STUDY ON THE INFLUENCE OF DEFECTS ON THE STRENGTH OF METALLIC HISTORICAL TIE-RODS

The presence of discontinuities in historical metallic elements is unavoidable owing to their ancient steel-making processes, which produced flaws ranging from microscale (i.e. cracks, inclusions, porosities, micro voids) to macroscale (i.e. welded joints to connect different bars). Therefore, an adequate assessment of their state of conservation cannot leave aside the understanding of the effects induced by material defects on the structural integrity. This work deals with the prestigious case study of historical metallic tie-rods of the Duomo di Milano. Because no information was available on the considered material, particularly dealing with fracture toughness, i.e. the property of withstanding brittle fracture in presence of a flaw, an Elasto-Plastic Fracture Mechanics (EPFM) approach, based on the J-Integral formulation, was investigated to take into account the larger scale of plasticity. This study is coordinated with another one exploiting NDT inspection techniques, to outline, in a damage tolerance perspective, a procedure for the structural assessment of historical metallic tie-rods.