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For thin-walled cross-sections with material Steel 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) |
|
DEF |
Double Edge Fold (edge stiffener) |
ROU and DEF 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.
For standard profile library cross-sections and pair sections the stiffeners are handled as follows:
For the following form codes edge stiffeners are automatically set as RUO
FC 114 Cold formed C-section
FC 115 Cold formed Omega section
FC 116 Cold formed C-Section eaves beam
FC 118 Cold formed ZED section
FC 119 Cold formed ZED section asymmetric lips
FC 120 Cold formed ZED section inclined lip
FC 121 Cold formed Sigma section
FC 124 Cold formed Sigma section eaves beam
FC 126 Cold formed ZED section both lips inclined
FC 129 Cold formed Sigma section asymmetric
FC 130 Cold formed 2C-section
For the following form codes edge stiffeners are automatically set as DEF
FC 117 Cold formed C-Plus section
FC 122 Cold formed Sigma section stiffened
FC 123 Cold formed Sigma-Plus section
FC 125 Cold formed Sigma-Plus section eaves beam
FC 127 Cold formed I-Plus section
FC 128 Cold formed IS-Plus section
For the following form codes internal stiffeners are automatically set as RI
FC 121 Cold formed Sigma section
FC 124 Cold formed Sigma section eaves beam
FC 122 Cold formed Sigma section stiffened
FC 123 Cold formed Sigma-Plus section
FC 125 Cold formed Sigma-Plus section eaves beam
FC 128 Cold formed IS-Plus section
FC 129 Cold formed Sigma section asymmetric
Within this paragraph special cases for the Initial Shape generation are listed.
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.
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 ensures consistency between EN 1993-1-1 and EN 1993-1-5. For further information reference is made to Ref.[40].
As specified in EN 1993-1-3 art. 1.1(3) CHS & RHS members are checked according to EN 1993-1-1.