Structural analysis of an offshore steel monotubular platform ‘morena-1’ and fatigue assesment of leg-boat landing connection joint

Structural analysis of ‘MORENA-1’ platform. As a start for the work,a 3D model wa performed. Firstly, materials and sections were defined, and then assigned to the elements, then a check of dead load case was done to be sure that no design errors are involved. After the check of the design, soil properties for the foundation pile were defined also. For the soil property, two values of undrained shear strength of soil were given in the original project at z=0 at sea bottom and z=-50m, then lateral p-y curves were studied at 30 levels of 1 m space in between. After p-y curves were defined, non-linear springs that acts either on compression or on tension were also defined in SAP2000 and assigned at each node level. When the model was ready, loads and weights were defined. After load patterns were defined and assigned, load cases were defined also for each single load pattern. Where all load cases were imposed as NON-LINEAR STATIC load cases, to function properly in the NON-LINEAR STATIC ANALYSES. Load combinations were also defined according to UNI-EN-ISO-19902-2009 code. Finally, a NON-LINEAR ANALYSES was performed. The selection of NON-LINEAR ANALYSIS was based on that a monotubular platform is subjected to large deformations due to extreme conditions. As a second requirement, Fatigue of the boat landing joint under waves cyclic loading was to be evaluated. For Fatigue assessment, FEM model according DNVGL-RP-0005 was performed in SEMICENTER FEMAP WITH NASTRAN. Then, internal actions resulted from the structural analysis for each wave were inserted in FEMAP respectively, actions were applied at the same exact positions as picked from SAP2000. When all load cases were ready, a FEA analysis was performed for each case, and hot spots were tracked and listed. After the evaluation of hot spot stress, cumulative damage and fatigue life of the joint were calculated.