| The bearing capacity of oil derrick will decrease because of the working condition and movement, as stated in national standard that need to detect it. But in present test process only set sensors in the section of low position of derrick because it is so high and workers are dangerous to clumber to the higher position. If we made evaluation used these data it bring with error on the grounds of the data that not tested at the most dangerous and maximum capacity position for derrick.In order to establish a equal simulate model for in-service oil derrick, probe the load secrets of influences when it contained some initial defects and improve the precision of stress and damaged data between testing and simulate derrick, then get the bearing capacity. This paper depend on theory of finite element analysis, got the no damage defects derrick stress distribution under load through establishing and analysis the calculation model derrick At the same time, a model updating method based on Force analysis of K derrick was made with initial defects such as corrosion and bending of local bar, the bending of whole derrick legs, substructure settlement was presented that mean square deviation of testing and simulate derrick stress were taken as optimal objective function; damage deficiencies type, position and grade were defined as design variables; material allowable stress were set as state variables; ANSYS Zero-order and First-order theories were used in the process of optimization. This method was used to the analysis of damaged simulate and testing derrick, after the model updated, contrasted with the extracted stress data from truss members between these models, we can inferred that the relative error was about 10%, that means this method is feasible and effective for the evaluation of rig derrick bearing capacity, in additional, based on the conclusion of this paper we inferred that it maybe a suggestion to rig machinery safe in operation.
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