An acoustic emission approach to the structural health monitoring of historical metallic tie-rods

The application of Non-Destructive Testing and Structural Health Monitoring systems in historical buildings is of great interest due to the need to guarantee safety and conservation. The present memory focuses on the case study of the historical wrought iron tie-rods of Duomo di Milano, Italy. In recent years, two of these elements presented critical failures. Consequently, a monitoring methodology based on acoustic emission was defined. First, the fracture toughness of wrought iron was characterized by employing standard small-scale specimens taken from one of the failed tie-rods. Meanwhile, acoustic emission was acquired to define a methodology for detecting and localizing the damage events, separating those due to background noise by applying suitable pattern recognition algorithms. Subsequently, a tensile test was performed on a full-scale section of the same tie-rod. Before and after the test, phased-array ultrasonic testing and magnetic particle inspections were carried out to identify and map defects and their possible development due to load application. Finally, it was possible to conclude that magnetic inspections allow identifying the presence of surface defects effectively, phased-array testing estimates the geometry of the defect accurately, and acoustic emission is a promising technique for monitoring the structural integrity of historical metallic tie-rods.