The Critical Weakness of the I-Beam

This video explains the major weakness of the "I-shape". The main topics covered in this video deal with local and global buckling as well as torsional problems around I-beams. We compare different shapes of beams and analyze their behavior under eccentric loads. The inability of the I-beam to carry torsional loads is illustrated through a numerical example.

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References:

[2] A. F. Hughes, D. C. Iles and A. S. Malik, Design of Steel Beams in Torsion, Ascot: The Steel Construction Institute, 2011.
[3] B. J. G. James M Gere, Mechanics of Materials, Stamford, Conn., 2009.
[4] A.F.F. Dynamics Laboratory, Beam Torsion: Stress Analysis Manual, 1986.

[Chasmodee]

As a mechanical "structural" engineer for over 35 years, I must disagree with the idea that an I-Beam has a fatal flaw. When designing anything, there are typical, predefined structural members that, if properly used, will result in nothing but a successful design. The error here is a misapplication of a known element of design. For instance, one can not say the nail has a fatal flaw because it does not hold steel together or welding is flawed because it does not attach wood to steel.

[NvTwist]

There’s a massive difference between A flaw in the design & a design limitation. If a engineer choose to use square tubing in place of an I- beam its not the tubing thats flawed… its a fatal flaw with-in the engineer not the tubing.

[geoffconroy]

The illustration is not a 'I' beam but classed as a universal beam, 'I' beams have radii in the corners universal beams do not hence they do not have the same resistance to torsional loads.. They are cheaper and therefore easier to manufacture.

[milantrcka]

Quite instructive. Destructive is the "music". Please drop it!

[ByWire-ykeh]

Very well explained, and it demonstrates the kinds of choices structural engineers make. I saw this in an engineering statics course I took in 1969. Hasn't changed much expect that now computers can model these structures much, much, much better than we could with slide rules (slip sticks).

[felimz]

Structural Engineering Ph.D. here. Good content and animations, but the video fails to acknowledge why the I-beam is the most efficient shape in steel structures. In fact, its popularity likely is an indicator or how non-fatal the torsional I-beam weakness is and, as you have noted, there are plenty of ways to mitigate this weakness from a design perspective. Good job, keep the videos coming.

[alexanderSydneyOz]

Yes, that is quite instructive, though it seems unwarranted to call it a "fatal flaw". Rather, as I take the video, all configurations have their weaknesses, and torsion is simply the I Beams weakness. So it is used where it won't see those forces.

[andyharpist]

An engineer will choose a beam shape or construction design that gives equal resistance to all of the these failure modes. A thicker flange will help prevent tortion failure

[howardosborne]

This could have been really informative and educational if it weren't for the silly music competing with the narration. Is there really any benefit from overlaying music on a scientific/educational video?

[geoffreyworley]

Brilliant clear description of the weakness of the I Beam. Clear
and concise
and co

[TheEngineeringHub]

We apologies for the audio quality and loud background music. We are a growing channel and we learn from our mistakes, we will correct this in our future videos.

Also, many of you mentioned that the nomenclature of the beams might be different than the one used in your region. The name varies from place to place. In Canada, where our professional practice is, we colloquially refer to all shapes (W, H, S) derived from an "I" as I-beams. We understand that it is most likely different in your country/region.

[BillLaBrie]

Their obvious fatal flaw is that they can easily be melted by jet fuel.

[mtnman]

Answer me this: why do creators take a perfectly good video and completely ruin it with continuous background music?

[charliepearce]

I've been in the building industry for years in my younger life.
Now older retired guy, i built a hydraulic log splitter with a large "I" beam as part of the machine .
After using this machine for 15 years im surprised every now and then how this i beam wants to "Twist" under heavy load...
Ive never seen this happening in normal applications...
I ❤ my log splitter ...

[Rimrock]

I-beams are great in general, one just need the knowhow during design regarding staying well under the limits to avoid issues. Great video

[HiTechDiver]

Very interesting. The vast amount of knowledge in any given subject matter is staggering. Even if one knew everything to date, technology changes so fast there are new things to learn every day, let alone current knowledge.

[russell_szabados]

I’m not an engineer, I’m a musician. But this video satisfied an intellectual curiosity about structural engineering, so I’m looking forward to checking out more explanations about what makes large structures sound and long standing.

[drumcdoo]

Interesting... When Buncfield Depot, an oil storage facility in Hemel Hemstead UK blew up on 13th December 2005, many comercial buildings under construction within a few hundred yards ended up destroyed. Massive RSJ's (I beams) were left with twisted and buckled from the shear force of the explosion making it look like a war zone. So yes, can understand the limitations of these beams having witnessed the results first hand...

[darrinjones]

I learned these by practice. I been a carpenter 40 years. You learn what works. Just throw around a smaller, lighter beam on the job site and you can see these flaws.
Great instructions 👍

[DataLog]

Twin Towers are a prime example.
Those towers were so poorly built that I would blame the engineers for 80% of those deaths.