[TowerTalk] ChatGPT

[JVarney]

Here's an example where I asked ChatGPT to calculate the
bending moment strength of Rohn 45 leg tubing.  It's quite
straightforward, a simple equation, and ChatGPT fumbles
it pretty badly here:

K6OK: For a round steel tube with outside diameter 1.50 in, inside
diameter 1.26 in, and a nominal yield strength of 50000 psi, what
is the LRFD flexural moment design strength?

ChatGPT: To calculate the LRFD flexural moment design strength
of the round steel tube, we can use the following formula:

Mn = Fy * Zx

where:
Mn = nominal flexural strength
Fy = yield strength
Zx = plastic section modulus

First, we need to calculate the plastic section modulus of the
tube. The plastic section modulus can be calculated as:

Zx = π/2 * (D^3 - d^3) / D

where:
D = outside diameter
d = inside diameter

Substituting the values given in the problem, we get:

Zx = π/2 * (1.5^3 - 1.26^3) / 1.5
Zx = 0.0552 in^3

Next, we can substitute the plastic section modulus and the yield
strength into the formula for the nominal flexural strength:

Mn = Fy * Zx
Mn = 50,000 psi * 0.0552 in^3
Mn = 2,760 in-lbs

Therefore, the LRFD flexural moment design strength of the round
steel tube is 2,760 in-lbs.

=====

K6OK:  I believe the correct equation is Z = (D^3- d^3)/6.

ChatGPT: You are correct, I apologize for the mistake in my
previous response. The correct formula for the plastic section
modulus of a hollow tube is:

Zx = (π/32) * (D^4 - d^4)

where D is the outside diameter and d is the inside diameter.

[snip for brevity]

Therefore, the LRFD flexural moment design strength of the
round steel tube is approximately 1,505.5 in-lbs.

=====

K6OK: No, your equation for Zx is for elastic section modulus.
Please use the plastic equation Zx = (D^3- d^3)/6.

ChatGPT: You are correct again. I apologize for the confusion
caused by my previous response. The correct equation for the
plastic section modulus of a hollow tube is:

Zx = (D^3 - d^3) / 6

where D is the outside diameter and d is the inside diameter.

Substituting the values given in the problem, we get:

Zx = (1.5^3 - 1.26^3) / 6
Zx = 0.0246 in^3

Then, we can use the formula for the nominal flexural strength:

Mn = Fy * Zx
Mn = 50,000 psi * 0.0246 in^3
Mn = 1,229.2 in-lbs

Therefore, the LRFD flexural moment design strength of the
round steel tube is approximately 1,229.2 in-lbs, using the
correct plastic section modulus formula.

=====

K6OK: Please check your math.  For Zx I get 0.2291 in^3.

I apologize for the confusion. You are correct, the correct
value of Zx for the round steel tube is:

Zx = (1/6) * (D^3 - d^3)
Zx = (1/6) * (1.5^3 - 1.26^3)
Zx = 0.2291 in^3

Then, we can use the formula for the nominal flexural strength:

Mn = Fy * Zx
Mn = 50,000 psi * 0.2291 in^3
Mn = 11,454.2 in-lbs

Therefore, the LRFD flexural moment design strength of the round
steel tube is approximately 11,454.2 in-lbs.

I apologize for any confusion caused by my earlier responses
and thank you for bringing this to my attention.

K6OK: That is correct now. Thank you.

=====

I'm sort of on the fence with this... while ChatGPT got this
quite wrong and I had to correct it more than once, I do think
down the road with smarter and more refined AI models we could
see some very useful tools be made available to us.

73 Jim K6OK