Abstract
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.
Highlights
The design of structures can be understood as an iterative process that seeks to establish dimensions and configurations to the constituent elements of the structural system, in which a set of bounds is respected to guarantee the requirements of security, economic, aesthetic, functionality and durability
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 great advantage of this approach is that the limit state method with calibrated safety coefficients based on probabilistic procedures, has transformed the classical integral that defines the problem of structural reliability [7] in a practical and direct way for use in projects, even for professionals who are not familiar with the concepts of the Reliability Theory
Summary
The design of structures can be understood as an iterative process that seeks to establish dimensions and configurations to the constituent elements of the structural system, in which a set of bounds is respected to guarantee the requirements of security, economic, aesthetic, functionality and durability. The design codes adopt a fixed set of partial safety factors that are applied to all structures present in the implementation scope of the code This assumption makes that different types of structural elements designed with such coefficients do not have uniform safety levels for the various limit states. It is possible that the adoption of constants safety factors generates structures with global reliability lower than the recommended minimum values, which is clearly against the security situations [8,9] In this context, Mohamed et al [9] highlighted the lack of uniformity in the safety of pillars in reinforced concrete designed with partial factors proposed by Eurocode 2, considering variations in important parameters like slenderness index, concrete resistance, axial load eccentricity and longitudinal steel reinforcement.
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