Reliability analysis of reinforced concrete slabs designed according to NBR 6118

Abstract

NBR 6118 (2014) is the Brazilian standard that guides the design of reinforced concrete structures and adopts semi-probabilistic methods as a reference. These establish safety criteria that confront internal forces resulting from actions, increased by majoring coefficients, with the characteristic strengths of steel and concrete materials also reduced by minoring coefficients so that the former is equal to or less than the latter (Sd≤Rd ). However, unlike the Brazilian standard, the international standards determine the calibration of these coefficients through probabilistic methods. This calibration is a factor of paramount importance concerning the measurement of the risk of the structure. It is known that the material's properties present a certain level of dispersion. Depending on the workmanship quality, there are also uncertainties regarding the geometry of the structural parts. Furthermore, the actions in the structure show considerable variation throughout its useful life. In this context, one of the objectives of this work was to determine the reliability of reinforced concrete slabs designed according to NBR 6118 (2014), with loads determined by the recently updated standard NBR 6120 (2019), through a probabilistic analysis using a Finite Element numerical model and through a non-linear analysis. For this, the proposed study addresses the determination of resistance, represented by a theoretical distribution adjusted from simulations generated by the Monte Carlo Method using the ANSYS software. The reliability indices were obtained using the FORM method. As a result, it was possible to verify that most slabs are above the reliability indices indicated as acceptable by the American standard ACI 318 (2014). In addition, the significant influence of the variable loading on the results was confirmed due to its great variability.