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Beam Modeling

Module 5. Beam Modeling. 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

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Beam Modeling

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  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. October 30, 2001 Inventory #001571 5-2

  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 October 30, 2001 Inventory #001571 5-3

  4. Beam ModelingA. 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 October 30, 2001 Inventory #001571 5-4

  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 October 30, 2001 Inventory #001571 5-5

  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. October 30, 2001 Inventory #001571 5-6

  7. 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 ANSYSStructural Analysis Guide for more information. Beam Modeling...Beam Properties October 30, 2001 Inventory #001571 5-7

  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. October 30, 2001 Inventory #001571 5-8

  9. Beam ModelingB. 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. October 30, 2001 Inventory #001571 5-9

  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. October 30, 2001 Inventory #001571 5-10

  11. Beam Modeling...Beam Meshing • Examples of using orientation keypoints: October 30, 2001 Inventory #001571 5-11

  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 October 30, 2001 Inventory #001571 5-12

  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. October 30, 2001 Inventory #001571 5-13

  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 October 30, 2001 Inventory #001571 5-14

  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 October 30, 2001 Inventory #001571 5-15

  16. Beam Modeling...Beam Meshing • After beam meshing is completed, the next step is to apply loads and solve. October 30, 2001 Inventory #001571 5-16

  17. Beam ModelingC. Loading, Solution, Results • Typical loading for beam models consists of: • Displacement constraints • applied at keypoints or nodes • Forces • applied at keypoints or nodes • 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 October 30, 2001 Inventory #001571 5-17

  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). October 30, 2001 Inventory #001571 5-18

  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. October 30, 2001 Inventory #001571 5-19

  20. Beam ModelingD. Workshop • This workshop consists of the following problem: W4. Building Frame Please refer to your Workshop Supplement for instructions. October 30, 2001 Inventory #001571 5-20

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