1. Module 5
Beam Modeling

2. 5. Beam Modeling
Beam elements are line elements used to create a one- dimensional idealization of a 3-D structure.
They are computationally more efficient than solids and shells and are heavily used in several industries:
Building construction
Bridges and roadways
People movers (trams,
railcars, buses)
Etc.
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3. ...Beam Modeling
In this chapter, we will present a brief introduction to beam modeling via the following topics:
A. Beam Properties
B. Beam Meshing
C. Loading, Solution, Results
D. Workshop
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4. Beam Modeling A. Beam Properties
The first step in beam modeling, as with any analysis, is to create the geometry — usually just a framework of keypoints and lines.
Then define the following beam properties:
Element type
Cross section
Material
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5. Beam Modeling ...Beam Properties
Element Type
Choose one of the following types:
BEAM188 — 3-D, linear (2-node)
BEAM189 — 3-D, quadratic (3-node)
ANSYS has many other beam elements, but BEAM188 & 189 are generally recommended.
Applicable to most beam structures
Support linear as well as nonlinear analyses, including plasticity, large deformation, and nonlinear collapse
Ability to include multiple materials to simulate layered materials, composites, reinforced sections, etc.
Ability to create “user defined” section geometry
Easy to use, both in preprocessing and postprocessing phases
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6. Beam Modeling ...Beam Properties
Cross Section
To completely define a BEAM188 or 189 element, you also need to specify its cross section properties.
The BeamTool provides a convenient way to do this.
Preprocessor > Sections > Common Sectns...
Select the desired shape, then enter its dimensions.
Press the Preview button to view the shape, then OK to accept it.
If there are multiple cross sections, specify a different section ID number (and an optional name) for each.
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7. Beam Modeling ...Beam Properties
A sample preview (SECPLOT) of an I-beam cross section is shown below.
In addition to the predefined cross-section shapes, ANSYS allows you to create your own, “user-defined” shape by building a 2-D solid model.
You can save user-defined sections as well as standard sections with the desired dimensions in a section library for later use.
See Chapter 15 of the ANSYS Structural Analysis Guide for more information.
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8. Beam Modeling ...Beam Properties
Material Properties
Both linear and nonlinear material properties are allowed.
After all beam properties are defined, the next step is to mesh the geometry with beam elements.
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9. Beam Modeling B. Beam Meshing
Meshing the geometry (lines) with beam elements involves three main steps:
Assign line attributes
Specify line divisions
Generate the mesh
The MeshTool provides a convenient way to perform all three steps.
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10. Beam Modeling ...Beam Meshing
Step 1: Line Attributes
Line attributes for beam meshing consist of:
Material number
Section ID
Orientation keypoint
Determines how the cross section is oriented with respect to the beam axis.
Must be specified for all cross-section types.
A single keypoint can be assigned to multiple lines (i.e, no need to specify a separate keypoint for each line).
Each end of a line can have its own orientation keypoint, allowing the cross section to be “twisted” about the beam axis.
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11. Beam Modeling ...Beam Meshing
Examples of using orientation keypoints:
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12. Beam Modeling ...Beam Meshing
To assign line attributes, use the “Element Attributes” section of the MeshTool (or select desired lines and use the LATT command).
Pick lines
Additional attributes for BEAM188 & 189
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13. Beam Modeling ...Beam Meshing
Step 2: Line Divisions
For BEAM188 and 189 elements, a single element spanning the entire beam length is not recommended.
Use the “Size Controls” section of the MeshTool (or the LESIZE command) to specify the desired number of line divisions.
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14. Beam Modeling ...Beam Meshing
Step 3: Generate the Mesh
First save the database (Toolbar > SAVE_DB or SAVE command).
Then press the Mesh button in the MeshTool (or issue LMESH,ALL) to generate the mesh.
Pick lines
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15. Beam Modeling ...Beam Meshing
To see the cross-section shape in the element display, activate the element shape key:
Utility Menu > PlotCtrls > Style > Size and Shape…
Or /ESHAPE,1
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16. Beam Modeling ...Beam Meshing
After beam meshing is completed, the next step is to apply loads and solve.
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17. Beam Modeling C. Loading, Solution, Results
Typical loading for beam models consists of:
Displacement constraints
applied at keypoints or nodes
Forces
Pressures
load per unit length
applied on element faces
Solution > Apply > Pressures > On Beams
Or SFBEAM command
Gravity or rotational velocity
acts on entire structure
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18. Beam Modeling ...Loading, Solution, Results
To obtain the solution:
First save the database.
Then solve. (Or write the loads to a load step file and solve all load steps later.)
Results review is the same as for other stress analyses:
View the deformed shape
Check reaction forces
Plot stresses and strains
The main advantage of BEAM188 and 189 is that with the element shape key activated (/ESHAPE,1), stresses can be directly viewed on the elements (similar to solids and shells).
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19. Beam Modeling ...Loading, Solution, Results
Demo:
Resume frame.db (contains lines, kp’s, loading, element type, material, and two cross sections)
Plot the two cross section already defined (SECPLOT,1 & 2)
Define a third cross section using the BeamTool:
ID=3: Name = peak, Sub-type = box (hollow rectangle), W1=6, W2=6; T1=T2=T3=T4=0.25
Bring up MeshTool, GPLOT, then assign the following line attributes:
Sloping lines: mat=1, secnum=3, orientation KP = topmost KP (#100)
Left vertical lines: mat=1, secnum=2, orientation KP = #102
Right vertical lines: mat=1, secnum=2, orientation KP = #101
Left & front horizontal lines: mat=1, secnum=1, orientation KP = #1
Right & back horizontal lines: mat=1, secnum=1, orientation KP = #3
Specify size=20 on all lines
Save, then LMESH,ALL; then EPLOT with /ESHAPE,1
Constrain the 4 bottom keypoints in all DOFs and apply a force of -10,000 lb in the fy direction on keypoint #9
Solve, then review results: deformed shape (animate), reaction forces, SX stresses (= axial + bending). Select elements with section ID=3 and replot stresses. Repeat for ID=2.
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20. Beam Modeling D. Workshop
This workshop consists of the following problem:
W4. Building Frame
Please refer to your Workshop Supplement for instructions.
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