The following is a step-by-step procedure for analysis a two-dimensional truss structure using SAP2000.  The order of some of these steps is not critical; however, all step should be completed before execution of the the analysis. If you have any questions, or you you find any of these instructions unclear or inaccurate, please contact Dr. Charles Camp.

To help students become familiar with some of the numerous aspects and features of SAP2000, the following tutorial will focus on determining the forces in each member of the roof truss shown below. Assume all members are pin connected.

When you start SAP2000 Educational Version 7.4 you should see the following interface window:

Step 2: Grid Spacing - Determine the appropriate number of grid line and grid spacing to locate the joints of the truss. The grid spacing is set by defining a new problem.  To create a new problem, select New Model under the File menu.

Step 3: Locate Truss Joints - To define the joint locations, select the Draw Special Joint button on the lower tool bar. Click on grid intersection lines to define joints. For this problem the joint locations are shown below:

Step 4: Draw Frame Elements - To define each frame element, select the Draw Frame Element button on the lower tool bar. To define an element, click on a joint at the beginning of the element and than on the joint at the end of the element. To end a series of element definitions, simply double-click on the final joint. For this truss problem, the frame elements are shown below:

Step 5: Define Structural Supports - To define the location and type of structural support, select the support location by clicking on the joint with the pointer. A yellow "X" should appear at the joint to indicate that it is currently selected. Next click on the Joint Restraint button on the bottom tool bar.

After the supports have been defined the truss problem should appear in the SAP2000 interface window as follows:

Step 6: Apply Forces at Joints - To apply forces at a joint, select the joint with the pointer and click on the Assign Joint Loadings button .  The following menu will appear:

Step 7: Release Internal Moments at Joints - SAP2000 assumes that all structures are frames. Therefore, to analyze a truss structure we should convert each joint from a fixed connection to a pin connection. To ensure that every joint in the structure is pin connected, select all the members by clicking the Select All button on the bottom tool bar. Next click on Assign menu and select Frame then Releases and the and Frame Releases window will appear.

Step 8: Define Material Properties - SAP2000 assumes the loads acting on a structure include the weight of each weight. In our truss analysis, we assume that each element is weightless. To define the properties of a material , select the Define menu located along the top the SAP2000 interface window and then click on Materials. The Define Materials window will appear as shown below:

Change the value in the Weight per unit Volume input field to zero. Click OK to return to the Define Materials window and than click OK again. Now we have a material named OTHER that has no weight per volume. For this example problem, the default values for the Mass per unit Volume, Modulus of elasticity, Poisson's ratio, and the Coeff of thermal expansion can be used. For most linear elastic statically loaded structures only values for Weight per unit Volume and Modulus of elasticity are required.

 Step 9: Define Frame Sections - To define the cross-section properties of a structural element click on the Define menu located along the top the SAP2000 interface window and then click on Frame Sections. The Define Frame Sections window will appear as shown below:

The default Frame Section label is FSEC1. To change the properties of the frame section click on the  on the Modify/Show Material button. The Rectangular Section window will appear.

To the material of this frame section click on the Material pull-down menu and select our weightless material OTHER. Click OK to return to the Define Frame Sections window and than click OK again. If you are interested in computing deflections in the truss, then you must define the Depth (t3) and Width (t2) of the cross-section. In this example, we are interested only in the axial forces in a determinate truss, so the value of the cross-sectional areas are not important.

Step 10: Assign Frame Sections - To assign the cross-section properties of a structural element, select the element with the pointer and click on the Assign menu located along the top the SAP2000 interface window and then click on Frame Sections. You can assign the same section properties multiple elements by selecting all the elements that share the same properties. The Frame Section name will appear next to each element selected. After the frame sections have been assigned the SAP2000 interface window will appear as follows:

Step 11: Set Analysis Options  and Run Analysis - In this example, the truss structure is modeled in the x-z plane. To limit analysis to variables in the x-z plane click on the Analyze menu located along the top the SAP2000 interface window and then click on Set Options. The Analysis Options menu will appear as follows:

To restrict SAP2000 to variables in the x- plane, select the Plane Frame button and click OK. The truss structure is now ready for analysis. To analyze the model press the Run Analysis button .

If the analysis is successful, the Analysis Complete window will appear and report the the analysis is complete.  Click OK and the SAP2000 interface window will display an exaggerated deflected shape of the modeled structure.

If the window reports that the analysis is incomplete, make sure that the moments have been released and that the analysis options have been set correctly.

After the Analysis Complete window has been closed, typically SAP2000 displays the deflected shape of the structure as shown below:

Step 12: Print Truss Forces - To get a quick feel for the relative magnitude of the forces in the truss, select the Member Force Diagram for Frames button along the bottom tool bar. The Member Force Diagram for Frame menu will appear as follows:

The default values will display the Axial Forces using the Fill Diagram. If you click OK, the SAP2000 interface window will display the relative magnitude of the axial forces with compress forces in red and tension forces in yellow.     Another way to display force information is to unclick Fill Diagram and click on Show Values on Diagram. In this case, the value of each axial force will be displayed next to the member (see the figure below).

To print the results to a file click on the File menu and select Print Output Tables and click the Print to File box. There is an option for Spreadsheet Format if desired. The default location for the file is the same directory as the problem files. A different location can be specified by clicking File Name and choosing the desired file location and name.

In order to correlation the results printed in the output file to frame elements in the structure, the frame labels turned on and printed out. To display the frame element labels click on the Show Undeformed Shape button on the main interface. Next, click on the Set Elements button and under the Frame section of the menu click on Labels.

The frame element numbers, or any other information displayed in the main SAP2000 interface, can be printed by clicking on the File menu and selecting Print Graphics (the image will be sent to the default printer).

The results of the truss analysis presented in the output file are listed by frame element number.

Note that SAP2000 list the variation of the internal forces and moments along the element. For truss analysis there are no bending moments and shear forces. The values listed in the "P" column are the axial forces in the truss members.

This website was originally developed by Charles Camp for CIVL 3121. This site is maintained by the Department of Civil Engineering at the University of Memphis. Your comments and questions are welcomed.