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Determine the nodal deflections, reaction forces, and stress for the truss system shown below (E = 200GPa, A = 3250mm²).

(Modified from Chandrupatla & Belegunda, Introduction to Finite Elements in Engineering, p.123)

Preprocessing: Defining the Problem

1. Give the Simplified Version a Title (such as 'Bridge Truss Tutorial').

   In the Utility menu bar select File > Change Title:

   

   The following window will appear:

   

   Enter the title and click 'OK'. This title will appear in the bottom left corner of the 'Graphics' Window once you begin. Note: to get the title to appear immediately, select Utility Menu > Plot > Replot

2. Enter Keypoints

   The overall geometry is defined in ANSYS using keypoints which specify various principal coordinates to define the body. For this example, these keypoints are the ends of each truss.

   • We are going to define 7 keypoints for the simplified structure as given in the following table

     keypoint	coordinate
     	x	y
     1	0	0
     2	1800	3118
     3	3600	0
     4	5400	3118
     5	7200	0
     6	9000	3118
     7	10800	0

     (these keypoints are depicted by numbers in the above figure)
   • From the 'ANSYS Main Menu' select:
     Preprocessor > Modeling > Create > Keypoints > In Active CS

     

     The following window will then appear:

     

   • To define the first keypoint which has the coordinates x = 0 and y = 0:
     Enter keypoint number 1 in the appropriate box, and enter the x,y coordinates: 0, 0 in their appropriate boxes (as shown above).
     Click 'Apply' to accept what you have typed.
   • Enter the remaining keypoints using the same method.

     Note: When entering the final data point, click on 'OK' to indicate that you are finished entering keypoints. If you first press 'Apply' and then 'OK' for the final keypoint, you will have defined it twice!
     If you did press 'Apply' for the final point, simply press 'Cancel' to close this dialog box.

   Units
   Note the units of measure (ie mm) were not specified. It is the responsibility of the user to ensure that a consistent set of units are used for the problem; thus making any conversions where necessary.

   Correcting Mistakes
   When defining keypoints, lines, areas, volumes, elements, constraints and loads you are bound to make mistakes. Fortunately these are easily corrected so that you don't need to begin from scratch every time an error is made! Every 'Create' menu for generating these various entities also has a corresponding 'Delete' menu for fixing things up.

3. Form Lines
   • In the main menu select: Preprocessor > Modeling > Create > Lines > Lines > In Active Coord. The following window will then appear:

     

   • Use the mouse to pick keypoint #1 (i.e. click on it). It will now be marked by a small yellow box.
   • Now move the mouse toward keypoint #2. A line will now show on the screen joining these two points. Left click and a permanent line will appear.
   • Connect the remaining keypoints using the same method.
   • When you're done, click on 'OK' in the 'Lines in Active Coord' window, minimize the 'Lines' menu and the 'Create' menu. Your ANSYS Graphics window should look similar to the following figure.

     

The keypoints must now be connected

We will use the mouse to select the keypoints to form the lines.

Disappearing Lines
Please note that any lines you have created may 'disappear' throughout your analysis. However, they have most likely NOT been deleted. If this occurs at any time from the Utility Menu select: