Initial Shape
For thin-walled cross-sections with material Aluminium the Initial Shape is generated automatically.
For a General cross-section the ‘Thin-walled representation’ has to be used to be able to define the Initial Shape.
The Initial Shape 'translates' the cross-section shape to parts defined by the code.
The Initial Shape is used for calculating the effective section properties as well as determining the Classification of the cross-section.
The thin-walled cross-section parts can have the following types:
|
F |
Fixed Part – No reduction is needed |
|
I |
Internal cross-section part |
|
SO |
Symmetrical Outstand |
|
UO |
Unsymmetrical Outstand |
Parts can also be specified as reinforcement:
|
None |
Not considered as reinforcement |
|
RUO |
Reinforced Unsymmetrical Outstand (edge stiffener) |
|
RI |
Reinforced Intermediate (intermediate stiffener) |
ROU reinforcement types can be set only to elements of type SO or UO.
RI types can be set only to elements of type I or UO or SO.
For general cross-sections neighbouring elements of type RI are seen as one stiffener for the calculation of the stiffener area and inertia.
For standard profile library cross-sections, the flat parts are taken between the roundings. The roundings are set as fixed parts.
For predefined sections without roundings, the initial shape is based on the centreline dimensions i.e. the flat parts are taken between the intersection points of the centrelines.
Initial Shapes for specific sections
Within this paragraph special cases for the Initial Shape generation are listed.
Sheet welded Iw & Iwn
For these sections the weldsize is accounted for in the generation of the Initial Shape:
The length of the web element for example is thus calculated as:
With Hw the height of the web and a the throat thickness of the weld.
The same approach is used for the flanges.
RHS
For Rectangular Hollow Sections (FC 2) the initial shape is generated using a notional width of h-3t and b-3t.
The usage of this width is the same as in steel in which it ensures consistency between EN 1993-1-1 and EN 1993-1-5. For further information reference is made to Ref.[3].