New Super Duty Frame: Engineers, do you see any "tricks" here?

[naaman]

Here is a video where they hang 8 4700-lb pick up trucks from the frame of the new Super Duty F250. Then they hang an additional 13,000-lb truck from the frame. Do you see any "cheating" going on with regard to the rigging or in any other way? Skip to 9:30.

<iframe width="560" height="315" src="https://www.youtube.com/embed/8EvOEyBVpok" frameborder="0" allowfullscreen></iframe>

 

[texmorales]

Well as a structural engineer I can't stand ads like this which misrepresent and skew the test to get the desired outcome.

Notice how the red brackets from which they hang all these trucks from is not located at the true attachment points for the suspension and axels which are spaced farther away from the lift points...instead they are positioned as close to the lifting point as possible...meaning less of a moment arm and hence less force. If they were a few inches closer they would be almost perfectly inline with the lift point! So to clarify, if they located the lift points say on the rear at the actually points the rear leaf springs attach to the frame the moment arm would be much greater and represent real world use and this thing would certainly fail in spectacular fashion. I would actually love to watch that ad!

Unfortunately, the general public will miss this and instead be wowed. As a professional engineer we have a code of ethics barring this kind purposeful misrepresentation...however since this is their marketing team and no actual real world use is technically being applied here... I guess no harm no foul. And I am sure somewhere in the fine print of this ad it says all that about this being a staged act...blah blah blah.

That being said having a fully boxed frame is definitely the way to go for added strength and rigidity, although you take a hit on weight and thus fuel economy.

 

[hkz286]

Plus it's a static load test so whilst impressive it's not really representative of the cyclic loading that's subjected to a vehicle chassis in use. So no fatigue, impact, heat stress etc is present

Still kinda cool though!

 

[Zoom]

Yeah it's more a demonstration of the crane capacity and those attachment cables than anything else. Nice setup though. Shows how much you can lift with these relatively thin cables...

 

[naaman]

Well as a structural engineer I can't stand ads like this which misrepresent and skew the test to get the desired outcome.

Notice how the red brackets from which they hang all these trucks from is not located at the true attachment points for the suspension and axels which are spaced farther away from the lift points...instead they are positioned as close to the lifting point as possible...meaning less of a moment arm and hence less force. If they were a few inches closer they would be almost perfectly inline with the lift point! So to clarify, if they located the lift points say on the rear at the actually points the rear leaf springs attach to the frame the moment arm would be much greater and represent real world use and this thing would certainly fail in spectacular fashion. I would actually love to watch that ad!

Unfortunately, the general public will miss this and instead be wowed. As a professional engineer we have a code of ethics barring this kind purposeful misrepresentation...however since this is their marketing team and no actual real world use is technically being applied here... I guess no harm no foul. And I am sure somewhere in the fine print of this ad it says all that about this being a staged act...blah blah blah.

That being said having a fully boxed frame is definitely the way to go for added strength and rigidity, although you take a hit on weight and thus fuel economy.

I thought something like that might be going on, but lack the technical understanding to identify it.

I was just curious, really, and I appreciate everyone's input.

 

[Aaron94T]

Well as a structural engineer I can't stand ads like this which misrepresent and skew the test to get the desired outcome.

Notice how the red brackets from which they hang all these trucks from is not located at the true attachment points for the suspension and axels which are spaced farther away from the lift points...instead they are positioned as close to the lifting point as possible...meaning less of a moment arm and hence less force. If they were a few inches closer they would be almost perfectly inline with the lift point! So to clarify, if they located the lift points say on the rear at the actually points the rear leaf springs attach to the frame the moment arm would be much greater and represent real world use and this thing would certainly fail in spectacular fashion. I would actually love to watch that ad!

I hear what you are saying and the ad would have been more impressive if they mounted the brackets at the actual suspension mounting points. However, I do not think they claimed that they were mounted at the suspension points. The closer they mount to the center line of the truck the less the moment arm becomes which I am sure they were well aware of. With that said, the test shows that a box frame is seriously strong if made with the proper gauge steel! My question after watching that spectacle would be were frame failures on the previous Superduty a leading problem that needed to be fixed?

 

[Zoom]

Very likely the failures were at solder joints. If they built it in a way that a joint was at a flexion / torsion point, reminding even such a frame is somewhat elastic, repeated stresses would lead to failure. I didnt check the particular case of this "superduty" chassis though, but that's a general case that the dynamics have to be considered rather than a static load.