TABLE OF CONTENTS In the gross plastic deformation design check (GPD-DC) and the progressive plastic deformation design check (PD-DC) the design models used give confidence in results the results for well-posed problems are unique, they are fairly insensitive to initial residual stresses, initial geometric imperfections, material inhomogeneities, action histories and to perturbations of action values, and quite often they are even independent of these disturbances.
Additionally, in the PD-DC the underlying failure mode is not related to a sudden failure in a single application of an action, but with progressing deformation due to cyclic actions, allowing the timely detection of failure by appropriate in-service inspections.
In the S-DC, discussed in this chapter, this confidence cushion does not exist non-uniqueness is an essential feature of this design check and the used design models, and imperfection sensitivity as well as sensitivity to initial residual stresses to the action histories is a quite frequent property of real structures and of design models.
To reflect the behaviour of real structures appropriately, models with non-linear kinematic relations and second-order-theory are required. The second requirement, the obligation to apply second-order-theory, i.e. equilibrium conditions for the deformed structure, leads to another feature of the models not encountered in first-order theory models: Pressure is displacement dependent, and it acts normal to the surfaces of structures. In second-order-theory models, pressure is normal to the deformed surfaces, and its value may also depend on displacements. This can decrease results for critical pressures in the stability checks quite considerably, compared...
