Density Estimation in Heritage Timber Elements Using Resistograph Drilling Resistance

Accurate structural diagnosis of timber elements in historic buildings requires minimally invasive and operationally reliable assessment methods compatible with heritage conservation principles. This study aims to estimate timber density in situ directly from Resistograph drilling resistance. To achieve this objective, density estimates derived from Woodpecker impact penetration tests were paired with Resistograph drilling resistance measurements through a mesh to develop a point to point correspondence and calibrate a linear model relating density to drilling resistance and enabling its direct application through Resistograph measurements. The database comprised thirteen historic sweet chestnut (Castanea sativa Mill.) beams from the Cloister of Michelangelo in the Baths of Diocletian complex, Rome, Italy. Statistical analyses included the assessment of multiple window sizes, segmented penetration intervals, model calibration, and Leave-One-Beam-Out (LOBO) cross validation. The resulting model enables density estimation using only Resistograph measurements and demonstrated high predictive accuracy, achieving a coefficient of determination of 92%.