Hardness vs Strength for Structural Steels: First Results from Experimental Tests

Cultural heritage protection and restauration are fundamental matters. Intervention design requires preliminary modelling and analysis to carefully simulate the structural behaviour of existing buildings. The identification of constructive schemes is based on direct surveys, whereas direct testing are required to reveal mechanical and physical properties of materials and their degradation status. Clearly, higher knowledge levels correspond to minor penalties in terms of material performances. For metal structures, regulations provide the employment of destructive investigations only. Furthermore, the sampling of specimens often collides with the safety requirements of artifacts. Therefore, there is a strong need for non-destructive investigations, such as the Leeb method, for a reliable in-situ characterization of carpentry steels. A fundamental step towards reaching this aim is represented by the identification of a theoretical relationship between Leeb hardness values, measured in-situ, and experimental tensile strengths. In order to identify a generally valid correlation, data of the past four years were collected from the database of the Tecnolab s.r.l. company. The experimental setup was based on in-situ Leeb analysis followed by samples collection for consequent tensile tests performed in the laboratory. The experimental data, compared to the trend provided by internationally valid guidelines, provide resistances that the regulations tend to overestimate. Therefore, designing an intervention using these resistances would not be on the safe side. Further analyses should be performed to investigate determinants related to in-situ conditions altering the steel resistance with the aim of identifying potential corrective factors.