From the analysis results, we must control if the designed structure will have sufficient capacity to
maintain strucural integrity and avoid collapse or failure. The following design criterias
are important for the structural analysis:
Yielding (e.g. defined by the von Mises criterion)
We reach this state when the stress in the metal exceeds the yield stress.
When the metal yields, it changes behaviour from elastic to plastic. We will here loose
much of the capacity, and yielding should of course be avoided. Some yielding are
of course unavoidable, such as in weldings.
Buckling is a state that shells or trusses reach when pressure loaded upto a certain
critical stress. The component then buckles out and loses much or all of its capacity.
This again, can lead to a total collapse of the entire structure. Buckling is an important
problem in ships and offshore structures.
Fatigue is a dynamic problem. The problem can arise when we have alternating loads. After a certain amount of load cycles, cracking will occur,
and we can have structural damage. The amount of cycles needed before cracking is dependent
of the magnitude and frequency of the alternating load conditions.