MENG 421 Assignment 6

Ansys Trusses

  MENG 421 -- Class assignments -- 1 2 3 4 5 6 8 9 10 11 12  

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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.

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.
   • Notice that the original elements are shown in white, the deformed elements are shown in blue, and the background is black instead of the usual graded blue. Remove the deformed shape leaving just the original.
     • Click the Plot menu and pick Elements
     • If necessary, click the Plot menu and pick Replot to show just the original elements.
   • Click the PlotCtrls menu and pick Pan-Zoom-Rotate to open the Pan-Zoom tool
   • Zoom out, and pick Obliq.
   • Check that your graphic looks like the left one above, except that black and white are interchanged.
5. Make a copy of your truss3d2.a.
   • In the right pane of Explorer right-drag the name truss3d2.a to a blank area.
   • Release the mouse button and pick Copy from the menu.
   • Rename the copy with right-click.
   • Change the file name to truss3d3.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.
    • In the Utility Menu click PlotCtrls and pick Pan, Zoom, Rotate to open the tool.
    • Try the Top, Front, Iso, Obliq, and Left buttons and the zoom in and out buttons.
    • End with the Iso button.
    • With the Zoom tool, move the figure over your name.
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.
    • Pick the PlotCtrls menu and move down to Animate
    • Move right at Animate to get a new menu
    • Pick Deformed Shape
    • Pick Def + undeformed and click OK
    • You can control the animation with the dialog box.
    • Close animation menu when you are done.
26. You can see a 600KB animation of the deformation:
    • ¤ Click here.
    • Microsoft Internet Explorer opens Media Player with full controls.
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.

  MENG 421 -- Ansys -- Lectures -- Class assignments -- 1 2 3 4 5 6 8 9 10 11 12  
Files: Ansys, Matlab, Bash

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