Dealing with Uncertainties in the Assessment of Existing RC Buildings

Abstract

From a literature review it has been possible to point out, starting from Greek and Latin literature references, the development of at least 160 catastrophic seismic events in the Mediterranean area in the last two century. Studies and researches have shown that about 60% of such events have been recorded in Italy as well as more than 50% of the recorded damages. This data can be ascribed to the high intensity of the recorded earthquakes in Italy, but also to both the high density of population and the presence of many structures under-designed or designed following old codes and construction practice: for this reasons the seismic risk in Italy is very high. In fact, the seismic risk is defined by the convolution of three terms: hazard vulnerability and exposure. The hazard is linked to the probability that, in the analyzed area, a seismic event occurs in a given period of time. The vulnerability, also known as fragility, is related to the propensity of people and goods to be injured or damaged during a seismic event. The exposure is rather closely related to the aftermath analysis of a seismic event and in particular to location, consistency, quality and value of goods and activities on the territory that may be affected directly or indirectly from the event of earthquake. Moreover by analysing the data provided by the 14th census of population and buildings (2001) in Italy, it is possible to have a clear idea regarding the period of construction of the existing reinforced concrete buildings; such data show that about one million of building units (35%) have been built before the first code with seismic provisions, Legge 2/2/74 n.64 [1], was issued. As a result a significant portion of the total seismic risk in Italy, evaluated in economic terms, comes from the various type of damages endured by the existing buildings. This is the case for several other European countries in which the average service life for buildings is larger than that of countries like the United States. Therefore, management of existing building stock is a major concern in such regions. This is the reason why, more recent European seismic guidelines (e.g., EC8 [2], OPCM [3], NTC [4]) pay particular attention to seismic assessment of existing structures, which is distinguished from that of the new construction by lack of information about both the original features and the current state of building in consideration. The assessment of existing structures is subjected to numerous sources of uncertainty.