Using unfold_corner_ratios.inp
Not version-specific
Tekla Structures
Environment
Not environment-specific
What is unfold_corner_ratios.inp?
Unfold_corner_ratios.inp is a file which contains information Tekla Structures uses to unfold polybeams and thus measure their length. By using a “Ratio” value between 0-1, the file indicates to Tekla Structures how the polybeam will be unfolded.
The file works by defining profile types and how they should be unfolded (that is, length measured) based certain characteristics of the polybeam, such as whether it has straight or curved chamfers, curvature radius, material type, profile, etc.
What variables affect unfolded length of polybeams?
The unfold corner ratios is used differently depending on whether you have modeled polybeams with straight or curved chamfers. Below is a flowchart which explains how unfold_corner_ratios.inp interacts with other advanced options.
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How Tekla Structures reads unfold_corner_ratios.inp
The unfold_corner_ratios.inp file is read from the system folders, but it can also be placed in a Firm, Project, or Model folder.
Tekla Structures will search for unfold_corner_ratios.inp in the same order as it does normally with other files, that is, Model, Project, Firm, System (environment) folders. Tekla Structures will use the first file it finds, and ignore any other. There is no merging of files. unfold_corner_ratios.inp is not used with curved beams (that is, not polybeams, but beams curved from the Beam Properties dialog box).
Format of unfold_corner_ratios.inp
The unfold_corner_ratios file is a text file which uses lines which represent certain types of polybeams. The format of each line is as follows:
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Type:
• 1 is recommended for polybeams with any profile.
• 2 is recommended for polybeams with plate profile (for example, “PL” profiles)
• 3 is for parts which are not be unfolded and follow the old polybeam length calculation (see the polybeam length flowchart above, XS_USE_OLD_POLYBEAM_LENGTH_CALCULATION). (For example, the line 3 L* * disables unfolding of L profiles.)
These type values are not exclusive. Tekla Structures recognizes all polybeam types (plates/non-plate profiles) regardless of whether, for example, “1” or “2” is used. The only difference is that on the subsequent values specified on the inp file, Tekla Structures will treat those numbers as being different things depending on which ‘Type’ value is used.
The following example will explain this more clearly. We have three polybeams, an I-beam of 300 mm thickness, and two plate polybeams with a PL300x20 profile.
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For example, if the line used is
2 * * 0 1000 1 0 180 1
All polybeams will be considered (regardless of the Type= 2). The value “1000” will be considered as a “Rotation” (in case Type = 1) or a “thickness” (in case Type =2). So for example, if the value “1000” is changed to “299”, only the third polybeam will conform.
Tekla Sturctures uses the solid extrema to determine the ‘thickness’ of the part. For instance, for the I-beam and the second plate, the ‘thickness’ would be both 300mm. The thickness of the third plate would only be 20 mm, since it is rotated.
Similarly, if the line would read:
1 * * -180 180 1 0 180 1
The third and fourth values (“-180” and “180”) would be ‘Rotation’, according to Type =1. It would apply to all polybeams though, regardless of their profile.
When a polybeam qualifies in more than one line of unfold_corner_ratios.inp, Tekla Structures will unfold the polybeam according to the first line the polybeam applies to, starting from the top of the file downwards. For example, if we had both lines:
2 * * 0 1000 1 0 180 1
1 * * -180 180 1 0 180 0
1 * * -180 180 1 0 180 0
In this case, if a polybeam conforms to both line variables, then it would be unfolded using the Ratio = 1, as indicated by the last value in the first line.
Please notice: Because of that rule. Lines starting with 1 * * or 2 * * should be placed at the end of the file because they will override all lines below them.
Profile
You can set the profile type/size, or use an asterisk as a wild card.
Material
Material grade can be defined, or an asterisk as a wild card for all material grades.
Rotation
For Polybeams (Type =1):
This value corresponds to the minimum and maximum angle when the profile is rotated around its longitudinal axis. See the image below:
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Tekla Structures will use a range of -180° to 180°. If you specify in the file 0° to 360°, it will not affect the full rotation range of the polybeam. Note that Tekla Structures may automatically change the field in the beam properties dialog box. For example, instead of ‘Top’ (+90° rotation), it may change it to ’Back’.
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What degrees correspond to what Rotation setting is Tekla Structures?
In terms of the angles that you should put in unfold_corner_ratios.inp, the angles -180° to 180° correspond to some of the Rotation settings in Tekla Structures, as follows:
Top: -180°
Back: -90°
Below: 0°
Front: 90°
Knowing this you could set up your unfold_corner_ratios.inp file so that no matter the orientation of a polybeam made with an angle profile (that is, “L” shape), Tekla Structures measures the length of the polybeam along the base/heel of the angle.
