Concrete Strength Variability in Italian RC Buildings: Analysis of a Large DataBase of Core Tests

Abstract

The knowledge of the materials’ mechanical properties is a preliminary and important step in the seismic vulnerability assessment of existing buildings. In RC structures, the compressive strength of concrete can have a crucial role on the seismic performance and is usually difficult to estimate. Major seismic codes prescribe that concrete strength has to be determined essentially from in-situ and laboratory tests. In some cases such estimation can be complemented by default values in accordance to standards at the time of construction, therefore analysing the actual concrete properties typically found in RC existing buildings realized in different periods can make available useful data. To this end, in this paper attention has been addressed to public buildings, namely schools and hospitals. A large database made up of about 1500 test results on concrete cores extracted from about 300 RC public buildings located in Basilicata region (Italy), has been prepared and analysed. The relationships between the actual strength values (mean and dispersion) and the construction period of buildings have been studied. Theoretical distributions to approximate the discrete distributions of strength values in different construction periods have been determined, thus providing relevant data for the structural assessment of individual buildings and, especially, for large scale vulnerability evaluations.

Criteria for identifying concrete homogeneous areas for the estimation of in-situ strength in RC buildings

“…This confirms the poor reliability of the information obtained from original design specifications or test reports when related to actual concrete properties, as acknowledged in studies dealing with the vulnerability assessment of existing RC buildings (e.g. [18,9]). …”

“…[1], in Europe [2,3], in the United States [4][5][6][7][8][9], in Italy). With reference to the assessment and retrofitting of existing RC buildings, many design codes (e.g.…”

Experimental response and fiber‐reinforced cement composites strengthening of real reinforced concrete columns with poor‐quality concrete

“…Many of the existing reinforced concrete (RC) structures built between the 1960s and 1970s are vulnerable to earthquake loads due to poor material properties, lack of transverse reinforcement, degradation of the structural materials, corrosion of longitudinal reinforcements, cover spalling and reduction of the bearing load capacity . This increases the need to develop reliable assessment procedures and efficient and sustainable repair/retrofit interventions for existing RC buildings …”

Material strength safety factors for the seismic safety assessment of existing RC buildings

“…Given the range of values reported in the literature (e.g. see [20][21][22][23][24]), a CoV fc |N of 0.30 can be considered to be a conservative estimate of the concrete strength variability. According to For the case of reinforcing steel, common values for the CoV|N of the rebar yield strength are generally less than 0.10.…”

“…As shown in previous studies [18][19], estimating the CoV fc |N using a small sample of results from concrete core tests may lead to estimates that do not reflect the real variability of the concrete strength. This fact is even more relevant due to the high value of the concrete strength CoV fc |N that is usually found in existing buildings [20][21][22][23], often exceeding a value of 0.20 [24]. A methodology improving the accuracy of the estimate of CoV fc |N by using rebound hammer tests was proposed in [18].…”