This research was undertaken with the aid of the considerable amount of data and measurement gathered by ENEL (Italian Electricity Board) during the construction and operation of some of its power plants. The study also aims at evaluating how the predictions, based on some currently available calculation methods, relate to the actual behaviour of such structures, by giving an a posteriori evaluation of the reliability of these methods. The structural characteristics of power plant buildings can be described by rigid, flexible or intermediate interaction models. The research includes the geo-technical characterization of foundation soils and settlement analysis by means of 2-D and 3-D models. Comparison between calculation results and the large amount of settlement measurements allowed both the evaluation of the degree of reliability of the methodologies presented, when applied to design, as well as, the identification of those factors which mainly affect the correct prediction of building behaviour versus time.