Creating a rectangular tube in CalculiX
Rectangular tubes are one of the standard shapes of beams. This article shows how to create them in CalculiX GraphiX.
Sharp corners
A rectangle with sharp corners is easiest to generate in CalculiX. In practice, these are often made by extrusion.
It is generated by the following code for cgx
:
## Define the view. rot y rot l 30 rot u 15 ## Dimensions # Rectangle parameters, width, height, wall thickness valu W / 50 1000 valu H / 50 1000 valu t / 2 1000 # Profile length valu L / 200 1000 # Divisions valu divW 20 valu divH 20 valu divt 4 valu divl 48 # Derived values valu W2 / W 2 valu H2 / H 2 valu WI - W t ## Geometry # First corner line seto l1 pnt p1 0 W 0 pnt p2 0 WI t line ! p1 p2 divt setc # Center point pnt pm 0 W2 H2 # Rectangle surface seto Face1 swep l1 l2 mir pm y divW swep l2 l3 mir pm z divH swep l3 l4 mir pm y divW swep l4 new mir pm z divH setc comp Face1 do merg p Face1 merg l Face1 ## Show the geometry valu showgeom 1 if showgeom > 0 capt Rectangular profile face geometry. plot pa all plus la all plus sa all stop hcpy png rectangular-profile-geometry sys mogrify -trim rectangular-profile-geometry.png endif seto profile swep Face1 Face2 tra L 0 0 divl setc comp profile do elty all he20r mesh all ## Create the mesh valu showmesh 1 if showmesh > 0 frame capt Rectangular profile mesh. view elem plot e all n view surf stop hcpy png rectangular-profile-mesh sys mogrify -trim rectangular-profile-mesh.png endif
The geometry and resulting mesh look as follows.


Rounded corners
Steel profiles often have rounded corners because of the way they are manufactured. The following code generates such a profile. The basic concept is to create a line and sweep that to form 1/4 of the profile. This is then mirrored two times and merged. By default, the internal radius equals the wall thickness. This is generally considered the minimum value:
## Define the view rot y rot r 135 rot u 25 ## Parameters # Width, height and length in [m] valu B 0.10 valu H 0.15 valu L 0.25 # Wall thickness [m] valu t 0.004 # Number of elements in Y valu dy2 6 # Number of elements in Z valu dz2 8 # Twice the number of elements in the radius valu dr 8 # Twice the number of elements in X valu dl 24 # Calculated values valu B2 / B 2 valu H2 / H 2 valu B2i - B2 t valu H2i - H2 t valu Ri t valu cpy - B2i Ri valu cpz H2i valu ncpy - 0 cpy ## Geometry seto tube-section pnt ! 0 B2i 0 swep tube-section new tra 0 t 0 4 swep tube-section ln2 tra 0 0 cpz dz2 pnt cpt 0 cpy cpz swep ln2 ln3 rot cpt x 90 dr swep ln3 new tra 0 ncpy 0 dy2 copy tube-section new mir z copy tube-section new mir y setc merg p tube-section merg l tube-section ## Show the geometry valu showgeom 0 if showgeom > 0 capt Rounded rectangular profile face geometry. plot pa all plus la all plus sa all stop hcpy png rounded-rectangular-profile-geometry sys mogrify -trim roundedrectangular-profile-geometry.png endif ## Extrude the tube seto tube swep tube-section new tra L 0 0 dl setc comp tube do ## Mesh the tube elty all he20r mesh all ## Show the mesh valu showmesh 0 if showmesh > 0 frame capt Rectangular profile mesh. view elem plot e all n view surf stop hcpy png rounded-rectangular-profile-mesh sys mogrify -trim rounded-rectangular-profile-mesh.png endif
The profile and mesh look as follows.


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