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MENG 421 Assignment 6

Ansys Trusses


A 3D truss from Beer, click to enlarge

Warren truss, click to enlarge









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Lecture notes -- Truss3d2a, Trussw, K Truss, Tension-only, Bridges  

For today's assignment you will first find the displacements and stresses in a three-dimensional truss. Then , you will analyze a two-dimensional truss. You will also capture and print the graphics. Some bridge photos are here.

Displacement and stresses in a three-dimensional truss
In this section you will create a three-dimensional truss and apply a load. Then you will run Ansys to determine the deflections and stresses. You will also capture the 3D graphic of the truss.

You have already learned how to use the Ansys element type Link1 for two-dimensional applications. However, you must use Link8 for the three-dimensional truss in this part. Of course, for either element type, only axial forces are allowed. That is, you must not apply transverse forces or moments to these elements.

Pan-Zoom tool
  1. Make a copy of the file truss3d2.a. This is Problem 6.40, Page 293 of Statics by Beer and Johnston, which uses Figure P6.39.
  2. For this problem there are nine elements and five nodes. We number the nodes in order -- A = 1, B = 2, etc. There are six constraints -- three at the pinned joint B (node 2), one at C (node 3), and two at D (node 4). The units are shown in metric but we will use engineering units instead. Use feet for meters and a cross-sectional area of 1 in 2.
  3. W apply the forces P = 0 and Q = (-9 kip) k, i.e., 9 kip in the -Z direction. (A kip is a kilopound.)
  4. Run this file with Ansys to see both the original and the deformed shape.
  5. Make a copy of your truss3d2.a.
  6. Edit the file putting your name and date on the /TITLE line.
  7. Change the name of the file in the /TITLE line to match the new name.
  8. Notice the Ansys command
    /COLOR,PBAK,off    ! black background
    which changes the background to a uniform black.
  9. Change the Ansys code of your copy truss3d3.a by adding another force to node 1 as in Beer Problem 6.40.
    Add force P at node 1 to be -12kip j so the total force at node 1 is -12kip j -9kip k.
  10. Notice that the FINISH command for the /POST1 section is commented out. This allows manipulation of the figure with the Zoom tool.
  11. Run the program with Ansys to get the graphic.
  12. Change the display as you did above to remove the deformed shape.
  13. Manipulate the figure with the Zoom tool.
  14. Your figure should look like this, except that black and white are interchanged.
  15. Capture the image with LView as you did in Assignment 3.
  16. Save the graphic as a GIF 89a file named Truss3d3.gif.
  17. Make the changes you did to previously (crop, effects negative, and properties gray scale).
  18. Save your graphic.
  19. Print your graphic.
  20. Notice the four types of data at the bottom of your Ansys program truss3d3.a.
  21. Delete the original data.
  22. Copy the data from Mass.txt, Displ.txt, and Stress.txt and paste it into the bottom of your Ansys program.
  23. Print the program with its data.
  24. In the Ansys Input window, second line, under Pick a menu item, type the missing finish command and press Enter.

Displacement and stresses in a two-dimensional truss
In this section you will find the weight, displacement, and stresses in a two-dimensional truss that is the prototype for your design project. You will also capture the graphics and print them.

  1. Copy the file trussw.a from the class directory.
  2. Edit trussw.a and put your name and date on the /TITLE line.
  3. Notice that the FINISH command for the /POST1 section is commented out.
  4. Clear Ansys by clicking the File menu and picking Clear & Start New
  5. Run trussw.a with Ansys (File, Read Input from).
  6. The results are in three files. The first part of the output is in the file Mass.txt, a new Output line. The displacements, forces, and stresses are in their usual files. Here are the lines that create these three files:
         /OUTPUT,Mass,txt,U:\win\Ansys\     ! mass
         /OUTPUT,Displ,txt,U:\win\Ansys\    ! displacements
         /OUTPUT,Stress,txt,U:\win\Ansys\   ! forces and stresses
  7. Check that the results agree with the data at the end of trussw.a.
  8. Copy the results into the bottom of the Ansys file.
  9. Print the combination Ansys code and results.
  10. Notice that the graphic shows both the deformed and the undeformed shape. The screen should show a uniform black background.
  11. Look at the deformed shape to see that the left end is in the original position but the right end has moved to the right. This is, of course, because the left end is pinned while the right is supported by a roller.
  12. Check that your name is on the graphic.
  13. Move the figure over your title if necessary.
  14. This is a two-dimensional truss so don't change the orientation.
  15. Capture the graphics window showing both the original and the deformed shape.
  16. Save the file with a name suggestive of the truss name. Use Trussw.gif here.
  17. Now make a second, graphic for your printed truss plan that you will start next week.
  18. Open the truss plan in a second browser so you can refer to it in the following steps.
  19. Change the display as you did above (Plot, Elements) to remove the deformed shape.
  20. Make the Ansys Graphics window smaller by dragging the lower-right corner diagonally towards the upper-left corner. Move more than half way so the truss is about four inches long. Click here to see and example.
  21. Make sure that the truss plan shows underneath.
  22. Adjust the Ansys Graphics window so the truss is the same length as those in the truss plan.
  23. Capture the figure and save it with the name Trusswtp.gif (tp means truss plan).
  24. Go back to Ansys and drag the Ansys Graphics window back to its original size.
  25. Animate the figure with the following steps.
  26. You can see a 600KB animation of the deformation:
  27. Find the first graphic file in explorer and double-click it to start the photo editor. This is the graphic with both the original and the deformed shape.
  28. Make the usual changes (reverse, gray scale, transparent) and print it.
  29. Do the same with the second file; check that it is about four inches long. You will insert this figure into your truss plan next week.
  30. In the Ansys Input window, second line, under Pick a menu item, type the missing finish command and press Enter.

  31. Assignment
    Using a word processor, make a cover sheet describing what you did. Attach the results for both parts as one report. Include the Ansys printouts and the graphics with your name and date.

  32. Before logging out check the size of your stored files.

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Revised: March 10, 2004 -- Copyright 1997-2004 ARMiller