Structural engineers have long been trying to develop solutions using the full potential of its composite materials. At this point there is no doubt that the structural solution progress is directly related to an increase in materials science knowledge. On the other hand, the competitive trends of the world market have long been forcing structural engineers to develop minimum weight and labour cost solutions. A direct consequence of this new trend design is a considerable increase in problems

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... lated to unwanted floor vibrations. For this reason, the structural floors systems can become vulnerable to excessive vibrations, for example, produced by impacts such as mechanical equipment (rotating machinery) (Rimola, 2010; Rimola, 2010a; Rimola, 2010b). This way, the present paper investigated the dynamic behaviour of an oil production platform made of steel and located in Santos basin, São Paulo, Brazil. The structural model consists of two steel decks with a total area of 1915 m 2 (upper deck: 445 m 2 and lower deck: 1470 m 2 ), supported by vertical sections made of tubular steel members (steel jacket), and piled into the seabed. A variety of mechanical equipment was located on the steel decks of the structural model, related to electrical generators and compressors (Rimola, 2010). The soil representation was based on the Winkler's Theory (Winkler, 1867) . This theory simulates the soil behaviour as a group of independent springs, governed by the linearelastic model. In the Winkler's model, the soil stiffness was considered as the necessary pressure to produce a unitary displacement (Winkler, 1867) . The proposed computational model, developed for the oil production platform dynamic analysis, adopted the usual mesh refinement techniques present in finite element method simulations implemented in the GTSTRUDL program (GTSTRUDL, 2009). In this finite element model, floor steel girders and columns were represented by three-dimensional beam elements, where flexural and torsion effects were considered. The steel decks were represented by shell finite elements. In this investigation, it was considered that both structural elements (steel beams and steel deck plates) have total interaction with an elastic behaviour. The structural model dynamic response was determined through an analysis of its natural frequencies and peak accelerations. The results of the dynamic analysis were obtained from