave been the standard tool to assess masonry buildings’ stability, nowadays substituted almost completely by continuous Structural Health Monitoring (SHM) systems. A systematic comparison between these two monitoring approaches over long monitoring horizons remains rare. This study presents a cross-validation between the historic manual crack measurements, performed four times per year, and a 35-year continuous displacement monitoring dataset, collected four times a day, on the Dome of Santa Maria del Fiore in Florence. The two datasets offer complementary perspectives on the behaviour of long-standing crack pattern in the Dome’s masonry. Manual measurements provide a discrete yet longer-running observational record, whereas continuous displacement monitoring captures more in detail seasonal cycles and small-magnitude variations that remain unnoticed in sparse surveys. The examination of both datasets together highlights how their combined use can support the identification of persistent trends and offer a broader context for understanding apparent anomalies. Reflecting on this case study, several implications emerge for the long-term assessment of historic masonry. Cross-validating traditional inspections with continuous monitoring can enhance confidence in observed behaviours and offer guidance for monuments where continuous SHM is absent or only recently available. This combined perspective aligns with current priorities in cultural-heritage resilience, where multi-scale and multi-temporal information is essential for informed conservation decisions.