Artificial Intelligence vs. Specific Engineering Problems

Much news about AI engines such as ChatGPT, Google Bard, Bing AI, and more.

On another engineering website, AI generated “answers” to technical questions are being posted as facts… without revealing that the content of these “answers” is produced by AI. The results appear to be what you might expect, well written, authoritative sounding content that is often incomplete, inaccurate or technical nonsense, but may be convincing to engineers not familiar with the specific type problem

Recently, a technical question was “run through” a couple of AI engines with mixed results (In one case, the AI engine said it could not answer the question. A different site provided grossly inaccurate gibberish).

Here is the question used, will be interesting to see results others get from the various programs available:

“What is the minimum weight A992 steel beam needed for a 27 feet simply supported span, with 9 feet maximum unbraced length and uniform distributed load of 1200 pounds per foot?”

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According to Google Bard. The answer is:

“The minimum weight A992 steel beam needed for a 27 feet span, with 9 feet maximum unbraced length and uniform distributed load of 1200 pounds per foot is a W21x44. This beam has a section modulus of 87.5 in^3, which is greater than the required section modulus of 72.5 in^3. The W21x44 beam weighs 35.4 pounds per foot, which is less than the maximum allowable weight of 40 pounds per foot.

To calculate the required section modulus, we can use the following formula:

Code snippetS = M/F

Use code with caution. Learn more


  • S = section modulus (in^3)
  • M = bending moment (lb-ft)
  • F = allowable stress (psi)

The bending moment is calculated using the following formula:

Code snippetM = wL^2/8

Use code with caution. Learn more


  • w = uniform distributed load (lb/ft)
  • L = span length (ft)

In this case, the bending moment is:

Code snippetM = 1200 lb/ft * 27 ft^2 / 8 = 40500 lb-ft

Use code with caution. Learn more

The allowable stress for A992 steel is 50,000 psi. Therefore, the required section modulus is:

Code snippetS = 40500 lb-ft / 50,000 psi = 81 in^3

Use code with caution. Learn more

The W21x44 beam has a section modulus of 87.5 in^3, which is greater than the required section modulus of 81 in^3. Therefore, this beam is sufficient to support the load.

The maximum allowable weight for a steel beam is typically 40 pounds per foot. The W21x44 beam weighs 35.4 pounds per foot, which is less than the maximum allowable weight. Therefore, this beam is also within the weight limit.”

Which all sounds very comprehensive as long as you don’t check the output.

Response for Microsoft’s Bing AI:

“I’m sorry, but I couldn’t find any specific information about the minimum weight of an A992 steel beam for a 27 feet span, with 9 feet maximum unbraced length and uniform distributed load of 1200 pounds per foot. Would you like me to search for something else?”

Isn’t this a problem that you look up in a table? If the AI has digested that table, then the answer is immediate, and correct every time.

Hero points to @Ussuri for putting up with Bard as long as it took to generate and post that answer, but I would expect the right answer to come WITHOUT calculations, if the AI had been fed the proper tables already.

Not how your college teacher demanded to show your work, but AI turns everything upside down, of course.

Where did that come from?

No idea but it would suggest you are not allowed to use most of the W-shapes.

“Isn’t this a problem that you look up in a table?”

Bingo! I succeeded in “boiling down” a common structural engineering problem to minimal “number crunching”.

And to answer the above question… Absolutely Yes, the way I solved the problem is that simple… Look It Up In a “Table”… so let’s do that right here:

Step 1: Do some grade-school math:
Moment = 0.125 x 27 x 27 x 1.2 = ??? Answer: 109.4 Kip-Feet

Step 2: Pull out the appropriate book. I chose American Institute of Steel Construction (AISC) Manual of Steel Construction, 9th Edition, Allowable Stress Design… there are other books, methods, software, etc.

Step 3: Turn to the relevant page… Page 2-207, in this case. Scan of this page shown below.

Step 4: On Page 2-207 go to intersection of 109.4 Kip-Feet and 9 Feet Unbraced Length

Step 5: Simply read off the answer… W14x34.

All Information Needed For A Solution Has Been On The Internet For Years.

Since The Problem Is That Simple , Why Can’t AI Solve It?



So, Bard doesn’t know that ^ means exponent.

And gained a zero somewhere along the way.

Could you explain “unbraced length” to this non-structural engineer please. Maybe Bard will read the answer and learn also.

@MintJulep Explain “unbraced length”. Sure, and that’s a good question.

First, there is a more modern term, “lateral torsional buckling” (LTB), but it’s basically the same thing as “unbraced length”.

The geometry of an “I” type beam (gravity bending loads carried almost exclusively by the top [compression] and bottom [tension] flanges) causes a “long” beam to distort and twist as vertical load is applied. This will cause the beam to fail long before it’s theoretical load carrying capacity is reached. Here is an image of how a “long” beam will distort under just gravity loads:


If the compression (top) flange is horoizontally externally braced (or with web stiffeners, but that for another time), LTB can be controlled. In the example, I stated that unbraced length was 9 feet. For this beam that two braces on the 27 ft. long beam, like this (braces in red)

LTB-2 Braces

And the answer is a W14x34 (i.e. a “W” series beam that is 14 inches tall and weighs 34 pounds per foot.)

If one brace was used at the center of the 27 ft. beam, unbraced length is 13.5 feet, and the answer becomes a W12x40.

LTB-1 Braces

No braces, just a 27 ft. beam, and the answer is W12x58.

There is more to selecting a beam than this question addresses, like deflection, but that is separate from unbraced length.

Thanks, that’s what I imagined.

I found this interesting/amusing.


Now that was eye opening!

This article really describes the AI created technical posts I’ve read… broad, grand generalities and little meaningful content. The referenced 1987 paper’s hypothetical analogy of how an 1890’s AF (artificial flight) machine may have been designed by “engineers” who had only limited insight into real requirements for flight is interesting.

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There is no ‘e’ in ketchup. I thought it was tomatoes?

How many toes in tomatos?

Tomatoes do not have toes. Tomatoes are fruits that are botanically classified as berries. They are members of the nightshade family, Solanaceae, which also includes potatoes, eggplants, and peppers. Tomatoes are a good source of vitamins A and C, and they are also a good source of lycopene, an antioxidant that has been linked to a reduced risk of cancer.

Toes are the digits on the feet of humans and other animals. They are used for walking, running, and grasping objects. Tomatoes do not have feet or toes, so they cannot walk, run, or grasp objects.

Do you believe it’s time for companies to incorporate usage of AI Tools into their employee and security procedure manuals? Many employees must comply with conditions such as responsible use of social media, confidentiality, secure transactions. Many IT departments impose restrictions on company network access to sites like Facebook and Youtube. Would that be appropriate for AI tools?

If your knee-jerk reaction is “make it stop”, then consider this:

I have many colleagues who use Grammarly, which turns out to have an AI learning algorithm behind it.

Recent updates to MS Word and Outlook have incorporated predictive text algorithms - not exactly AI but Microsoft is up-talking their claims and promising more and better in the future.

A guy in my company’s marketing department claims that he’s already run chatGPT for some text which he’s posted to Linkedin.