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
For Plates (Type 2):
The value corresponds to the minimum and maximum thickness of the plate in mm.
The thickness is taken as the horizontal length of the extrema box around the profile. This means that a plate profile which is 200x30 mm, could have several different ‘thicknesses’, depending on its orientation around its longitudinal axis. For example, if it is ‘flat’, then the thickness would be = 200 mm. If it is ‘standing’, then the thickness would be = 300 mm. See the example in Chapter 4.1 for an example of what this means.
What happens with a polybeam with varying plate thicknesses?
Currently, polybeams with varying profiles are not supported in Tekla Structures (TS18.0 Final).
Flag
• 1 is for sharp fold. Only polybeams with straight chamfers will be affected.
• 2 is for curved bends. Only polybeams with curved chamfers will be affected.
It is important to stress the fact that in real-life situations, polybeams with certain profiles, such as I-beams or CHS/RHS beams, are very unlikely to be manufactured using completely straight/sharp folds. Manufacturers use minimum bending radiuses, and in order to manufacture a straight corner, a special type of process would be required such as hot mould casting or by cutting and welding separate beam parts.
Straight/sharp corners are usually used with plate profiles by Tekla Structures users.
Angle/Radius
• Polybeam with straight chamfers (Flag =1):
The value corresponds to the minimum and maximum angle of the sharp folds.
The angle that is measured is that between the direction of a straight section of the polybeam, and the next section, as shown below. It is not the angle between two straight parts. See the image below.
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What values should I use if I want my polybeams to always be unfolded using the unfold_corner_ratios.inp ratio?
You should use 0 180.
Due to historical reasons, the angles that have been used are -180 to 180. This is no longer necessary. Tekla Structures will always calculate a positive angle, no matter if the beam is turning clockwise or anticlockwise, so only 0 to 180 is needed. Note also that Tekla Structures will not use any value larger than 180. See the image below for details.
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What happens if a polybeam has several bends?
When the polybeam turns many time, Tekla Structures checks each section turn, and unfolds it depending on whether its angle is within the values specified in the unfold_corner_ratios.inp. For example, see the beam below, which has two sections. The first section turns 26.75 degrees. The second section turns 63.43 degrees.
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Now we will show 3 situations.
Situation 1: Beam unfolds completely along inner surface (Ratio = 0).
1 HE* * -180 180 1 0 180 0
Length = 464.59 + 430.90 + 407.29 = 1302.97 mm
Situation 2: Beam unfolds completely along center line (ignores unfold_corner_ratios.inp – see the flowchart above).
1 HE* * -180 180 1 0 25 0
Length = 500 + 559.02 + 500 = 1559.02 mm
Situation 3: Beam unfolds first part along inner surface (angle is between 0-27), but second part along center line (angle >27).
1 HE* * -180 180 1 0 27 0
Note that a common mistake would be to add up the first two inner distances, and then the final center line distance (i.e. 464.59 + 430.90 + 500). But this would be a mistake. The correct procedure would be to imagine the polybeam unfolding by rotating its part through the points specified with the unfold_corner_ratio.inp. In this case, first section will be rotated around the inner surface corner, while the second part around the center line, as shown by the red circles below.
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If we do it in this way, the length can be easily measured measuring the unfolded straight beam, as shown.
Polybeam with curved chamfers (Flag = 2):
The value corresponds to the minimum and maximum radius (inclusive) of curved bends. The radius of the curved bend is the distance between the center of the circle defining the curvature and the center line of the polybeam, as shown below.
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If the center line radius of the polybeam is equal to or smaller than the value in unfold_corner_ratios.inp, then the polybeam is unfolded using accordingly; otherwise (if larger), unfold_cornber_ratios.inp is ignored.
What happens if the polybeam has many bends?
Similarly as with polybeam with straight chamfers, when the polybeam turns many times, Tekla Structures checks each section turn, and unfolds it depending on whether its angle is within the values specified in unfold_corner_ratios.inp. See the example under “Polybeam with curved chamfers (Flag = 2)”.
Ratio
This value determines how the polybeam will get unfolded, which in turn determines what its length will be. Specifically, it determines at which depth (perpendicular to the plane of bending/turning), Tekla Structures will unfold the beam. For example, Ratio = 0 means the polybeam will be unfolded along its inner surface (Height = 0). Similarly, 1= outside, 0.5 = center line, etc.