Performance-based Study On Vibration-Suppression Methods For Jacket Platform And Structural Optimization

With the development of ocean energy resource exploitation, more and more plarforms are used as the basic structures on the ocean. The performances of ocean platform structures, especially the performances of offshore jacket platforms under earthquakes and other dynamic loads are having been paid more and more attention.Performance-based seismic design theory which is proposed by American scholar guarantees that structures can keep their performance levels under earthquakes in the coming days, and concernon on safety, economy and so on. Specially for ocean platforms, potential safety hazards broght by dynamic loads in the ocean are seldom considered. A targeted finite element model of CB32A jacket platform in Shengli Oil Field (Oil Field, China) is established by ANSYS program, and its dynamic characteristics are studied based on performance-based theory.This article includes the following segments:1:Based on the performance-based seismic design theory, the seismic fortification criteria for the Bohai ocean area is proposed. Failure modes, discrimination standards and performance objectives of ocean platform are proposed as well, considering structural safety, personal feelings, machine sagety and so on.2:Performance levels of CB32A platform are estimated under seismic loads (artificial wave and Tianjin wave). The numerical result shows that:Although it is safe enough for structure elements, it is dangerous for workers and machines working on the platform deck because of the excess acceleration of deck, and even lead to secondery disasters, all of which can not match performance objectives.3:Two control methods, the damping isolation layer and the TLD system, are adopted to mitigate the seismic response of CB32A platform in this paper according to its characteristics. Moreover, two different models, Housner model and simple mass point model, are adopted to imitate the storage tank above the deck considering fluid-structure interaction or not. The result shows that:Dynamic responses of the platform, not only structure element stresses but also displacements and accelerations of the deck, are effectually decreased. Especially for the the model with damping isolation system, the result of vibration-suppression is more effective than that with the TLD system, which can satisfy performance objectives proposed well. Moreover, each model of storage tank almost has the same influence on platform structure.4:Optimization is carried out with performance objectives of the platform as the restraints. Because the excessive structure redundancy is negative to build platforms in quantity in the future days for the waste of material, which obeys economic requirement in performance-based theory. The result shows a great possitive effort on material saving.