Stochastic finite element methods for reliability analysis of deteriorating structures and infrastructures
Creators: name: Seyfallahi Asl, Alireza
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 400510
subject: Structural engineering

description: Finite element method (FEM) has been widely used for modeling the structures subjected to various loading conditions. However, it is a challenging task to model a deteriorating structure in presence of cyclic loadings (i.e., fatigue), using FEM. Additionally, considering the uncertain nature of degradation processes (such as corrosion) in FEM, requires the application of stochastic approaches instead of widely used deterministic approaches. This study aims at addressing the aforementioned issues by incorporating the stochastic degradation models and also the reliability analysis methods into the FEM, in order to provide an accurate failure analysis of corrosion affected steel structures and infrastructures such as rails and/or steel bridges. The study also investigates the impact of corrosion on micro mechanical properties of corroding steel. The outcome of the research is expected to provide a stochastic FEM approach to accurately analyze the reliability of steel elements subject to corrosion and fatigue. The application of the developed model will be validated on bridge steel girders as well as rails.

This research will concentrate on studies that look at corrosion effects on steel structures at multiple scales. Over the last few decades, many numerical studies have been conducted to assess the corrosion effects on steel structures. This research will discuss numerical studies that have used FEM to assess the mechanical properties of mild steel.

This research critically examines existing methods for structural analysis of steel structures under corrosion, fatigue, and a combination of corrosion and fatigue that is used to estimate service life. The corrosion rate and its impact on the properties of mild steel will also be discussed. Experiments will also be carried out to detect the corrosion impact on the mechanical properties and microstructural features of mild steel.

The methodology and techniques for simulating steel structures at the micro and macro levels will be covered in this research. These methods combine numerical and experimental research to create an accurate model for simulating steel structures. The methodology is developed to fill gaps in the literature review, such as assessing the process of mechanical property deterioration of mild steel due to corrosion at both the macro and micro levels. Based on a real-world case study, the FEM method was also used to simulate the combined effect of fatigue and corrosion on mild steel at the micro and macro levels.
The experimental tests in this research are designed to investigate the micromechanical properties of corroded steel. The results of the tests are then used to create the numerical model with FEM.

Nanoindentation and EBSD mapping tests are used to investigate the micromechanical properties and morphology of corroded steel elements. 
This research has been able to develop a numerical model using stochastic FEM which can accurately predict the mechanical behaviour of mild steel at the micro scale. The effect of corrosion on the micro mechanical properties of mild steel has been provided. The reliability analysis for both structures (rail and bridge) has been carried out as well.