Dynamic assessment of the axial force in the tie-rods of the Milan Cathedral

The Milan Cathedral, constructed over a period of more than 400 years, is one of the few Gothic cathedrals where permanent metallic tie-rods are installed under all naves to support a portion of the lateral thrust exerted by vaults and arches. After the recent failure of one tie-rod, an extensive research program was carried out to characterize the metallic material and to evaluate the axial forces and the tensile stresses of the tie-rods through dynamic testing and system identification. After a description of the methodology adopted in the dynamic assessment of tie-rods in the Milan Cathedral, the paper presents the main results of the investigation, in terms of fundamental frequencies and axial forces in the tie-rods.