Assessing the vulnerability of existing Reinforced Concrete (RC) buildings is an increasing need for mitigating seismic risk, as clearly demonstrated by recent earthquakes in Italy (e.g. L'Aquila 2009) as well in other countries.

The knowledge process plays a crucial role for a reliable assessment, so that the required actions to reduce the vulnerability through cost effective interventions can be carried out. An accurate knowledge of RC buildings requires that the geometry of the structural system, the amount and detailing of reinforcement, and the properties of the constituent materials are identified.

This work is addressed only to study the estimation of materials' properties and, specifically, of steel. The study is based on the results of tensile testing performed on more than 120 reinforcing bars extracted from public buildings constructed in Basilicata region in the period ‘50s - ‘80s . The sample, made up of both smooth and deformed bars, is a valuable source of information about the real strength of the reinforcement present in existing buildings.

The variation of the main mechanical properties is analyzed along various time intervals, always distinguishing smooth and deformed bars. In addition, a comparison is made between the results obtained in this work and the results obtained using as information source results from original acceptance test reports. This comparison, based on a series of statistical tests, shows that small differences can be found, thus confirming the low variability of the steel mechanical properties when compared to the in-situ concrete properties. From this result useful directions on the appropriate number of tests to be performed on steel can be derived, in order to reliably assess the seismic vulnerability of existing buildings while keeping the number of steel specimens to be extracted as low as possible.