Different types of structures submitted to thermal loadings under different conditions of support are studied in this work, with the purpose of analysing the thermal Ratchet Mechanism. This phenomena is na important criteria of safety of nuclear power systems. A first model was used to simulate the bahavior of a structure free of bending, submitted to temperature fluctuation. The conditions for Ratcheting are determined. A second model was used to simulate the behavior of two tubes joinned at theirs ends, and submitted to a linear profile of temperature in its cross-section. A third model was used to beams on elastic foundation. This may be used to simulate the behavior of a cilindrical vessels submitted to thermal loadings.