Análise da confiabilidade estrutural de vigas de concreto armado utilizando coeficientes de ponderação inferiores aos previstos pela NBR 6118:2014

Abstract

The Brazilian standard for reinforced concrete structures design, ABNT NBR 6118 (2014), uses a design method based on limit states, where the uncertainties related to the strength of materials and the structural actions are indirectly supplied by means of partial safety factors. These factors can guarantee acceptable safety for the structure; on the other hand, when poorly defined, they can lead the structures to a risk state, or cause their oversizing. Currently, both ABNT NBR 6118 (2014) and some foreign standards, such as EUROCODE 2 (1992), use probabilistic methods to assess the safety of structures and calibrate partial safety factors. The objective of the present study was to evaluate, by means of a probabilistic method, whether the use of the resistance partial safety factors predicted by ABNT NBR 6118 (2014), as well as some lower than predicted factors, would keep the flexural beams structurally safe. Firstly, it was conducting a theoretical survey about the flexural design of reinforced concrete beams according to ABNT NBR 6118 (2014) and probabilistic analyzes focused on structural safety, more precisely, Monte Carlo numerical simulation and structural reliability. Subsequently, the flexural design of a set of generic beams was performed, using the standard partial safety factors of resistance, as well as some factors with lower values. Afterwards, the structural reliability analysis of these beams was performed using the Monte Carlo numerical simulation method using MATLAB software. Finally, the structural reliability index of each beam was determined and parametric analyzes of some variables considered in the study were performed. The results showed that the strength partial safety factors predicted by ABNT NBR 6118 (2014), for beams under normal design under flexural design, maintained the beams with acceptable safety, and that in beams subjected to small variable actions (1,5 kN/m² on the slabs supported on them), the beams maintained acceptable safety even with the use of some lower factors than those provided for in the standard (sic).