Study on direct updating theory for derrick steel structures with damage and defacements

Several damage and defacements widely existing in derrick steel structures are divided into local and overall damage and defacements. Local damage and defacements include cross-section corrosion, member bar initial flexure and the nodes stiffness reducing. The overall damage defacements include overall initial flexure, loading eccentricity and support subsidence. The corresponding damage correction functions are respectively derived. Revising the finite element model directly by these functions, the numerical model tending to real structure can be obtained. Measurement for damage and defacements and dynamic load stress test are conducted on in-service derrick steel structure. The corrosion thickness of member bars, the initial flexural deformation of the rods, the overall initial flexure, the loading eccentricity and support subsidence are measured. Direct updating theory is used to revise the finite element model, and safety assessment for the in-service derrick steel structure is carried on. The results show that the derrick steel structure with damage and defacements can not meet the original design requirements and the actual bearing capacity decreases. The results provide a valuable reference for the safety operation of the in-service derrick steel structure.