simple rod problem

8/18/2019 Simple Rod Problem

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Solving a Simple Pin-jointed Truss Problem using FEMAP

You need to solve the problem illustrated below by hand and using FEMAP. Let E=200 GPa for

each bar. Suggested steps for an FEMAP solution are listed below. We will use units of

millimeters, kilograms, and milli-Newtons for length, mass, and forces, respectively.

1. Start up FEMAP. We will first create the three nodes. Select the menus Model/Node as

shown below. In the window that pops up, enter X=0, Y=0, and Z=0 and press OK.


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2. As with most input windows in FEMAP, the window does not go away. You have created

the first node and the program is waiting for coordinates of a second node. Enter X=500,Y=0, and Z=0. Next enter the coordinates X=500, Y=400, and Z=0. Press the Cancel button

to terminate creation of nodes. From the menus, select View/Autoscale/Visible (or the keys

Ctrl A). You should now see the three nodes.


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3. Select the menus Model/Material . In the Define Material window, Key in a title and 200E6

kPa for Youngs Modulus as shown below. The remaining material properties can remainzero (why?). Click OK and then Cancel.


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4. Select the menus Model/Property. In the window that pops up, key in a title, select the

material we just created, and then click the button as shown below.


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5. In the Element/Property Type window, click the Rod radio button and click OK. Rod

elements in NASTRAN are truss type elements with pinned joints. The can not transmit bending moments.


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6. Back in the Define Property window, we will enter the physical properties. They are cross

sectional area and torsion constant. The torsion constant is the polar moment of inertia for anassumed circular cross section. Key in the values as shown below and click OK. In the next

window change the title and the area and torsion constant values as shown below. Note the

ID values in the upper left hand corner are 1 and 2. Click OK and Cancel.


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8. Select from the menus Model/Element . In the window that pops up, make sure the Property

is set to “1..Rod Area 200 mm^2” and then click in the first node box on the left as shown below. Now select the two bottom nodes as shown below and click OK. Next, change to

Property 2, click in the first node box, and click the two vertical nodes as shown below.

Click OK and Cancel.

Pick this

node first

Pick this node

second

Pick this

node first

Pick this node

second


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9. We can turn on a representation of the cross section of these rod elements. FEMAP assumes

the cross section is round. From the icons on the ribbon bar, select the Thickness/CrossSection option as shown below. Your mesh should look like the one below. The horizontal

element is a bigger diameter than the vertical element, as expected. Toggle the cross section

display off by selecting this icon again.

10. Now we will create the nodal restraints (supports). From the menu’s, select

Model/Constraint/Nodal . Because a constraint set has yet to be created, a window opens to


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give the new constraint set a name. In the first window that pops up, key in a title for the

restraint set and click OK.


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12. We need to restrain the lower left hand node in the Z direction (why?). Next click this node

as shown below and then click the checkbox for the TZ and click OK and Cancel. Yourscreen should now look like the view below.

Pick this node


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13. We will now apply the 10,000 N load. From the menus select Model/Load/Nodal . In the

window that pops up, key in a title for the load set and click OK.


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14. A new window pops up to select nodes. Pick the node shown below and click OK. In the

Create Loads on Nodes window, make sure force is selected and key in the force componetsas shown below (note units are mN). Click OK and then Cancel.

Pick this node


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15. We are now ready to solve the model. From the menus select Model/Analysis. In the

window that pops up, click the New button.


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16. In the Analysis Set window that pops up, key in a title for the analysis. The Analysis

Program and Analysis Type pull-down menu items should be as shown below. Click OK.Back in the Analysis Set Manager window, now click the Analyze button.


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17. A window titled NX Nastran Analysis Monitor shows up on the left side and allows you to

monitor the progress of the solution. Give the program a few seconds to solve and whencomplete, the status message changes to “Complete” as shown below. Click the X button to

close this window.


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18. You can quickly display the deformed grid by clicking the icon.


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19. Lets look at the axial forces in each member. Press the key F5. In the View Select window

that pops up, click the Deform radio button under “Deformed Style” and the Criteria radio button under “Contour Style” as shown below. Next click the “ Deformed and Coutour

Data” button. In the Select PostProcessing Data window, set the parameters as shown in the

second window below and click OK twice to close both input widows.

20. Your screen display should look like the following. Clearly these are the correct results.


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21. Now examine element stresses. Click the icon from the ribbon bar (or press the F5 keyagain and click the “Deformed and Coutour Data” button). In the Select PostProcessing Data window. Set the Contour parameter as shown below and click OK to close the input

widows.


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22. Select from the menus File/Print to print out a black and white (or grayscale) copy of the

screen hand in for this homework assignment. In all your FEMAP problems, you do notneed to make color copies to hand in.

23. To examine the computed displacements of node 2, select from the menus List/Output/Query.

In the window that pops up, select from the Category pull-down menu select Displacement ,click the Node radio button and lastly click in the ID input box. Now select node 2 (the one

that moves). Note that node number 2 is put into the ID box as shown below. Click OK.The Messages box at the bottom of your FEMAP window lists displacement data for node 2as shown below.

24. On the page you previously printed, perform a hand calculation to verify the computedstresses and displacements. Hand in the results.

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