Whats stronger DOM .250 wall or.120 wall?

[Alan2smiley]

I'm building a cross member wondering what would be better to use 1" .120 wall DOM or 1" .250 wall DOM. I'm using a 6" die.

 

[Alan2smiley]

@Buttertruck what do you think of this craziness?

 

[Alan2smiley]

I used 1" .120 because 3/4" soild fits nicely inside therefore easier and maybe stronger when fixing my mistakes.

 

[Truckman4life]

Just FYI.

Tube Size vs Strength | Rorty

Opting for thicker wall tube in the hopes of gaining greater strength is rarely a worthwhile pursuit. Usually, the major rise seen is in the weight of the

rorty.net

 

[kennyw]

I did catch someone saying that the closer the material is to the center, the less effect it has on the strength. Which makes sense.

That depends on how the material is loaded but is basically true for bending of a simply supported beam element. You can look at beam loading diagrams and see that max bending stress in a simply supported beam goes from max positive (tension) at the outer limit on one side to zero on the neutral axis (center of a tube) to max negative (compression) on the outer limit. The reason for structural shapes such as tubing being more popular than solid rod is the weight efficiency of having no material in the center where stress is low or zero.

 

[Alan2smiley]

All great information.

 

[anwat]

I only understand about half of what you guys are talking about, but this looks like a great place to ask something that has been bothering me for a while. I can remember back in the dark ages, sitting in some college classroom and hearing the professor talking about how the triangle was the strongest shape. I don't know if he meant strongest supporting weight, or tensile, or what, but I've always wondered why you never see triangle shaped tubing or stock at metal yards, you see rectangular, square, round, but never three sided. We're always triangulating stuff to make it stronger, so it sounds like there may be some truth to the statement.
Sorry if it's a stupid question, but it sounds like one of you could probably answer that one pretty easy.

 

[Alan2smiley]

I only understand about half of what you guys are talking about, but this looks like a great place to ask something that has been bothering me for a while. I can remember back in the dark ages, sitting in some college classroom and hearing the professor talking about how the triangle was the strongest shape. I don't know if he meant strongest supporting weight, or tensile, or what, but I've always wondered why you never see triangle shaped tubing or stock at metal yards, you see rectangular, square, round, but never three sided. We're always triangulating stuff to make it stronger, so it sounds like there may be some truth to the statement.
Sorry if it's a stupid question, but it sounds like one of you could probably answer that one pretty easy.

I don't understand all of it either but it's interesting.

 

[bp71k5]

I only understand about half of what you guys are talking about, but this looks like a great place to ask something that has been bothering me for a while. I can remember back in the dark ages, sitting in some college classroom and hearing the professor talking about how the triangle was the strongest shape. I don't know if he meant strongest supporting weight, or tensile, or what, but I've always wondered why you never see triangle shaped tubing or stock at metal yards, you see rectangular, square, round, but never three sided. We're always triangulating stuff to make it stronger, so it sounds like there may be some truth to the statement.
Sorry if it's a stupid question, but it sounds like one of you could probably answer that one pretty easy.

If the professor said that he was incorrect. It CAN be a very strong structure in some situations, but certainly not all. Archways in ancient buildings being but one example of where a triangle wouldn’t be so useful. It depends on the materials, weight, and all kinds of other factors.

Gravity is always pushing things downward. To prevent a “thing” from moving downward you can put something under it as the best way to prevent its moving downward. But sometimes you don’t want something directly under it, but you can tolerate something on each side. In that case you could add two stiff beams that both support the load at the “top” and spread out the beams at the “bottom” forming a triangular structure that’s open directly below the thing that wants to move downward but still strong enough. There’s lots of other cases where different structures work better given a bunch of other constraints.

 

[Alan2smiley]

Triangle structure would be comparable to roof rafters.

 

[anwat]

If the professor said that he was incorrect. It CAN be a very strong structure in some situations, but certainly not all. Archways in ancient buildings being but one example of where a triangle wouldn’t be so useful. It depends on the materials, weight, and all kinds of other factors.

Gravity is always pushing things downward. To prevent a “thing” from moving downward you can put something under it as the best way to prevent its moving downward. But sometimes you don’t want something directly under it, but you can tolerate something on each side. In that case you could add two stiff beams that both support the load at the “top” and spread out the beams at the “bottom” forming a triangular structure that’s open directly below the thing that wants to move downward but still strong enough. There’s lots of other cases where different structures work better given a bunch of other constraints.

Makes sense. Decks on bridges are often braced in a triangle fashion, but the spans themselves are usually arches of some sort. Interesting, but it's certainly too late in life for me to pursue engineering.

 

[Buttertruck]

Hey, you know those thick walled cardboard tubes you get inside rolls of shrink wrap- they sure seem stronger than paper towel rolls. About the same outside diameter too.

 

[scouthead]

i would say the way the tubing is attached to the mounting points, and the way the welding is done is more important to consider than .120 vs .25 for a crossmember like this.

the frame on the truck is going to flex. it just is...
I would worry about the frame cracking around a crossmember that will not move, and i would worry about welds failing at the connection points

so how rigid do you want the new super duper crossmember? -stiffer than superman the time Lois jumped in the booth to make a call while he was changing???

 

[anwat]

Hey, you know those thick walled cardboard tubes you get inside rolls of shrink wrap- they sure seem stronger than paper towel rolls. About the same outside diameter too.

and they won't rust!