# Safety Evaluation of Existing R.C. Buildings: Uncertainties Due to the Location of In Situ Tests
###### Abstract  
The paper aimed to investigate the influence, on the assessment of the structural safety level of an existing _rc_ building, of the different choices that the technician in charge of a structural evaluation (the \"analyst\") can make regarding the structural elements to be tested to obtain a prescribed level of knowledge. To this end, the case study of a reinforced concrete framed structure built in the 1960s in Italy was investigated by means of numerical analyses. The probability distribution of the estimated safety levels was evaluated in the paper by means of a Monte Carlo approach, considering the alternative selections of elements done by a large number of analysts, and the probability of unsuccessful safety estimations is discussed for the knowledge levels considered in the Italian technical codes and the Eurocodes. confidence factor; assessment of seismic safety index; Monte Carlo simulation; existing buildings 20242024/12/24/2  
number of combinations of investigated elements and of points within the same element may be chosen, depending on the technician's criteria and/or for logistic reasons. This is an intrinsic source of uncertainty, even neglecting other aspects that can have effects on the results of experimental investigations, such as the environmental conditions in which the tests are performed, the instruments utilised, and several other elements depending on the chosen technique [8; 9; 10]. Therefore, for the same knowledge level, a huge number of different experimental results may be obtained, and, consequently, for each different combination of experimental data, this may correspond to a different value of the assessed safety level of the building with respect to seismic events. For random uncertainties, usually, codes suggest discrete knowledge levels with the aim of describing the availability of information on the existing building examined. Based on the acquired knowledge level, two possible approaches are suggested by standards: the amplification of the force demand or a reduction in the materials' resistance. For example, FEMA-356 [11] prescribes the introduction of a knowledge factor, dependent on the acquired knowledge level, which amplifies the force demand. However, for the random uncertainty of mechanical parameters--which is the focus of this paper--the Italian technical codes [1; 2], ASCE 41-17 [3], and the Eurocodes [4] introduce a confidence factor (CF) which reduces the mean resistance of materials as provided by on-site tests, with the CF depending on the knowledge level (KL). A larger value of CF is suggested by such codes for a lower number--and therefore a lower representativeness--of the tests carried out. In detail, the codes define three knowledge levels based on the number of acquired data: KL1 is limited knowledge, KL2 is extended knowledge, and KL3 is full knowledge. It is worth noting that different values for the confidence factor correspond to the different knowledge levels. According to the Italian technical code [2] and the Eurocodes [4], the confidence factor related to limited knowledge is \(\text{CF}_{\text{KL1}}=1.35\), while the confidence factor corresponding to extended knowledge is \(\text{CF}_{\text{KL2}}=1.20\) and the confidence factor corresponding to full knowledge is \(\text{CF}_{\text{KL3}}=1.00\). The possibility of taking into account the many uncertainties that arise in the procedure for the seismic safety assessment of existing buildings with a single confidence factor applied to material strengths has been, and is still, widely debated in the scientific literature [12; 13; 14; 15; 16]. In detail, starting from the approach proposed in [12], the present research explores the effects of uncertainties related to the choice of on-site test locations on the assessment of seismic safety indexes.