Numerical simulation of plate anchors under combined translational and torsional undrained loading
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Plate anchors are increasingly being used to moor large fl oating offshore structures in deep and ultradeep water. These facilities impart substantial vertical uplift loading to plate anchors. However, in extreme operating conditions hurricane loading often results in partial system failures, with signifi cant change in the orientation of the remaining intact mooring lines. The purpose of this study is to investigate the undrained pure translational (parallel to plate) and torsional bearing capacity of anchor plates idealized as square and rectangular shaped plates together with the interaction response under combined loading using three-dimensional fi nite element (FE) analysis. In order to avoid adverse effect of unrealistic stress distribution on the corners of especially deeply embedded plate, interfaces are defi ned near the sharp edges of the thin plate to accommodate the velocity discontinuities near the tip of the anchor plate. Upper bound plastic limit analysis is employed to establish a reference value for torsional and translational bearing capacity, and an interaction relationship for the combined loading condition. The results of plastic limit analysis (PLA) solution showed a satisfactory agreement with fi nite element results. Interaction relationships developed from the numerical and analytical studies are fi tted to a simple two degree-of-freedom yield locus equation which can be used as an associated plastic failure locus for combined shear and torsional loading to predict the plastic displacements in the translational and torsional directions.
