PhD ThesisThe Simplified Progressive Collapse Method is a quick and well‐established method
recommended by International Association of Classification Societies (IACS) for the evaluation
of a ship’s ultimate strength due to longitudinal bending. However, in the case which the
torsional rigidity of the structure is reduced i.e. containerships, longitudinal bending may not
be the dominant reason for failure. Torsion and shear forces may influence the global strength
and therefore the effect of combined loading needs to be investigated.
The current research aims to understand hull girder failure modes under these combined
loads both for intact and damage case scenarios and incorporate torsional loading effect into
the existing method. A hull girder which is subjected to longitudinal bending moment and
torsional loading generates compressive/tensile and shear stresses on its plates and stiffened
panels. Therefore, a thorough investigation of plates under these combined loads has been
carried out. The outcome of this study is interaction diagrams of compression/tension and
shear for steel and aluminium plates. The ultimate strength of the structure is then estimated
for an applied amount of torsion calculating the shear flow distribution of the plates in the
cross section and using the results of the previous study. The same procedure is repeated for
different amounts of torsion and the interaction diagram of vertical/horizontal bending
moment and torsional moment is derived.
For validation, the proposed method is applied to a number of different intact box girders and
to a hull girder of a 10000 TEU containership. The effect of damage on the ultimate strength
is examined only under bending due to the current representation of damage in the simplified
method. The results are compared with the results of non‐linear finite element models which
have been generated and analysed for this purpose.
The results for all studies show very good correlation, however the simplified method provides
a sufficient advantage of time estimation and simplicity in comparison with the existing
methods. It can be used in both concept and preliminary design to provide accurate estimation
of hull girder strength. This extension of the Simplified Progressive Collapse Method, which
accounts for combined load effects, is particularly useful in cases which require quick estimate
of ultimate strength.Office of Naval Researc