Reliability-based calibration of Brazilian structural design codes used in the design of concrete structures

Abstract

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.

Prospective study on risk-targeted seismic hazard maps for Northeastern Brazil: case study in Zone 1 of ABNT NBR 15421:2006

“…The few existent reliability assessments for structures in Brazil (Beck and Souza Júnior [32]; Santos et al [33],) demonstrated annual failure probabilities ranging from -4 2.15 × 10 to -8 6.80 × 10 , encompassing the two target values adopted herein. Recent reliability-based calibration studies for the Brazilian codes ( [32]; Santiago et al [34]; Santiago et al [35],) adopted -5 2.7 × 10 for the target annual failure probability, which is in fair agreement with the lower bound investigated in this paper. The inferior bound is also consistent with international standards for acceptable individual risk of fatality due to structural failure, a probability of -6 10 per year for low seismicity regions [11].…”

Fatigue safety level provided by Brazilian design standards for a prestressed girder highway bridge

“…The random variables are presented in Table 6, where some of them are Brazilian statistics, as reported by Santiago [25], [26] and Santiago et al [47], [48]. Other variables consider the statistics utilized in Nowak [27] and Wassef et al [8].…”

Safety Assessment of Brazilian Concrete Bridges Through Reliability Analysis

“…Even allowing this reduction, the standard 12 still maintains the quantification of safety based on partial safety factors. Some authors [15][16][17][18] have been concerned with the partial coefficients defined by the standards since they do not reflect the absolute safety that the bridge presents, which could cause the structural verification to reach conclusions that do not correspond to reality.…”