The Study Of Oil Derrick Ultimate Bearing Capacity

Oil derrick is an important part of oil equipment. For many years, some accidents of derrick collapse have happened occasionally, only according to the elastic theory to evaluate can't meet the need of oil field derrick work fully. Therefore, forecasting the ultimate bearing capacity properly has become an urgent content of safety evaluation theory.As the most frequently employed method is to determine the load resisting capacity by the method of the linearity extrapolation from the measured data about stress, thus this paper present the ultimate bearing capacity method based on the measured stress of derrick members to modify the computer numerical model, which realized the unification on algorithmic analysis and continuity on theory between safety evaluation and ultimate bearing capacity forecasting.This paper firstly analyzed the geometric and material nonlinearity according to FEM method. After it, it established the numerical model of perfect derrick by using huge engineering auxiliary software-ANSYS, and analyzed the influence of geometric nonlinearity on the parameters of derrick; In addition, this part discussed the geometric and double nonlinear ultimate bearing capacity aiming at numerical model and concluded that double nonlinearity must be considered if you want to acquire the ultimate bearing capacity of A-shaped mast.This thesis combined not only the theory analysis of derrick structure and measured data but also test in Lab and test in oil field. Further more, this research has adopt mass parallel real-time test system with 64 channels, DAQ data acquisition panel with PCI wire, Labview software and DASYlab analysis platform. We gathered and analyzed data of Lab model and derrick in oil field and then offered enough and accurate data for forecasting ultimate bearing capacity.Finally, according to the research above, the author presented the method, with which we can forecast the ultimate bearing capacity of derrick with defeats and defacements by modifying the perfect numerical derrick model with the method of taking measured stress as reference. This method could achieve excellent solution, but we must modify each element of FEM numerical model and then the amount of work is very large. Therefore practically the author took the measured stress of derrick members as reference to infer the ultimate bearing capacity. The relative error is only 5% between the forecasting result of Lab model and the result of collapsing test, which also proved that it is a feasible.