Safety variability assessment of reinforced concrete beams subjected to bending moment considering the NBR 6118:2014 safety partial factors

Abstract

This paper presents a study about safety of reinforced concrete beams subjected to bending moment and designed with the partial safety factors proposed by ABNT NBR 6118:2014. The main goal was to assess the uniformity in the safety of the beams considering different values for the neutral axis position and the load ratio, by using the Reliability Theory. A simplified procedure to calibrate the partial safety factors was proposed taking into account the nature of each random variable and a target reliability index. From the analysis of the results, an alternative method for the design of reinforced concrete beams was also proposed, in which safety is guaranteed by the using of a probability of failure instead a set of partial safety factors. The results showed the lack of uniformity in the safety of the beams design with de constant set of partial safety factors. The procedures of design and calibration of the new safety factors were capable of to give uniformity to the safety of the beams and to achieve the proper structural configuration with the required safety level.

Structural reliability of a RC beam considering different preliminary designs

“…They found out that, in some cases, the safety levels obtained may be lower than the limits given by the American standard ACI 318 [3] and by the Eurocode EN 1990 [29] even for usual load ratios. They also found that the Brazilian code does not provide a uniform level of reliability, as also presented by other references (Stucchi and Santos [11]; Nogueira and Pinto [16]; Stucchi and Santos [30]).…”

“…Beck and Doria [12]; Beck et al [13]; Chaves et al [14]; Santos et al [15]; Nogueira and Pinto [16]). On the other hand, only a few papers in the literature deal with the fact that the preliminary design of a given structure also have a significant impact on its final reliability.…”

Comparison of two FORM methodologies for reinforced concrete beams under flexure

“…A study on the reliability of reinforced concrete beams designed according to the Brazilian code NBR 6118:2014 was proposed by Nogueira and Pinto (2016). Using the FORM (First-Order Reliability Method), the authors assessed the reliability indexes for beams with different relative positions of the neutral axis (x/d), taking the strength of concrete and reinforcement steel as well as the dead and live loads as random variables.…”