The cover thickness design of concrete structures subjected to chloride ingress from RBDO solution technique

Abstract

Diffusion is the principal transport mechanism of chloride ions into concrete pores. The chlorides trigger the reinforcements’ depassivation when its concentration at the concrete/reinforcement interface reaches the threshold level. Thus, the depassivation defines the initiation stage end and the propagation stage start. The structural safety reduces widely during the propagation stage because of the various deleterious mechanisms triggered by reinforcement’s corrosion. Therefore, the engineers should accurately predict and prevent the propagation stage start. The literature describes several models for evaluating the end of the initiation stage. However, few of them applies the Boundary Element Method (BEM) for this purpose, despite its known accuracy. Besides, enormous randomness affect the phenomenon. Thus, it is adequately handled solely in the probabilistic context. Optimisation techniques may be coupled in the problem modelling to propose adequate cover thickness values accounting for probabilities of failure. This study presents a Reliability-Based Design Optimisation (RBDO) approach for designing accurately the cover thickness of concrete structures subjected to chloride ingress. The BEM handles the diffusion modelling whereas the Monte Carlo simulation assesses the probabilities of failure. The RBDO is formulated in the context of Weighted Average Simulation Method (WASM), which requires only one assessment of the reliability analysis. It leads to a reliable and computationally efficient solution technique. The problem formulation and the implemented solution scheme are described herein. Moreover, one application is presented, in which the design results are interpreted properly.

Probabilistic chloride diffusion modelling in cracked concrete structures by transient BEM formulation

“…Yang et al [26], [27] adopted it for the diffusion modelling of chloride ions into cover thickness of concrete structures, and Chen et al [28] analysed chloride diffusion in high-performance concretes, in which the BEM performance was compared against experimental results. Pellizzer and Leonel [29] modelled chloride ingress in concrete pores using the time-dependent BEM approach for diffusion, and later [30] proposed a Reliability-Based Design Optimisation (RBDO) formulation for the probabilistic optimisation of cover thickness in concrete structures subjected to chloride penetration. The present study contributes to the field applying the transient BEM approach for the time-dependent diffusion modelling of chlorides in concrete structures.…”

“…Nevertheless, the computational effectiveness of BEM enables a probabilistic description via MCS. Very few studies have adopted this coupling scheme [29], [30], [34], thus motivating this research, which deals with the probabilistic modelling of chloride ingress in concrete pores.…”