Effects and Analysis of Crane Boom Impact Damage for Offshore Cranes
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Cranes are important constructions on offshore installations. Offshore cranes with latticed boom are exposed for unwanted collision with other objects, damaging the load-carrying structure. This thesis targets to detect the important parameters of such impact damage, and how they effect the capacity of the crane. The geometry and dimensions of Wolffcran's HDK 1000 HM crane is used as basis for a finite element (FE) model of a latticed boom. The crane boom is modelled and analysed in the FE program, Abaqus. Relevant crane loads are identified and established for different lifting radii. This includes loads from two different hoisting systems, wind, and sidelead load caused by sideways displacement of the load on the supply vessel deck due to motion of the vessel. The capacity of the crane boom is determined from the buckling load of nonlinear buckling analyses. A parametric study of damage of one of the bracing members of the boom are conducted, including the parameters; indentation depth of dent, radius of impact object, deflection of bracing and location of damage. The indentation depth of the dent and the deflection of the member were found as the parameters with highest influence on the buckling load. Further, global analyses of the crane boom are performed. Impact damage, with various grade of indentation depth and deflection were analysed at different locations of the crane boom, with different lifting radii. The most critical location of the damage was found to be at the main girders at the back of the boom. Damages at other locations of the boom were surprisingly insignificant for the buckling load. An empirical formula is developed to determine the reduction in SWL (Safe Working Load) due to damage. The formula is developed to fit the numerical results of damage at the main girders at the back of the boom. The formula is accurate for small damages and is gradually more conservative for larger damages. This due to the unknown fatigue effect, which is not analysed in this thesis.