Study On Failure Mechanism And Risk Assessment For Offshore Jacket Platform Under Fire Effect

Assessment-based on global structure under fire effect is an important trend for fire-resistance research of steel structures. Compared with that based on member, the anti-fire design method based on global structure can help us to save much more steel material and construction cost by utilizing the structural interaction effect between members more effectively, and making use of the potential fire-resistance ability of steel. In order to investigate the total fire-resistance capability of steel buildings, an offshore jacket platform of BZ28-1 in Bohai Bay is applied to carry out global structural response analysis under compartment fire effect in this dissertation.The fire combustion analysis is a basic one for global structure fire resistance research. Fire characteristic and its condition for ignition and development are illustrated. Concerned with fire hazard on platform, the specialties different from that of general fire, the inflammable matters and the classification of firing source are presented, and the gradation, as well as importance for anti-fire design is pointed out.Then, the global structural temperature and response of offshore jacket platform under fire effect are analyzed. Based on the law of energy conversation, Fourier heat transfer law and Newton cooling equation, a mathematic model for temperature distribution analysis of offshore jacket platform under fire effect is established to solve the real case, BZ28-1 offshore jacket platform, under fire effect. At the same time, a transient calculation FEA model for global structural temperature of real case is established to compare with the mathematic model. After obtaining analysis results, deduce the equation to calculate the equivalent mean temperature of steel structures under fire effect. A transient calculation FEA model for response analysis of offshore jacket platform is gotten out in order to get the variable stresses and displacements with temperature under determined loads. In this model, nonlinear strain-stress curve of steel with the increment of temperature is used by the elastic-plastic method. On the basis of analysis, summarize the collapse and failure mechanism for offshore jacket platform under fire effect. Furthermore, a preliminary theory of global structural failure for offshore jacket platform without protection, and the classification of its failure stages are put forward.In addition, fire risk assessment and preventive measures for offshore jacket platform are discussed. The BFSEM risk assessment method is adopted to make quantitative risk assessment for offshore jacket platform, which can reduce the demand for fire datum and has its real sense to some extent. Meanwhile, aimed at offshore jacket platform, seven practicable and comprehensive fire preventive measures are brought out, which can reduce the fire incidence rate, protect properties and insure safety of human beings.Finally, some proposals of fire-resistance design for steel structures are presented, which, hopefully, will be useful for further study.