Astra 3.0: Logical and Probabilistic Analysis Methods

This report contains the description of the main methods, implemented in ASTRA 3.0, to analyse coherent andnon-coherent fault trees. ASTRA 3.0 is fully based on the Binary Decision Diagrams (BDD) approach. In thecase of non-coherent fault trees ASTRA 3.0 dynamically assigns to each node of the graph a label that identifiesthe type of the associated variable in order to drive the application of the most suitable analysis algorithms. Theresulting BDD is referred to as Labelled BDD (LBDD). Exact values of the unavailability, expected number offailure and repair are calculated; the unreliability upper bound is automatically determined under givenconditions. Five different importance measures of basic events are also provided. From the LBDD a ZBDDembedding all the MCS is obtained from which a subset of Significant Minimal Cut Sets (SMCS) is determinedthrough the application of the cut-off techniques.With very complex trees it may happen that the working memory is not sufficient to store the large LBDDstructure. In these cases ASTRA 3.0 performes the analysis by constructing a Reduced ZBDD embedding theSMCS using cut-off techniques thus by-passing the construction of the LBDD.The report also contains three short tutorials on the BDD approach, on the usefulness of non-coherent faulttrees and on the determination of failure and repair frequencies. How to obtain EU publications Our priced publications are available from EU Bookshop (http://bookshop.europa.eu), where you can placean order with the sales agent of your choice.The Publications Office has a worldwide network of sales agents. You can obtain their contact details bysending a fax to (352) 29 29-42758. The mission of the JRC is to provide customer-driven scientific and technical supportfor the conception, development, implementation and monitoring of EU policies. As aservice of the European Commission, the JRC functions as a reference centre ofscience and technology for the Union. Close to the policy-making process, it servesthe common interest of the Member States, while being independent of specialinterests, whether private or national.LB-NA-2452-EN-C