Thread: Roll Cage Design 101

Originally Posted by [b

Quote[/b] (Garrett @ Sep. 13 2005,9:21)]What exactly is a dead tube? Basically we are working with a structure known as a "frame," so I dont think you could mean zero-force member. Hook me up wih info! thank you.

a tube that doesnt add any integrity or protection to an area, just kinda pointless, and/or can be removed without and consequences.

Under what loading conditions - Bending, torsion, shear? Because it is a frame structure (mainly of all cantilever beams due to welding) one of these conditions will be true. Im still kinda confused.

Originally Posted by [b

Quote[/b] (Garrett @ Sep. 14 2005,11:25)]Under what loading conditions - Bending, torsion, shear? Because it is a frame structure (mainly of all cantilever beams due to welding) one of these conditions will be true. Im still kinda confused.

You are overthinking the dead tube idea. Its a tube that doesnt really add integrity or help to the structure (tubes meeting at certain intersections) . So shear,torsion, and bending i guess.

Does anyone have pictures of how they tied into the frame,on an extra cab ranger?

so a dead tube would be like a designer piece of tubing for looks essentially. Coolness thanks beater.

The phrase "dead tube" is also used to describe a "T" joint, where one tube dead ends into another tube. It is preferable to have multiple tubes meet at a single point, or node.

Originally Posted by [b

Quote[/b] (Garrett @ Sep. 14 2005,11:25)]Under what loading conditions - Bending, torsion, shear? Because it is a frame structure (mainly of all cantilever beams due to welding) one of these conditions will be true. Im still kinda confused.

please stop with the mumbo jumbo talk.

Haha, yeah were not building rockets here.

now Im confused again. If it's a "T" and it takes a point load, or even a distributed load, at the welded intersection (on the plane perpendicular to the page), how is it different than an "X" taking the same load? I know one is stronger, obviously, there is more distribution under both loading conditions and more material..

Im looking at this as the roof of the cage, so Im limiting loading to North / South, East / West, and again In / Out of the page.

hahah Im just not understanding. Thanks for your help.

I think my last post was confusing. Essentially, since all the beams in a cage setup are catilever beam structures due to welding, they resist moment. One Cage design will respond better to resist the moment (s) created by a point load or distributed load. Again Im lost ...

Originally Posted by [b

Quote[/b] (Garrett @ Sep. 17 2005,8:31)]I think my last post was confusing. Essentially, since all the beams in a cage setup are catilever beam structures due to welding, they resist moment. *One Cage design will respond better to resist the moment (s) created by a point load or distributed load. Again Im lost ...

you are over analyzing the dead end tube concept, just go buy 2 shitty ass cars, cage one up with lots of dead end tubes and one without and throw them down a mountain and see which one works out better

I just want to know how a beam or tube becomes a cantilever beam or tube by welding?

Originally Posted by [b

Quote[/b] (Garrett @ Sep. 16 2005,4:54)]now Im confused again. If it's a "T" and it takes a point load, or even a distributed load, at the welded intersection (on the plane perpendicular to the page), *how is it different than *an "X" taking the same load? I know one is stronger, obviously, there is more distribution under both loading conditions and more material..

Im looking at this as the roof of the cage, so Im limiting loading to North / South, *East / West, and again In / Out of the page.

hahah Im just not understanding. Thanks for your help.

"you talked a lot, but said nothing"

how does a "T" differ from an "X"? hmmmmm...

Originally Posted by [b

Quote[/b] (garagebuilder @ Sep. 17 2005,9:17)]

Originally Posted by [b

Quote[/b] (Garrett @ Sep. 16 2005,4:54)]now Im confused again. If it's a "T" and it takes a point load, or even a distributed load, at the welded intersection (on the plane perpendicular to the page), *how is it different than *an "X" taking the same load? I know one is stronger, obviously, there is more distribution under both loading conditions and more material..

Im looking at this as the roof of the cage, so Im limiting loading to North / South, *East / West, and again In / Out of the page.

hahah Im just not understanding. Thanks for your help.

"you talked a lot, but said nothing"

how does a "T" differ from an "X"? hmmmmm...

man pit jesus wanted to brawl after that comment i made a while back.. good times.

Dont over analyze the situation, think energy flow and continuity. If something pushes on this tube how will it distribute the load?

