Finite-element-based system reliability analysis and updating of fatigue-induced sequential failures

Lee, Young Joo

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https://hdl.handle.net/2142/30920 Copy

Description

Title

Finite-element-based system reliability analysis and updating of fatigue-induced sequential failures

Author(s)

Lee, Young Joo

Issue Date

2012-05-22T00:15:14Z

Director of Research (if dissertation) or Advisor (if thesis)

Song, Junho

Doctoral Committee Chair(s)

Song, Junho

Committee Member(s)

• Spencer, Billie F., Jr.
• Masud, Arif
• Millwater, Harry R.

Department of Study

Civil & Environmental Eng

Discipline

Civil Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Finite element
• System reliability
• Reliability updating
• Fatigue
• Sequential Failure
• Branch-and-bound
• B3 method
• Structural inspection

Abstract

Fatigue is one of the main causes of structural failure. In fact, many structural systems such as bridges, offshore platforms, and aircraft are subjected to the risk of fatigue-induced failure caused by repeated loading over their life cycle. Therefore, structural systems should be designed and maintained such that they have an adequate level of structural redundancy to prevent local fatigue-induced failures from progressing toward system-level failure such as collapse, which may result in complete loss of the structural system and catastrophic consequences. For decision-making with respect to the design, maintenance and retrofit of robust structural systems, it is thus essential to estimate their reliability and identify critical sequences of local failures leading to system failures. In addition, it is desirable to update the original reliability based on inspection results, which will facilitate reliability-based structural maintenance based on the actual conditions of structures. Performing reliability analysis and updating of fatigue-induced sequential failure of a structural system is a challenging task. First, the reliability analysis should be performed at the system level in conjunction with sophisticated finite element analysis to account for the complex behavior of the structure during fatigue-induced sequential failures including the impact of load re-distribution caused by failures at other locations. Second, one might need to explore a huge number of failure sequences to estimate the failure risk accurately, especially for complex structural systems with high level of redundancy. Third, for accurate system reliability updating, precise system reliability estimation should be performed first and then the results should be incorporated into a method that can update the original reliability based on inspection results. This thesis proposes novel finite-element-based methods for system reliability analysis and updating for structures that are subject to the risk of fatigue-induced sequential failures. First of all, a new computational framework is developed which performs finite element reliability analysis (FE-RA) at the system level. While many of the existing FE-RA software packages aim at reliability analysis at the component level or have the limited capability of their FE modules, the new framework enables us to perform system reliability analysis in conjunction with sophisticated finite element analysis. Secondly, a new Branch-and Bound method employing system reliability Bounds (termed the B3 method) is developed to perform system reliability analysis for the fatigue-induced sequential failures of structures. Describing sequential failures as disjoint events, the B3 method enables us to estimate the system-level failure probability and identify critical failure sequences, more accurately and efficiently than other existing methods. The B3 method was originally developed for reliability analysis of discrete structures such as a truss, but the method is further developed for its applications to continuum structures. Lastly, a new reliability updating method employing the B3 method is proposed to update the system reliability analysis results based on structural inspections. The approach can update the original failure probability of structures based on various conditions observed during inspections for both truss and continuum structures. All of the proposed methods are applied to numerical examples of structural systems, and the results are compared with those by Monte Carlo simulations, which show that the proposed methods can perform system reliability analysis and updating in conjunction with finite element analysis, accurately and efficiently.

Graduation Semester

2012-05

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http://hdl.handle.net/2142/30920

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Copyright 2012 Young Joo Lee

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