Thermal Dynamic Analysis Of Typical Offshore Structures Subjected To Elevated Temperature

Offshore structures,such as offshore platforms,have potential fire hazard due to the tough manufacturing environment and high density of oil and gas equipment,hence there is a need to have a structure safety assessment when exposed to fire accident.Besides,although steel is widely used in ships and ocean structures,the poor behavior of steel in fire still remains a big restraint for further use.Under this circumstance,research on the fire-resistant performance of steel is gaining more attention than before,with great engineering significance.Some issues are discussed and studied in this thesis,with numerical simulation method,including thermal dynamic response of large-scale ocean structures,fire resistances of structures protecting by coatings,structural design of individual member under elevated temperatures.The main contents are listed as follows:In terms of thermal dynamic response of large-scale structures,disadvantages of traditional static analysis were pointed out.The thesis adopted fully coupled explicit dynamic analysis as solver,which was validated with experiment results in advance,and made a full analysis of some large-scale grillage structure encountering fire.Global progressive collapse of structure was traced in this way.The research shows that plate thickness and boundary condition play important roles in grillage structure's mechanical response.An excessive boundary restraint will cause extra axial thermal tress and local buckling,while on the other hand provide sufficient support for lateral loads.Members with insufficient boundary restraint are not inclined to buckle,but will have large displacements under fire conditions;As for structures protecting by fireproof coating,a new method based on composite shell elements was proposed and compared with brick elements and experiment results,to show its advantage of high accuracy and efficiency.Based on this method,thermal and mechanical response of the same grillage structure protecting by coatings were analyzed.The result showed that intumescent coating can significantly delay temperature rising within structure,and reduce the global dynamic effect due to thermal load;In the current design of structure in fire,complicated high temperature environments were not fully taken into account.In this thesis,ultimate shear resistances are computed by nonlinear arc-length method and validated with experiment results.Aiming at non-uniform temperature situations,this thesis considered there different temperature distributions and detailed the inadequacy of Eurocode 3.Based on discussion,an improved method to predict the shear resistance of steel plate girder at non-uniform elevated temperatures is presented.Furthermore,situations where axial restraints exist are considered.An applicability study is done on shear-compression interaction formula recommended by Eurocode 3 for this condition.The results show that this formula is on the safe side when shear load ratio is relatively high,but unsafe when ratio is low.In conclusion,the research in this thesis and relative conclusions can provide references for the further study on numerical analysis method and failure mechanism of thermal dynamic response of large structures,also for the design of structure in fire.