ETABS Tutorial: Trusses

Below is a tutorial that was organized for educational purposes at Christian Brothers University

only. The truss example below is given in Structural Analysis, 9th

ed. (Hibbeler, 2015).

Example 9.1

The cross-sectional area of each truss member is A = 0.5 in2 and E = 29(10

3) ksi.

Solution

Step One: Open ETABS.

Step Two: Select “New Model”.

Step Three: Specify a grid spacing and story height (based on your problem).

You may work in either the 2D or 3D window. Let us work in the 2D window for this example.

Step Four: Define material properties.

Modify the material properties by making the mass and weight per unit volume zero (since this is

a truss example, we will assume the material weight is zero so as to not induce unwanted shears

and moments).

Step Five: Define frame sections.

For this example, we are given A = 0.5 in2 for all members. Let us select a circular cross section

and use this for all of our members.

Step Six: Now we shall draw our members.

First, draw the bottom truss chord (as one continuous member). Make sure you select the

“frame” section that you defined earlier. Next, divide the bottom chord it into three equal

segments.

Notice that ETABS automatically placed external pin connections at the two new joints. We

need to change these to internal hinges.

Select the two interior points we want to change and click the “Assign” button. Change the joint

restraints to a single joint.

If you click on the check mark button, you can turn off the invisibility option and see the joints.

Draw the other truss members. Remember to use the “frame” section you defined earlier.

Note that for this example, we have a roller at the right support. Change the existing pin to a

roller by selecting “Assign”, then “Joint/Point”, then “Restraints”. Now, since this is a truss, we

must release all of the internal moments since trusses do not support internal moments. The

default for ETABS is a frame. That is, when you draw a structure in ETABS, it automatically

assumes a frame structure. In order to release the moments and analyze this as a truss, first select

all of the members. Then, under the “Assign” menu, select “Frame/Line” and “Frame Releases”.

Select Moment 22, Moment 33 and Torsion and set all selections to zero. (ETABS will only

allow one of the Torsion fixities to be set to zero.)

Step Seven: Next, we shall apply our loads. Select the joints where the loads are to be applied.

Under the “Assign” menu, select “Joint/Point Loads” and “Force”. For now, we will only

consider one load “combination” and we will consider it to be a dead load.

Step Eight: Now we run our model by selecting the “play” button. The model will then show

the deformed shape of the truss.

By right clicking on a joint, we may display the translation of that joint.

We may also show the member forces and stresses on the member.