Did Material Properties Contribute to the 1284 Collapse of Beauvais Cathedral? A Comparative Assessment of Stone Masonry, Mortar Behaviour and Structural Vulnerability

The partial collapse of the choir vaults of Beauvais Cathedral in 1284 has been explained through structural and constructional hypotheses, but the role of the materials has never been tested against laboratory data. The objective of this study is to quantify, with a transparent probabilistic framework, whether the properties of the stone and the lime mortar could have contributed to the collapse. Four material-dependent mechanisms are assessed—crushing, differential shortening between coursed masonry and monolithic shafts, time-dependent deformation under eccentric load, and the dependence of the buttressing on stone strength—using a traceable database that combines published tests on chalk representative of the Beauvais stone, data on air lime mortars, the documented geometry of the choir and field measurements of the masonry bond. Uncertainty is propagated through 105 Monte Carlo simulations and expressed as central and characteristic safety factors and reliability indices. The central safety factor of the choir piers against crushing is 4.3 for the dry stone and 2.5 for the saturated stone, far below the margin implicit in earlier analyses. Coursed masonry shortens about 4 to 6 times more than a monolithic shaft in the long term, which, under strain compatibility, concentrates stresses of 2.5 to 5 times the mean value in the shafts. Creep-induced amplification is small in a laterally braced pier but becomes critical if lateral restraint is lost. The results indicate that the material did not cause the collapse through lack of strength but is compatible with a material contribution through its deformability and its sensitivity to water.