Influence of the reinforcement corrosion on the bending moment capacity of reinforced concrete beams: a structural reliability approach

E A P Liberati,C G Nogueira,E D Leonel

doi:10.1590/s1983-41952014000300005

Abstract

Reinforced concrete structures are, certainly, one of the most used types of structure around world. When it is located in non-aggressive environments, it respects, in general, the structural life predicted. Unless the structure be used improperly. However, the durability of these structures is strongly connected to degradation processes whose origin is environmental and/or functional. Among these processes, it is worth to mention those related to corrosion of reinforcements. The reinforcement's corrosion is directly related to the durability and safety of concrete structures. Moreover, the chlorides diffusion is recognized as one of major factors that triggers the corrosion. Therefore, at modelling accurately the chloride diffusion, the corrosion of reinforcements can be better evaluated. Consequently, design criteria can be more realistically proposed in order to assure safety and economy into reinforced concrete structures. Due to the inherent randomness present on chloride diffusion and corrosion, these phenomena can only be properly modelled considering probabilistic approaches. In this paper, the durability of a beam designed using the criteria proposed by ABNT NBR 6118:2003 [1] is assessed using probabilistic approaches. The corrosion time initiation is determined using Fick's diffusion law whereas Faraday's corrosion laws are adopted to model the steel loss. The probability of structural failure is determined using Monte Carlo simulation. The mentioned beam is analysed considering different failure scenarios in order to study the influence of water/cement ratio and environmental aggressiveness on the probability of failure. Based on these results, some remarks are performed considering NBR recommendations and the real probability of failure.

Highlights

Concrete properties, such as versatility in the design of complex architectural geometries, competitive cost when compared to other structural materials and suitable mechanical properties for a wide range of structural requirements, all enhanced with the addition of steel for structural ductility and tensile resistance, make reinforced concrete the most used construction material in the world since the 1950s [2]
The high costs associated with steel loss, structural material mechanical degradation and repair, the loss of structural stability and the recurrence of these problems make the corrosion of reinforcements the principal pathological manifestation in reinforced concrete structures [5]
The mechanical degradation process of reinforced concrete structures resulting from reinforcement corrosion can be divided into two stages: initiation and propagation

Summary

Introduction

Concrete properties, such as versatility in the design of complex architectural geometries, competitive cost when compared to other structural materials and suitable mechanical properties for a wide range of structural requirements, all enhanced with the addition of steel for structural ductility and tensile resistance, make reinforced concrete the most used construction material in the world since the 1950s [2]. This phenomenon is often simplified, without significant loss of accuracy, to a process controlled only by diffusion This problem can be modelled considering the second Fick’s law for diffusion, which requires the following assumptions: the apparent diffusion coefficient is constant over time and homogeneous in space, the concentration of chloride in the environment is constant, and the concrete is assumed to be fully saturated. Several studies have dealt with the problem of reinforcement corrosion affecting only the reinforcement cross-sectional area without considering the concrete damage effect [10,11,12] These methodologies can be considered as preliminary because they do not consider the consequences of corrosion on the concrete mechanical behaviour. This study aims to contribute to the structural durability field, using equilibrium equations defined by a standard code [1], and assess structural safety when mechanical degradation processes are present

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