Bending Information for Shell Profiles
- Last UpdatedDec 04, 2025
- 4 minute read
The bending information is calculated as follows:
Consider the longitudinal bar outlined as in the images below.
The following assumptions are made:
When the bar is bent, there exists a neutral curve on the bar along which neither stretching nor contraction of the material occurs.
The neutral curve is a parallel curve to the trace at a distance d from it:
The Bent Longitudinal
d is the distance from the point F to the line L (see the Bent Longitudinal image: F is the foot point of the cross-section of the bar. C is the center of mass of the cross-section. L is the line through C perpendicular to the web plane of the bar.)
F is the foot point of the cross-section of the bar
C is the center of mass of the cross-section.
L is the line through C perpendicular to the web plane of the bar.
The material in the bar will be stretched in the length direction of the bar on one side of the neutral curve and contracted on the opposite side. The stretching or the contraction in the direction perpendicular to the curve can be neglected. Suppose first that the bar has been bent (see the Bent Longitudinal image). A straight line - the bending line - is fitted to the neutral curve.
Suppose then that the bar will be rectified (see the Longitudinal before the Bending image). Then the bending line will be transformed to a curve - the inverse bending curve whose coordinates (in uv-system of the unbent bar) are tabulated in the bending table. In the current bending process, the bar will be bent until the inverse bending curve has changed to a straight line.
The Longitudinal before the Bending
If the curvature of the bar is large, the bending line may intersect the flange or the trace or it may somewhere lie closer to them than ip BEND_DIST (see below). In such cases, the line will be translated until it lies between the limits. If this is impossible, the bending line will be divided into two or more overlapping lines according to (see the Two Overlapping Bending Lines image)
Two Overlapping Bending Lines
The following keywords in the restriction file for profiles are affecting the calculation of the inverse bending curves for shell profiles (see The Restriction File):
|
Keyword |
Affecting |
|---|---|
|
BEND_DIST |
The minimum distance between the bending line and the flange or trace. Default value is 50. See also figure below |
|
DIST_BEND_POINTS |
Defines the distance between the reference points in the bending table(s) for the bending sight line(s). |
Control Information
The distance d from the neutral curve to the trace may be controlled by the following ip’s in a separate ip-file called na_ctrl.ip.
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[NA_CTRL, NGROUPS, <ngroups>, |
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|
PROFILE_TYPE, <prof_type>, NPROFPARAM, <nprp>, (PROFPARAM, <prp>, (1...nprp) |
|
|
INSIDE, <INS>, OUTSIDE, <outs>), (1...ngroups) ] |
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|
By default, the position of the neutral axis (along which neither stretching nor contraction of the material occurs) is calculated via the center of mass of the cross-section of the bar. This position of the neutral curve can now be controlled by the user via this ip. |
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<ngroups> |
Number of combinations profile type and dimensions. |
|
<prof_type> |
The profile type of the bar. |
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<nprp> |
Number of profile parameters. |
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<prp> |
Profile parameters. |
|
<ins> |
The distance from the trace of the profile in the bending curve in case of inside bending, that means, the root of the profile will be stretched and the upper part of the profile will be contracted. |
|
<outs> |
The same as <ins> but for outside bending, that means, the upper part of the profile will be stretched and the root of the profile will be contracted. In case of inflection, that means, both inside and outside bending will occur, the inside value will be used. |