Structural reliability theory has long been recognized as the proper tool to guide selection of partial safety factors in limit state structural design codes. Brazilian design codes, however, have never been through this calibration process. This paper addresses the reliability-based calibration of partial safety factors of Brazilian design codes for loads (NBR8681:2003), and for steel (NBR8800:2008) and concrete (NBR6118:2014) structures. The study is based on an extensive dataset of load and strength variables, addressing the Brazilian reality, as much as possible. Calibration minimizes the variations of reliability indexes of the most diverse structures designed according to the codes of interest, with regard to a target reliability index chosen by the analyst. The main result of calibration is to make reliability indexes more uniform, for different design configurations. In case of Brazilian codes, this could be achieved by increasing main variable loads, and reducing the combination values of secondary loads. This paper presents results that are not (yet) recommended for adoption in Brazilian codes, but which should be discussed with the community in order to reach minimal consensus.

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ResumoThis paper presents a reliability-based calibration of partial safety factors for Brazilian codes used in the design of concrete structures. The work is based on reliability theory, which allows an explicit representation of the uncertainties involved in terms of resistances and loads. Regarding the resistances, this study considers beams with concrete of five classes (C20, C30, C40, C50 and C60), three ratios between base and effective depth (0.25, 0.50 and 0.75), three longitudinal reinforcement ratios (ρ min , 0.5% and ρ max ) and three transverse reinforcement ratios ( , and ).In terms of loads, this work considers seven ratios between live loads and permanent loads (qn/gn), and seven ratios between wind loads and permanent loads (w n /g n ). The study also adopts a single value for the target reliability index (β target = 3.0). Results show that the optimized set of partial safety factors leads to more uniform reliability for different design situations and load combinations.Este artigo apresenta a calibração, baseada em confiabilidade, dos coeficientes parciais de segurança das normas brasileiras utilizadas no dimensionamento de estruturas de concreto. O trabalho está fundamentado na teoria de confiabilidade, que permite uma representação explícita das incertezas envolvidas em termos das resistências e ações. No que tange às resistências, são consideradas vigas projetadas para resistir a esforços de flexão e cisalhamento com concretos de cinco classes (C20, C30, C40, C50 e C60), três razões entre base e altura útil (0,25, 0,50 e 0,75), três taxas geométricas de armaduras longitudinais (ρ min , 0,5% e ρ max ) e três taxas de armaduras transversais ( , e ).No tocante às ações, são consideradas sete razões entre os carregamentos acidental e permanente (qn/gn), e sete razões entre os carregamentos do vento e permanente (w n /g n ). O estudo ainda adotou um único valor para o índice de confiabilidade alvo (β alvo = 3,0). Os resultados mostraram que os conjuntos otimizados dos coeficientes parciais de segurança conduzem a uma confiabilidade mais uniforme para diferentes situações de projeto e combinações de carregamentos.Palavras-chave: calibração de norma, estruturas de concreto, confiabilidade, segurança, NBR 6118, NBR 8681.