The Safety Assessment Of Offshore Platform's Jacket Structure

The jacket platform,also called pile supported platform,is a typical stationary platform.It is supported by the piles extended into the seabed,which differentiates it from other kinds of platform.Since the jacket platform is characterized by its complex structure and valuable construction cost and it always suffers from ocean environment loads,it is an effective way to save cost by prolonging its service life.Therefore,safety assessment of the jacket structure is essential for security."The method of safety assessment of the jacket structure is discussed from the perspectives of certainty assessment and reliability assessment,based on the software SACS.The main work is as following:(1)The load theory adopted in calculation is introduced,and the Morison equation and wave theory are analyzed highlighted.The jacket platform model is developed.The pile and soil interaction theory and structural damage correction method,used for restriction condition treatment,are discussed in details.(2)The static forces of the jacket structure are calculated based on the software SACS.The static strength in eight main directions of load is checked.The stress ratio of components is calculated,followed by component certainty assessment and system certainty assessment of the model.The process of system certainty assessment based on analytical hierarchy process is elaborated.The key issues of numerical simulation and naming rule of the model is discussed.The analysis and assessment of Service conditions of the model is developed,according to the certainty assessment.(3)The ultimate bearing capacity of the model is analyzed.The principle of collapse analysis in the software SACS is discussed.The ultimate bearing capacity of the model in several directions of load is numerical simulated,followed by analysis of collapse process,comparison of ultimate bearing capacity and collapse characteristics in different directions.(4)Combined with the numerical results of collapse and reliability theory,the system certainty assessment of the model is developed.The fitting process of load equivalent formula is discussed,which takes into account the randomness of ocean environment loads(wind,waves and currents),followed by fitting of load equivalent formula in different directions.The checking point method for reliability problem is discussed.The reliability calculation formula is given.The system certainty assessment and failure probability in different directions of the model is predicted,followed by discussion of the results.