The Structural Safety Assessment Of Jacket Platforms In Liaodong Bay

With the development of economic, the demand for energy increases gradually. With the increase in the exploitation of offshore oil and gas resources, offshore platforms become important offshore structures. The jacket platform is very expensive while its service environment is very bad and complex. The consequences of structural failure are greatly serious. Hence the structural safety assessment has become an important problem to ensure the development of offshore oil and gas resources in security. The structural safety assessment can be divided into two-levels: structural members and integral structure. As the large-scale structure itself has a high redundancy, in some cases, part structural members do not meet safety requirements while the structure maybe run as usual. Therefore the structural safety assessment of jacket platforms is more focused on security situation of the whole platform. Combined with the large-scale finite element software ANSYS to model and analyze the jacket platform, and it is used two methods of the definitive and reliability assessment to carry out structural safety assessment. In order to ensure the accuracy of modeling and loading and the credibility of the results, the author investigates and collates the information of marine environment around the jacket platform, and masters the structural characteristics of jacket platforms.In this dissertation, the methods and steps of structural safety assessment of jacket platforms are given, and failure modes and discrimination index of offshore platforms under the influence of sea ice are analyzed, and the method of using the systematic risk calculation formula given by Pate-Cornell to calculate system failure probability as well as the method of considering three aspects of life loss, property damage and environment destruction to analyze failure consequence are introduced.In addition, the definitive assessment of the jacket platform mainly compares the results with the specifications to check whether the results is permitted. The results of static analysis show that the maximum displacement and equivalent stress of the structure are within the requirements of the specification under the extremal static ice force, therefore the platform has a large static emergency capacity. The results of modal analysis show that the vibration period of the structure is far less than the external environment's, therefore, resonance phenomenon does not happen. The results of transient analysis show that the displacement of the upper platform is bigger, and the stress is larger in pile diameter changes and tubular joints, therefore, these areas should be the focus of security. The reliability assessment of the jacket platform mainly analyzes the reliability of the platform in the marine environmental conditions, and the results clearly show that the platform meets the safety design requirements.