# Looks like AI still has a way to go

SlideRuleEra

I gave Microsoft’s AI (Bing.com) a try with the following question:

“What 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?”

Got this response:

“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?”

Looks like AI still has a way to go.

SRE

“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`

Where:

• 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`

Where:

• 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`

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`

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.”

So it completely ignored your braced length and any LTB checks? Is 50ksi an allowable stress?

But it explained and gave equations. It must be right.

@Ussuri Glad you took time to run this through Google Bard. Looks like this AI engine needs much improvement for detailed technical problems, also. Results it produced are “authoritative sounding garbage”. A few examples, but first for comparison, I got W14x34 as the minimum weight A992 beam performing hand calcs per AISC 9th Edition. Modern methods should give similar results.

1. 50 ksi is A992 yield strength. AISC 9th Edition allowable bending stress is 66% of yield strength = 33 ksi, and as you noted, braced length or LTB cannot be ignored.
2. “The minimum weight A992 steel beam needed… is a W21x44. This beam has a section modulus of 87.5 in^3…"
Wrong: Section Modulus of a W21x44 is 81.6 in^3, not 87.5 in^3.
3. “The W21x44 beam weighs 35.4 pounds per foot, which is less than the maximum allowable weight of 40 pounds per foot.”
Wrong: W21x44 weighs 44 pounds per foot, not 35.4 pounds per foot.
Wrong: There is no “maximum allowable weight” requirement in the problem, and if there was 44 pounds per foot is certainly NOT less than 40 pounds per foot.
4. “In this case, the bending moment is: M = 1200 lb/ft * 27 ft^2 / 8 = 40500 lb-ft”
Wrong: This AI cannot even do arithmetic, M = 109,350 lb-ft
5. “The maximum allowable weight for a steel beam is typically 40 pounds per foot.”
Ridiculous, I’ll stop there.

Since at least yesterday, this type AI problem is not longer hypothetical at ET. There is a member now posting “answers” to questions where his “answers” were generated by ChatGPT… with all its’ flaws. He has started doing this without revealing the AI input. Expect this will hasten the demise of ET as less experienced members there will accept this inaccurate “nonsense”. This member tried the ChatGPT input on a question I’m responding to. I called his hand, nothing more said so far by anyone… will see what happens.

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Interesting discussion! Unfortunately some of the numbnuts out there will take those answers as gospel and run with them…dangerous…particularly when companies are less inclined to have competent, senior engineers reviewing and mentoring the unwashed.

The danger comes from the successful user that gets things done faster than the rest by sneaking in AI answers here and there. They develop the habit, but then promoted higher, where they understand less and must AI more to keep up. Eventually the exceed their Peter Principle skill, and mistakes are made.

If this happens to some bloggers and social media influencers, no big loss. If this happens to some doctors or engineers, the loss could be very great indeed.