Int. J. Reliability and Safety, Vol. 1, Nos. 1/2, 2006 137 Copyright © 2006 Inderscience Enterprises Ltd. Efficient first-order reliability analysis of multidisciplinary systems Sankaran Mahadevan* and Natasha Smith Department of Civil and Environmental Engineering, Vanderbilt University, Box 1831-B, Nashville, TN 37235, USA E-mail: sankaran.mahadevan@vanderbilt.edu E-mail: Natasha.l.smith@vanderbilt.edu *Corresponding author Abstract: This paper develops two algorithms that address the reliability evaluation of complex multidisciplinary engineering systems. In particular, systems with feedback coupling – a common characteristic of many multidisciplinary analyses – are considered. In such analyses, iterative convergence loops are needed to resolve inconsistencies in feedback variables. Assessing the reliability of such systems with a traditional ‘black box’ or fully coupled approach requires Multidisciplinary Analysis (MDA) convergence loops nested inside iterative loops for probabilistic analysis. The resulting computational effort is unacceptable for most high fidelity analyses. Therefore, this paper proposes two first-order reliability analysis methods that efficiently apply probabilistic analysis to multidisciplinary systems with feedback using a decoupling approach. The first method uses a First-Order Second Moment (FOSM) technique to characterise intermediate variables while applying more rigorous reliability analysis on the system as a whole. The second algorithm gives a specific solution to a decoupled first-order reliability analysis formulation as an optimisation problem. Each method is applied to an illustrative mathematical model and compared to otherwise equivalent coupled approaches with respect to accuracy and computational effort. Keywords: Multidisciplinary Analysis (MDA); optimisation; probabilistic methods; reliability analysis; coupled systems; decoupling. Reference to this paper should be made as follows: Mahadevan, S. and Smith, N. (2006) ‘Efficient first-order reliability analysis of multidisciplinary systems’, Int. J. Reliability and Safety, Vol. 1, Nos. 1/2, pp.137–154. Biographical notes: Prof. Sankaran Mahadevan is the Director of Vanderbilt University’s NSF-funded multidisciplinary graduate programme in Reliability and Risk Engineering and Management. He received his PhD in 1988 from Georgia Institute of Technology. His research contributions are in model-based simulation, mechanical systems durability, reliability and risk assessment, design optimisation and model validation techniques, with applications to civil infrastructure, automotive and aerospace systems. His research has been funded by NASA, DOD, DOE, NSF, GM, DaimlerChrysler, Union Pacific and Oak Ridge, Sandia and Idaho National Laboratories. His research is documented in more than 200 publications. Natasha Smith is a PhD candidate and an NSF-IGERT fellow in Vanderbilt University’s multidisciplinary graduate programme in Reliability and Risk Engineering and Management. Her dissertation research has focused on reliability-based design of multidisciplinary systems.