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I was looking through the facebook page of a roll cage / fab company and this picture was shown (looked like a drag car, not a real race car):

 

No automatic alt text available.

 

That makes me cringe... but I don't actually know how much 'less safe' that would be than a solid tube. Anyone know?

Issues would be: 

- That local point now has no resistance to bending inward

- Strength of that pin in double-shear compared to strength of a tube

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6 minutes ago, Ron_e said:

Used in swing-out door bars to make it more convenient for the street.

Maybe for handicap race cars as well.  Hero's Motorsport uses something like that I think.

Not nearly as dangerous as the guy who was racing at an SCCA event when I was working as a flagger earlier this year.  He had to live on Oxygen and somehow he was allowed to have it in the car with him.  Because "It isn't in the rules that you can't have an oxygen tank in the car with you".  Isn't @dogtired the one who has "Where's the Kaboom? There was supposed to be a big Kaboom" in his signature line?

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1 hour ago, Jamie said:

Plus it’s double shear! @enginerd I expected a calculation or something from someone with a username like that. Paging @Hi_Im_Will and @Huggy for the math. 

Calculating the double shear isn’t difficult, it’s the other parts that are tough:

1) how much load would fail the same section if it was a solid tube

2) how much weaker (in resisting being bent inward) is that tube as a whole now that it has a 1 dof joint in the middle. Even if it doesn’t shear the pin, that ‘bar’ is going to deform more compared to a single tube. 

Edited by enginerd
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8 hours ago, enginerd said:

Calculating the double shear isn’t difficult, it’s the other parts that are tough:

1) how much load would fail the same section if it was a solid tube

2) how much weaker (in resisting being bent inward) is that tube as a whole now that it has a 1 dof joint in the middle. Even if it doesn’t shear the pin, that ‘bar’ is going to deform more compared to a single tube. 

2. The joint isn't in the middle, it's close to one end. That changes the resistance to bending.

 

It's been about 25 years since my statics and dynamics courses but I seem to remember doing cantilever calculations and hinged vs solid. Worst case for hinged is in the middle, best case for hinged is at one end.

 

Not as safe as a continuous door bar but safer than no bar at all. :)

Edited by mender
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On 1/12/2018 at 4:16 PM, lenbo211 said:

Maybe for handicap race cars as well.  Hero's Motorsport uses something like that I think.

Not nearly as dangerous as the guy who was racing at an SCCA event when I was working as a flagger earlier this year.  He had to live on Oxygen and somehow he was allowed to have it in the car with him.  Because "It isn't in the rules that you can't have an oxygen tank in the car with you".  Isn't @dogtired the one who has "Where's the Kaboom? There was supposed to be a big Kaboom" in his signature line?

What event and class was this?  SCCA always preached " just because it isn't in the rule book doesn't mean you can".  Unreal !

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