ETABS 2016 Tutorial: Bars and Shafts

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

only. The procedure of analysis in ETABS 2016 is similar to that of ETABS v9.

Example

Determine the external support reactions at the fixed supports A and B. Draw the internal axial

force and torque moment diagrams. The member is made of A992 Steel and has a diameter of 3

inches.

Solution

Step One: Open ETABS.

Step Two: Select “New Model”.

A

B

200 lb-ft

300 lb-ft

1.5 kips

2 ft

4 ft

3 ft

Step Three: Select the Initialization Options. For this example, we will select “Use Built-in

Settings”.

Step Four: Specify a grid spacing and story height (based on your problem). Note that the Z-

coordinate defines the gravity direction. This is specified by the “Story Dimensions”. Working

in the xz plane, we will specify 10 grid lines in the x-direction, with a spacing of 1 ft. Since we

can model this member as a single one-dimensional line segment, the number of stories is

irrelevant.

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

In the 2D window, change the view to elevation 1. This will take us to the xz elevation view.

Remember that the number of stories is irrelevant for this example since we can model out

system as a one-dimensional line.

Step Five: Define material properties.

Modify the material properties by making the mass and weight per unit volume zero. We will

assume the material weight is zero so as to not induce unwanted shears and moments. Let’s

modify the A992Fy50 Steel since our member is made of this material.

Step Six: Define frame sections.

For this example, we are given that the member is a circular rod with a 3 inch diameter. Add a

new section that is a circular steel rod. To do this, first select “General” under the “Special” set

of selections. Note that we can define as many new sections as we need for a given problem.

We will name this “1A”.

Step Seven: Now we shall draw our member.

Make sure you select the “1A”s section in the “Properties of Object” tab. Change the external

supports to fixed connections by selecting “Assign”, then “Joint”, then “Restraints”.

Step Eight: Next, we shall apply our loads. Select the member, then under the “Assign” menu,

select “Frame Loads”. Assign the point load at a relative distance of 7/9 = 0.778 from A in the

Global-X direction. Assign the torque moments at relative distances of 3/9 = 0.333 from A and

7/9 = 0.778 from A in the Global-X direction.

Step Nine: Now we run our model by selecting the “play” button. To display the axial force

and torque moment diagrams, select the button shown below.

Below are the axial force and torque moment diagrams, respectively.

If you noticed that something seems off about these diagrams, you are correct. The diagrams

should not have any linear segments. To eliminate this misleading output, “unlock” the model,

select the member, click “Assign”, “Frame”, and “Output Stations”. Change the “Min Number

Stations” to a large number. Let’s set it to 5,000. What this means is that ETABS will report

and plot internal loads at 5,000 evenly-spaced locations along the member. Also, we can change

the “End Length Offsets” to zero in order to display the diagrams over their appropriate lengths.

Re-running and displaying the numerical values gives the correct axial and torque diagrams,

respectively.