steel strength vs size ?

[trailertrash]

I'm trying to build or rather have built a project out of 1" square tube steel that is pretty thick walled (1/8 " ?) now I'm ready to build the final model and was wondering where I can find info about using a bigger diameter size square tube to increase the welding surface without losing strength or increasing weight much if at all . I'm pretty sure the info is out there I just don't have a clue where. /forums/images/graemlins/confused.gif
Thank you

 

[hazmat]

You've come to the right place.

Do you have a picture or sketch of your creation? Lots of ways to optimize the strength to weight ratio.

TBN's resident Mechanical Engineer at your service /forums/images/graemlins/grin.gif

Got to go to bed now, describe your project in some better detail & I'm sure we'll be able to help you out.

 

[RonR]

Well, I'm not an eng (defer to hazmat), but I have welded a lot with 1" square tubing. If you are worried about weld joints at the corners, like a 90 degree joint, you can miter them at 45 degrees or even do a 90 degree joint and by welding around it , should have NEARLY the same strength as the other tubing.

If you are concerned about a butt joint welding it end to end, that might be more of a concern, but if there is the ability to add gussets to strengthen the joint, it should be fine. You could also insert some straps inside the tube and plug weld it to both sides of the joint, plus welding around the joint, to give it more strength.

The real question is what does it have to support. If it's a workbench or an implement stand, no problem. If it's a ground engaging implement, that might be risky.

It's worked well for me, your mileage may vary. Best wishes,

Ron

 

[Egon]

For larger stronger square tubing you may consider the type used for receiver hitches.

You could also go to a stell supplier and ask them.

Egon

 

[trailertrash]

I'll try to get a picture but in the meantime I'll try to explain this creation of mine. I run a lowboy trailer that we haul new trucks on, and with the new model trucks from IH there is no safe way to get in or out of them when they are in the air, they took the grab handles off and even the drip rails so we wind up being about 5 1/2 ft. in the air with no way up or down , gravity will get you down but thats painful ! There have been numerous attempts at ladders but none worked so I figured if you could'nt go down with a ladder go up and it seems like it will work , my prototype has been a sucess so far but I want to reduce the weight without losing the strength as it will need to support 350 lbs moving around on it to have any safety margin at all . The mount is simply a u shape made by welding 3 pieces of flat steel together , the t handle is a bolt that goes thru a nut welded over a hole in the top of the u bracket which is how it tightens on the lip, I hope this makes sense. The lip is part of the trailer and faces out , so what I do is slip the mount over the lip tighten the bolts and presto I've got a step, actually two of them the whole thing is around 30" tall which when added to the height of the trailer works very well and it is app.32" wide at the top . I can get the exact measurements tomorrow. When I started this project I used what I had laying around but now that I think it will work I'm ready to refine it to a finished product and let some of the other drivers try it and see what kind of input they have.

 

[rlw]

The formula for calculating bending stress is Mc/I. Where 'I' is the moment of inertia. Since 'I" is in the denominator of the equation, the larger it is, the lower the stress. Therefore, 'I' (moment of inertia) for a material's cross-section would be a good comparitor for sizing your material.
The formula for calculating 'I' is (b*h^3)/12. Since you have a square, its just b^4/12. This is for a solid square - since you are using tubing, you have to subtract out the inside.
So, you have: (b^4 - x^4)/12
where: b= outside dimension
x= inside dimension (b-2t), t=wall thickness

I've attached a sheet from a 'stock list' catalog with common square tubing sizes. It lists the wall thickness and weight per foot for several tubing sizes.

Now all you have to do is pick out some sizes, do the math, and compare 'I' values and weight/foot to pick your final material size.

Hope this helps and not confuses!

rlw

 

[RonR]

Wow, salute to rlw!

No offense meant by my smart **** comment. I'm sure you are correct, but I don't have clue what you described............. (grin).

Here's my response based on the description of the ladder project:

You'll never be able to stack enough fat guys on your step ladder at the same time (assuming it's like 24" wide and less than 10 ft tall and you have good weld joints) to cause 1" square tubing with .125 wall to fail.

I would more concerned with how it attached to the trailer so that doesn't fail or come undone and cause the ladder to crash down.

Disclaimer: I would still seek competent engineering approval for what you are doing, especially if you are having employees climb on this thing. Since most of the stuff I build will result only in MY injuries if it fails, I'm willing to risk more.

Best wishes,

Ron

 

[hazmat]

rlw answered for me! TBN has more than one resident engineer /forums/images/graemlins/grin.gif

your 1X1X1/8 has an I of .057 in^4. A 1.5 x 1.5 X 1/16 would be lighter with an I of .124. More than 2X stronger and the weight is slightly less. Also gives you 50% more weldable length.