“how does a "T" differ from an "X"? hmmmmm...” – garagebuilder

hmmmmm looks like you completely misunderstood the whole damn thing. Obviously they look different, and the stress distribution across each member will be entirely different for a T or an X given the same type of loading. I know this already smarty_pants. This is basic structural analysis. I’m not sure if you’re aware of this, but any structure, especially something as complex as a skyscraper, is designed primarily with one fundamental law of physics, namely Newton’s 2nd law. Engineers analyze, and design things using laws of physics not B.S “concepts” such as dead tubes…. Wtf is a dead tube still, something you pulled from your ass. Hey I give birth to dead tubes everyday, and they’re called shits. Since you seem to know exactly what this Dead Tube concept is, tell me. And using some engineering, explain to me its purpose, and the purpose of knowing what they are, or how to find them. Knowing what, and how to find, a zero force member has a purpose.

Furthermore, if a perpendicular intersection (T) is the definition of a dead tube, then an X has two perpendicular intersections, hence “two dead tubes.” I’m lost.


“I just want to know how a beam or tube becomes a cantilever beam or tube by welding?” – sandman21

As far as a tube becoming a cantilever structure because of welding - The tubing is not simply pinned together it's welded.
A cantilever type support, by definition, resists moments and forces in all three cartesian axis (meaning x y and z coordinates). A pin support does basically the same, but supports moment and force reactions in only two axes. What this means for a cage is that the cantilever support will distribute the loads to all members, hence there are no zero force members. All tubes essentially see some fraction of the applied force (and we are neglecting force due to gravity). The extent of which is determined by the geometry of the design (as everyone knows T isn’t the same as an X).


“you are over analyzing the dead end tube concept, just go buy 2 shitty ass cars, cage one up with lots of dead end tubes and one without and throw them down a mountain and see which one works out better” - johnlagna

If one doesn't know what a dead tube is, it is more likely for one to use them if said concept exists. Anyways, from my above reply, more tubes means the load will be distributed among a larger number of members. This will effectively decrease the force on each member and correspondingly the stress on each member. Lower stresses are what accounts for the cage with more tubes as being “stronger.” That doesn’t help with me knowing what a dead tube is. I couldn’t build many not knowing how to even construct a design.

“please stop with the mumbo jumbo talk.” – mattrick8888

Sorry for the Entry level Strengths course “mumbo jumbo.” Engineers, use this “mumbo jumbo” to send monkeys into space. I may not be able to weld, but Engineers at JPL aren’t paid 150K a year to weld.

Instead of calling me an idiot, could someone explain this to me? What about all those who don’t know what a dead tube is? I’m sure they need help as well.

garret, your using engineer technology to talk to normal people, they will not understand what your saying.

a "dead tube" is a tube that "dead ends" into another tube instead of into an intersection of tubing.


here is an example of what "dead tubes" are (not talking shit to the owner of this truck, i realize in this pic its probably not done yet its just an example of the term, keep your pants on)

now....if you did this (green lines represent added tube placement) these would cease to be dead end tubes.

Originally Posted by [b

Quote[/b] (Garrett @ Sep. 22 2005,7:18)]“how does a "T" differ from an "X"? hmmmmm...” – garagebuilder
hmmmmm looks like you completely misunderstood the whole damn thing. *Obviously they look different, and the stress distribution across each member will be entirely different for a T or an X given the same type of loading. I know this already smarty_pants. *This is basic structural analysis. *I’m not sure if you’re aware of this, but any structure, especially something as complex as a skyscraper, is designed primarily with one fundamental law of physics, namely Newton’s 2nd law. *Engineers analyze, and design things using laws of physics not B.S “concepts” such as dead tubes…. Wtf is a dead tube still, something you pulled from your ass. *Hey I give birth to dead tubes everyday, and they’re called shits. Since you seem to know exactly what this Dead Tube concept is, tell me. And using some engineering, explain to me its purpose, and the purpose of knowing what they are, or how to find them. Knowing what, and how to find, a zero force member has a purpose.

Furthermore, if a perpendicular intersection (T) is the definition of a dead tube, then an X has two perpendicular intersections, hence “two dead tubes.” I’m lost.
“I just want to know how a beam or tube becomes a cantilever beam or tube by welding?” – sandman21
As far as a tube becoming a cantilever structure because of welding - The tubing is not simply pinned together it's welded.
A cantilever type support, by definition, resists moments and forces in all three cartesian axis (meaning x y and z coordinates). *A pin support does basically the same, but supports moment and force reactions in only two axes. *What this means for a cage is that the cantilever support will distribute the loads to all members, hence there are no zero force members. *All tubes essentially see some fraction of the applied force (and we are neglecting force due to gravity). The extent of which is determined by the geometry of the design (as everyone knows T isn’t the same as an X).

