Iron alloys and structural steels from XIX century until today: Evolution of mechanical properties and proposal of a rapid identification method

Mechanical properties of materials, as provided by current design standards, are the pre-requisites for the proper identification and structural assessment of existing buildings and civil engineering works. For mechanical characterisation, in case of “Limited Knowledge” (KL1) without direct information on the material properties, the usual features according to the standards at the construction time are considered. This is the case, for example, of structural metalworks characterised by historical and artistic interest (bridges, roof galleries, covered markets, railway stations, etc.) or industrial archaeology buildings where, because of the constraints imposed by the National Authorities of Cultural Heritage Preservation, extensive or exhaustive in-situ tests cannot be performed. This paper focuses chronologically, from the XIX century until today, on the evolution process of ferrous alloys, namely cast iron, wrought iron and steel, for structural applications. After a description and classification of the aforementioned materials and their production processes, the main mechanical properties and design stresses for bending and compression elements are briefly analysed and collected in a chronological order. Reference is made to the product specifications and design codes, integrated with data from extensive experimental testing. The resulting database can support realistic assumptions about materials and their properties, used over a range time of over 100 years, once the age of building is known. Finally, a methodology for identifying existing metal carpentry structures, which combines the database with fast non-destructive testing methods, is proposed. Such an approach can be effectively used not only for historical steelworks, but also for the mechanical characterization of structural subsystems or elements (e.g. beams, columns, lintels, tie rods) in common existing buildings made of either steel or steel-rc composite structure.