As a point of reference, at my former job, we used 1.5X1.5 X1/16 steel tubing to fab roll cages for ambulances (vans with raised roofs). They have to statically (not moving) support 1.5X the van's weight = 11,000 #. It had about 8- 10 cross members, each about 60" long. Supported the weight with no problems.

Happy welding & send us a pic of the finished product (especially with the truck in the background).

 

[jmc]

Yeah but as your size increases, so does "c" in the numerator. So to compare two candidates in bending, compare bh^3 rather than bh^4.

As a practical matter, I would consider some 1 X 2, 2 1/2 , or 3 X 1/8 angle iron mounted tall side vertical. I'd guess its lower weight than an equivalent strength box and you can weld both sides. Also, some of the weight with a box is for strength in a direction you don't need it.

John

 

[yooperdave]

Structural steel tube (HSS) is hard to beat for many applications. It also tends to be one of the more expensive steels out there. A typical yield strength for hss tubing is 46 ksi while angle is lower grade material usually 36 ksi material.

Do a weight calculation prior to fabrication. The self weight of your project can get pretty heavy in a hurry.

I assume you will be using a wire feed welder due to the thinner wall thickness? You can still gets boatloads of capacity out of some 1/8" thick welds.

Good Luck

Yooper Dave

 

[hazmat]

<font color="blue"> Yeah but as your size increases, so does "c" in the numerator. So to compare two candidates in bending, compare bh^3 rather than bh^4.
</font>

Man the teacher busted us /forums/images/graemlins/shocked.gif

Thanks for catching our sloppy engineering. Hard to think straight when you've got tractoring on the brain /forums/images/graemlins/tongue.gif

Nice suggestion RE the angle, might give a larger "step" for the drivers to land on.

 

[hockeyhead]

If I understand this right, this is a "free standing" 30" ladder clamped to lip of a lowboy . first any of the materials described here will easily surpass your requirements. As far as the clamping to trailer that 3 pieces of welded flat stock and a couple of bolts appears to me to be your weak point. flexing, as a 350lb man climbs up and down. that same Ryerson catalog that spec. sheet came from has a large selection of "C" channel and such. Or a fab shop could brake something up.
My other thought was steel get pretty slippery when wet.
In rainy or winter conditions, slipping on a 1",or 1.5", square tubing ladder is going to hurt. round stock rungs would inprove this or brake up some 1/8 diamond plate for rungs, if employees or co-workers are going to use this you might want to look at some kind of traction control , just my 2 cents worth good luck with ladder

 

[trailertrash]

Even tho I've been on here (tbn) for a while it still amazes me with the amount of available info that is freely offered by the professional members and those with experience in what ever area that it is needed. Anyway thanks for everything and I'll check back with updates as soon as possible.

 

[rlw]

<font color="blue"> </font> "Yeah but as your size increases, so does "c" in the numerator. So to compare two candidates in bending, compare bh^3 rather than bh^4." <font color="blue"> </font>

<font color="black"> </font> Oops, my mistake. However, I think you meant to say compare c/I, where c is b/2. <font color="black"> </font>

Good point on the angle iron - I agree. I rarely use square tubing, almost always angle or C to help on weight.

 

[jmc]

"Do a weight calculation prior to fabrication. The self weight of your project can get pretty heavy in a hurry."

You'd be suprised at how many times I have relearned
this tip!

As far as bending, I subscribe to RonR's "Fat Guy Theory". There is probably some weight to be saved. The bigger risk is a defective weld. The steel will bend but probably not snap like a bad weld could.

What about using aluminum?

John

 

[jmc]

rlw,

"However, I think you meant to say compare c/I, where c is b/2"

Yes! Thankyou.

John

 

[gsxr1100]

hazmat & jmc:

Okay they beat me to it! Weird I did not think anyone remebered there stuff from materials. Comes in handy!

 

[TheKid]

I have to agree with Ron when he said </font><font color="blue" class="small">( I would more concerned with how it attached to the trailer so that doesn't fail or come undone and cause the ladder to crash down. )</font> I had a couple of ideas for making the mount stronger. Add an aditional brace that goes below your clamps and rests on the side of the trailer. Use a mounting system that slides over the sides of the trailer to lock it in place. I modified your original drawing to show you what I mean.

 

[RonR]

The big head

You guys keep agreeing with me I'm liable to get the big head!

Take care,
Ron

 

[keeney]

Do the trailers have stake pockets? If so, your mount could be a piece of rectangular section that slides down into one or two of those.