That would be a fixed-end support, not a cantilever type support. *A bed cage is a cantilever structure, a tube welded at each end is not, and there can be zero force members in there.
The dead tube concept has to do with load path, not how a tube intersects, you should be able to understand why a dead tube is not desired

Beautiful! Thanks guys. Seriously best responses to date!.Thanks for your time guys. (Sandman1 and esb4130) Thanks for clearing this up.

So to keep this going, since I do believe there is a lot information here for people ..

Sandman1 --- Awesome distinction. I see what you're saying here. Fixed support = both a moment and force. Yeah so that is the support type, and the structure is a cantilever beam structure. Awesome! These are the kind of threads that bring faith back into the internet.

Thanks again.
Garrett

well, cage design i think is one of the things that seperates a profesional job from an amature job. not that some amatures dont do a good job, but theres way more to it than just making it straight or having good welds. the cage's purpose isnt strictly "a roll cage", its the CHASIS of the vehicle thats keeping it from flying apart. yes, in most cases even a poorly designed cage is better than none, but theres alot of simple stuff out there that most people just dont know or dont think about. understanding where the primary forces are being applied to the chasis and how to use tubing to account for it, is a science and an art, and is far too often not well-thought out enough, and i think often underbuilt. our race truck got alot of shit for "being too heavy" and whatnot...but look, we rolled and it did not bend, didnt even dent a tube or crack a weld. id think that says something for its construction and proves that its purpose doesnt have to be just to save your life, it can save the car too.

Your race truck's cage was gnarly and built very well I will surely agree there. It's like I said over on DRides, its easy to say what sort of combination of tubing is strong, but being a lemming about it isn't a good thing. It's nice to understand why something is strong, then you can decide whether you need it or not, or if the job can be done with 1 piece of tubing rather than 2 (going back to your weight issue).

I think I was Dan V. that said "there's not such thing as over built in the desert," and I will agree there. Over built and safe is better than... well you get the idea haha. But being competitive is also why a lot of people are out there and if it can be done better then may the better man win!

any one have any pix of a cage in a regular cab chev

Originally Posted by [b

Quote[/b] (Garrett @ Sep. 23 2005,11:54)]Your race truck's cage was gnarly and built very well I will surely agree there. *It's like I said over on DRides, *its easy to say what sort of combination of tubing is strong, but *being a lemming about it isn't a good thing. It's nice to understand why something is strong, then you can decide whether you need it or not, or if the job can be done with 1 piece of tubing rather than 2 (going back to your weight issue).

I think I was Dan V. that said "there's not such thing as over built in the desert," and I will agree there. Over built and safe is better than... well you get the idea haha. *But being competitive is also why a lot of people are out there and if it can be done better then may the better man win!

To continue our agreement on DRides...I think that most people don't get the idea of applied forces...they see a "dead tube" and regardless of whether it is a addressing a primary force (i.e. a rear-end banging into the frame rails) they get all hot and bothered and believe they need to remove it or somehow work in some triangulation...but a "dead tube" could be a member connecting to planes that reduces torsion on 2 axis, expand load distribution, etc….as you said, “A pin support does basically the same, but supports moment and force reactions in only two axes. *What this means for a cage is that the cantilever support will distribute the loads to all members, hence there are no zero force members”….of course these “T’s” should be avoided if the member is receiving a primary forces, but that doesn’t mean that “dead” tubes” are useless and don’t add structural stability…that is a ridiculous claim (I.E. – JonMC –“You are overthinking the dead tube idea. Its a tube that doesnt really add integrity or help to the structure (tubes meeting at certain intersections) . So shear,torsion, and bending i guess.
”). *I guess what I’m saying is that if the “dead tube” member isn’t taking a primary forces, then I see no problem having it as part of the structure…in fact, I’d recommend it. *Any reduction of torsion, shear, bending is good, yes? You people are insane for thinking otherwise….and I really didn’t enjoy my strength of materials class…maybe it was just the professor…ever wonder why they call it that seeing as the really has nothing to do w/ the strength of materials? Blah, blah, blah…I don’t think we’ll ever win.

sick write up

Well we it's nice to have an informative thread every once in a while. Thank you nostradamus. As far as STrength of Materials? hmm I have no clue. Not really Strength of materials, but more intro to stress analysis of partical statics. hahah.

