A re-evaluation of the hull girder shakedown limit states

This paper investigates the use of shakedown limit state in the assessment of longitudinal strength of ship hull girders. This consideration is related to the fact that a structural system subjected to cyclic loadings may suffer from plastic collapse even when the loading magnitude is less than the instantaneous collapse load of single excursion. This paper first evaluates the shakedown limit state of a box girder model with and without the consideration of buckling. Nonlinear finite element analyses are also performed to investigate the structural behaviours of a case study model under six different cyclic loading protocols. The rationality of a shakedown limit state is discussed and an energy-based characterisation of limit state is suggested. The study shows that, whilst the use of shakedown limit state assessment may be overly conservative, the safety margin based on an ultimate limit state approach might be considerably reduced.