Calculating Polybeams
Not version-specific
Tekla Structures
Environment
Not environment-specific
Modeling
When modeling curved or segmented parts in Tekla Structures, it is important that the parts modeled are calculated to the correct fabrication length. We recommend using the Polybeams functions instead of segmented beams, for example. Using other methods than polybeams function can lead to incorretly calculated rolled/curved lengths.When taking the profile shape into account, you should be careful. For example, depending on the preference of the detailer or the shop, a rolled wide flange shape may be calculated along the top flange, but a swept beam may be calculated along the beam centerline.
Angles may be calculated along the heel or vertical leg, but the shape of the angle provides several ways the piece could be rolled, and having the proper settings can adjust whether the piece be calculated along the inside edge or the outside edge.
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Polybeams are created by picking multiple points to define segmented lengths of a part. Those points or handles can be modified with different chamfer options, and the size of these chamfers can be adjusted.
For more information, see Modeling > Detaling Structures > Fine-Tuning Part Shape > Chamfers > Corner chamfer types and dimensions in the Tekla Structures Help.
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There are some advanced options that affect how Tekla Structures calculates these parts, and also a file called unfold_corner_ratios.inp.
Advanced Options
While there are many advanced options that affect polybeams, not just their length but how they unfold and appear on drawings, this guide will be focusing on three of them.XS_USE_OLD_POLYBEAM_LENGTH_CALCULATION
• If this variable has any value, then it is activated and the unfold_corner_ratios.inp file is ignored. This variable is not recommended, since it calculates by adding the straight lengths together and does not consider unfolding (the stretch or shrink of the length along the curve). Default is blank.
XS_CALCULATE_POLYBEAM_LENGTH_ALONG_REFERENCE_LINE
• If this variable has any value, it is activated. Any polybeams will be calculated along the reference line, regardless of the rotation or position values. If the old polybeam length calculation variable is also activated, then this variable has no effect. This variable also does not affect parts with Arc chamfers. The values in the unfold_corner_ratios.inp file will override this setting. Default is blank.
XS_UNFOLDING_DONT_USE_NEUTRAL_AXIS_FOR_RADIUS
• If this variable has any value, it is activated. Any polybeams with radius chamfers will be calculated along the inside curve of the profile. Blank will read from centerline. Any setting for this variable is overwritten by the unfold_corner_ratios.inp values. Default is TRUE.
Unfold Corner Ratios file
The unfold_corner_ratios.inp file is read from the system folders, but can also be placed in a Firm, Project, or Model folder. The file works by defining profile types and how they should be calculated based on chamfer type and position values.Here is a sample line from the unfold_corner_ratios.inp file:
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Type
• 1 is for polybeams
• 2 is for plates modelled as polybeams (profile e.g. PLT)
• 3 is for parts which are not unfolded and follow the old polybeam calculation (for example the line 3 L* * disables unfolding of L profiles)
• 2 is for plates modelled as polybeams (profile e.g. PLT)
• 3 is for parts which are not unfolded and follow the old polybeam calculation (for example the line 3 L* * disables unfolding of L profiles)
Profile
• You can set the profile type/size, or use an asterisk to include all profile types and sizes.
Material
• Material grade can be defined, or an asterisk can be used to include all material grades.
Rotation
• For polybeams: the minimum and maximum angle when the profile is rotated around its longitudinal axis. 0 to 360 will not work, for a full range it works from -180 to 180.
• For plates: the minimum and maximum thickness of the plate in mm.
• For plates: the minimum and maximum thickness of the plate in mm.
Flag
• 1 is for sharp folds
• 2 is for curved bends
• 2 is for curved bends
Angle/radius
• Sharp folds: the minimum and maximum angle of sharp folds
• Curved bends: the minimum and maximum radius of curved bends
• Curved bends: the minimum and maximum radius of curved bends
Ratio
• Determines which edge the length is calculated on: 0 = inside, 1= outside, 0.5 = centerline, etc.
Using these settings we can adjust how Tekla calculates polybeams of all types of profiles in many different positions.
As an example, to measure along the heel of an angle regardless of the rotation settings we need different options for the different rotations. To cover the four quadrants of rotation possible our settings can look like below:
1 L* * -180 -91 2 0 200000 1
1 L* * -90 -1 2 0 200000 1
1 L* * 0 89 2 0 200000 0
1 L* * 90 180 2 0 200000 0
This could be further simplified to two rows, the rotation from -180 through -1 can be set to 1 (outside edge) and 0 through 180 degrees can be set to 0 (inside edge).
Plates can also be defined, for example with the values below:
2 PL* * 0 19.1 1 -180 180 0
2 PL* * 19.2 102 1 -180 180 .5
The number 2 indicates these are plates - this tells the file to treat the first numbers as thickness values, not rotation values. The first line sets plates between 0 and 19.1mm (3/4”) of any bend angle to be calculated along the inside of the bend. The second line sets any plates between 19.2mm and 102mm to be calculated along centerline.
Using combinations of these settings, we can calculate any profile type or shape in any number of ways to meet different shop or detailing practices as needed. The unfold_corner_ratios.inp file will read from a Firm or Project folder, or even from the main model directory.