In order to analyze the stability of structures or structural components, it is usually necessary to determine imperfections. Basically, a distinction is made between the geometric and the structural imperfections.
The geometric (external) imperfections are deviations from the planned geometry caused by the production or assembly. These can be, for example, unplanned load eccentricities, precamber of the member axis, or member sway imperfection.
The structural (internal) imperfections are also caused by the production and consider the internal stresses or an uneven distribution of the yield strength over a cross-section, for example.
Usage in Program
Imperfection cases allow you to define the general conditions of imperfections, that is, whether they should be considered as geometric pre-deformations, equivalent loads, or a sway imperfections by story.
Generally, the following imperfection types are available for selection in the program:
- Local Imperfections Only:
The imperfections are applied as equivalent loads; the initial sway and the initial bow depend on axial forces.
- Notional Loads from Load Case:
The imperfections are based on the loads of a load case.
- Initial Sway via Table:
The imperfections are represented by story.
- Static Deformation:
The imperfections are based on the deformations of a load case or a load combination.
- Group of Imperfection Cases:
The specifications of several imperfection cases are combined.
Each imperfection case can then be assigned to specific load cases or combinations.