Keywords: operation lifetime extension, risk analysis, quality assurance process, numerical simulations, aircraft crash.

In many industrial sectors, owners study how to extend the working lifetime of strategic ageing facilities and more particularly reinforced and prestressed concrete civil engineering works. The decision to extend the operation of civil engineering works requires making a diagnosis of the current state and a prognosis of future changes (related to the operation conditions, the regulatory requirements, the environment, etc.). A risk analysis may be the solution to manage such an issue. Indeed, a risk analysis identifies the structure weaknesses by ranking the failure modes according to the probability of occurrence (frequency) and a level of consequences (severity). For this, numerical simulations are useful, even necessary, to assess some complex phenomena such as the global mechanical behaviour of a structure subjected to a aircraft crash.

However, if the risk analysis is performed in the generic process of quality assurance, the use of simulations should also be realized according to an equivalent methodology. Such a methodology aims at ensuring the owner's needs are satisfied and helping the engineering works in spite of the project constraints (time, costs, etc.). In particular, the two main principles of the methodology are:

1. identifying the model assumptions (and limitations) for the structure, static operating loads and dynamic crash accidental loads and
2. estimating the model precision (complexity) that should be necessary and sufficient to answer questions.

Such a methodology has been implemented during a main risk analysis applied to an existing prestressed and reinforced concrete cylindrical structure. The risk analysis has highlighted that the characteristics of the civil aviation fleet (cabin diameter, wingspan, payload) have been increasing since the design and commissioning of the structure. In other words, it is likely that a bigger and larger aircraft than one considered during the design may crash on the structure. Therefore, numerical simulations are performed with the ABAQUS (explicit dynamic solver) in order to analyze the consequences of new scenarios of aircraft crash on different parts of the structure. Then, the direct results of the numerical simulations are analysed to evaluate the crash effects on the three main functions of the structure: "gas confinement", "global mechanical stability" and "local mechanical strength". Finally, the results contribute to the risk analysis to compare the event of the aircraft crash with others about operating or accidental events (earthquake) and help owners to make relevant and resonate decisions.

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