I like 'the statics of deformable elastic bodies'...makes me sound smarts, dang gum!

hahah I like that one. ACtually that is what it actually is. hahahah Lets see I'm doing my Beam deflection HW right now. Fun times!

if anyone could post that link to the website that has a tutorial on how to use the Jd2 that would be helpful. I think it was on explorer forums or some 4x4 website

www.pirate4x4.com i think

yeah here it is thanks

http://www.pirate4x4.com/tech/bendin_tube/index.html

im going to bump this old add becouse it is verry usefule and a lot of us should read it

Very usefull thanks..

Originally Posted by az/willis

im going to bump this old add becouse it is verry usefule and a lot of us should read it

too bad all the pics dont show up, due to the site update.

Very good write up.

Theres a lot of information here, I think they're can be a lot more directed to the "at-home" garage builders. I would like to know more about a cage structure as a whole. All the points in a cage that take a load (ie- shock and bump mounting areas). Where does all that force end up? the center of the chassis? C-Pillar?

This should be a sticky...

it's hard to say exactly what points or members take a load for any given case just because there are SO many different cases out there that will put a different force into the system.

It comes with experience and R&D to decide what cases you should design to.

For example, you just mentioned shock & bump mounts. it is possible to analyze the distribution of loads through your cage as the truck goes down the road, or over particular terrain (3' woops for example) with some data acquisition or knowledge of the shock and whatever else. But what you have to consider, is that you generally always want to design to the worst case. For us, the worst case is a 'gnarly' rollover. Now, you should also recognize that each rollover can be different and you're going to get forces coming into the cage from all sorts of different points - this makes it impossible to size your cage to that case. (It's different than designing a cage around a single load that you know the truck will get - as some might do for a bumper) So, all you can really do is design the various components of your cage to be as strong as possible within the parameters of your project and your capabilities, which is what the original writeup aims to do.

As far as where the forces go... they distribute from the point of loading through the entire truck - tubes, sheet metal, seats, driver, whatever else you have. The cage is there to take the load and distribute it through the rest of the tubing so you don't get breaks at any number of places.

Hope that helps.

Originally Posted by coopaaron0

Very good write up.

Theres a lot of information here, I think they're can be a lot more directed to the "at-home" garage builders. I would like to know more about a cage structure as a whole. All the points in a cage that take a load (ie- shock and bump mounting areas). Where does all that force end up? the center of the chassis? C-Pillar?

This should be a sticky...

The energy is dispersed among the structure. The geometry of your structure and the loading (magniuted and direction) will determine the magnitudes.

Ask yourself:

-Where will the loadings on the structure occur?
-How can i build a structure that will disperse this energy the most effectively
-Where will cyclic fatigue occur?
-How can i design my structure to keep from fatigue induced failure
-How can i do all this w/ the least amount of material?

Originally Posted by 1450ranger

The energy is dispersed among the structure. The geometry of your structure and the loading (magniuted and direction) will determine the magnitudes.

Ask yourself:

-Where will the loadings on the structure occur?
-How can i build a structure that will disperse this energy the most effectively
-Where will cyclic fatigue occur?
-How can i design my structure to keep from fatigue induced failure
-How can i do all this w/ the least amount of material?

Ok this makes sense.. This is where triangulation comes into play to disperse the loads. I couldn't imagine the thought that goes into a unlimited class chassis like a TT or 1 car...

Originally Posted by 1450ranger

-How can i do all this w/ the least amount of material?

this is a very important question that is often overlooked. Check out the DAKAR truck we built. It does all of this then uses the least amount of tubing to execuite the plan. Some may think the cage is a bit underbuilt for the weight, but when looking at the design closely you notice the engineering behind each tube placement. We spent four times as much time mapping out the tube work then actually doing all the fab.

Jason

Originally Posted by jason@gmachine

this is a very important question that is often overlooked. Check out the DAKAR truck we built. It does all of this then uses the least amount of tubing to execuite the plan. Some may think the cage is a bit underbuilt for the weight, but when looking at the design closely you notice the engineering behind each tube placement. We spent four times as much time mapping out the tube work then actually doing all the fab.

Jason

post a pic of it on here for us,,,,,,,,,,,,,,,,,, also there is a link on this post that explains how to map out the amount of tube a bend will take,, i know there are a lot of new guys that need to read this. it will help keep you from overshooting or undershooting a bend and having to sleve it.

Originally Posted by az/willis

post a pic of it on here for us,,,,,,,,,,,,,,,,,, also there is a link on this post that explains how to map out the amount of tube a bend will take,, i know there are a lot of new guys that need to read this. it will help keep you from overshooting or undershooting a bend and having to sleve it.

build,

DAKAR BUILD