An international benchmark has been organized by EDF R&D during 2008–2010, gathering 11 partners. Its main objective is to quantify the confidence in numericalmodels. The built-up dynamical system considered is a pump actually in service in powerplants, considered in its work environment. Blind eigenfrequency numerical values relativeto the pump assembly fixed in concrete present a larger variability than the 5% roughvariability concerning the separate parts, essentially due to the modeling of the boundaryconditions and interfaces at macro level. For the nine first eigenmodes considered, experimental-numerical correlation shows a frequency error less than 15% for the freesub-structures and nearly 30% for the free five-component system. Though the first overallmodes are correctly identified, the frequency error is significantly larger for theclamped pump assembly, with however MAC coefficients higher than 0.9 for two modes; butthe frequency error can be reduced to less than 9% for the four first modes after updatingprocedure. A lesson to draw is that measurement information is needed to improve thequality of theoretical built-up structure. After this benchmark, a more ambitious researchprogram will follow as a FUI project, gathering the observation of numerical andexperimental variabilities, updating model improvement and numerical quantification of thetotal uncertainty.