strength of steel

[moto]

So I am new to working with steel. I hoping this is the right place for the questions. I am interested in building trailers. How does one know what thickness of materail to use. I figure the heavier the load copacity of the trailer the thicker the steel needs to be.

Is there a formulation or a standard thickness for certain load copacity?

Example. 2000 lb axle kit, 4' X 8' bed of trailer, 12"wheels How thick does the steel need to be. I figured in useing square tubing for the project.

[DSW]

Steel comes in various strengths. Most mild steel is A36 or 36,000 lb tensile strength. This is most likely what you will use for a trailer. Other steels like 4130 are used for high strength applications.

There are complicated formulas that engineers use to determine how much steel will hold based on the shape of the steel and how the loads are transferred. For a small trailer you can just buy a set of plans from Northern or go and take a close look at a trailer that someone else has designed commercially. HF has some small light trailer kits, Home Depot near me has some heavier 5000 lb trailer for sale you could look at.

Size and shape has a lot to do with how much load a steel member will take. A 3" C channel will bend long before a 12" tall 1" wide rectangular box tube would, even though the tube may be lighter in thickness. The fact that the tube is tall is what makes it stronger even though the material may be thinner. Think of it like a truss or like those ][ wood joists it's the design that make it strong not so much the material.

Most of those small 2000 lb trailer kits I see places like HF use thin 2x2 angle at best for a small trailer. You will need to keep the weight down. The axle, frame and bed adds up fast. In tube 3" x1 1/2" or 2 1/2" x 1 1/2" , 14 gauge or thicker should work fine for a trailer that small.

Remember when you decide to build a trailer that you plan to put on the road, you are accepting the responsibility to be able to make it strong ans safe. You must be able to make good solid welds every time. Good enough isn't good enough any longer. If you have even the slightest doubt in your skills DON"T. Get someone who knows to do it for you or at least get them to test your welds and inspect your work. Lives depend on this.

Good luck.

[triptester]

The thickness of the steel required depends on how the trailer is designed. A flat bed with no sides will require heaver metal. A trailer with ridged sides welded to the frame will form a truss allowing the use of much lighter steel.

An example; two semi-trailers one a flat bed the other an enclosed trailer. The flat bed will have two heavy deep beams to support the load. The enclosed trailer will have no support beams the full length of the trailer. The enclosed trailer uses the sides and top to form a truss to support the load.

When using tubing for a trailer care must be taken to prevent moisture from collecting inside. Sealing the ends often fails it is best to leave the ends open to provide ventilation.

I built a trailer some 20 years ago using all 2 1/2" x 1/16" wall square tube for the frame. The trailer was designed to carry 1 cubic yard of stone approx. 3000#.The only problem was the steel looked like swiss cheese in less than ten years.. I have since built a new frame using 2 1/2" x 3/16" square tube for rails with 2 1/2" angle for cross stringers. The capacity is the same but the trailer weight doubled.

[moto]

Thanks again for the help. I certainly need some more practice and I agree lives are at stake when putting a trailer on the road and wouldn't want the thing to fail.

Are there companies that inspect welds for these kind of projects or do you just find someone that does it for a living to check them out?

Do you recommened any books that would be able to help me with figuring out different designs?

Thanks again guys. So far everyone is nice and friendly willing to help the newbies.

[MoonRise]

moto,

Your question is what engineers figure out.

Because the question isn't really "what is the strength of steel?", but is more properly "Is this structure OK?"

Steel can have a strength of ~15 ksi (fatigue limit) to over 300 ksi (ultimate tensile strength), depending on alloy and heat treatment. The design limits depend on the material, and how the load is applied and transfered and resisted in/through the structure, and the environmental conditions, and the applicable Code requirements.

And if you don't know what ksi means, then designing a structure that will be out in the public is really past where you are knowledge-wise.

So the answer is, like many times to a broad and open question, "It depends."

If this is a small personal-use trailer for your own use, buy a set of low-cost plans from one of the trailer or trailer supply places. Or carefully copy a known 'good' trailer.

If you are trying to get into manufacturing commercial or heavy-haul trailers (because your statement of "I'm interested in building trailers" is rather open-ended), hire a design engineer.

[Craig in Denver]

Google "trailer plans", that'll keep you busy. Most will include a materials list, that will define steel choices (angle, channel or tube) and thickness.

"So I am new to working with steel. I am interested in building trailers."

Welding is harder than you think. Just welding a piece of steel on a table isn't easy. With a trailer, you'll have to weld straight up (vertical) and overhead. So don't think you can just buy a 220v welder and steel and build a trailer this weekend.

And a 120v welder isn't an option.

I love working with metal at a hobby level. Good luck.

[Teddco]

"How to Design and Build Trailers" - Vol 1 and Vol 2 by M. M. Smith

I'd go to a library and ask if they have these books to see if you can get what you need out of the books before I bought them. They run $25 each new. Like many of the previous posters indicated, there's some engineering and welding skills required to build one that works and won't fail in use. If you don't know how to calculate the moment on the axle stub that extends past the spring perch when the trailer static load is 3500 pounds, apply a safety factor to cover the dynamic loads and then buy axle material of the proper strength, then buy trailer plans and material lists approved by a licensed Professional Engineer or at least copy the materials and dimensions of a commercially sold trailer.

[moto]

Thanks guys! It sure put things in perspective. I do have a lot more to learn and as I am reading more and I am figuring out that there is much more then putting some metal together with a welder.

Sorry for the broad questions, I never realized how much went into it but it all makes sence.

So I will check out some plans. It would be a small utility trailer. I working on smokers and would like to put a trailer under one at some point. It would be about the size of a small utility trailer.

Thanks again!

[tresi]

Keep in mind that while rectangual tubing is easier to fit but making a trailer out of channels and angle iron will be cheaper and won't have built in water traps.

[andromeda]

I've been working with steel and welding my adult life, my advice is stop right now and buy a used or cheap new trailer. You don't have the regular welding skills, never mind about working with thin gage steel. You don't have the design skills to work all this out, and see around the corners.You don't have the experience to tell what works well with trailers and what doesn't.
If this was a stand or a rack in your backyard you would only injure yourself,but if this broke apart at 50 m.p.h. on the Mass Pike you could could kill a family.
I wouldn't do it and please don't you do it.
Thanks

[tanglediver]

So I am new to working with steel. I hoping this is the right place for the questions. I am interested in building trailers. How does one know what thickness of materail to use. I figure the heavier the load copacity of the trailer the thicker the steel needs to be.

Is there a formulation or a standard thickness for certain load copacity?

Example. 2000 lb axle kit, 4' X 8' bed of trailer, 12"wheels How thick does the steel need to be. I figured in useing square tubing for the project.

Manufacturers use standards that have been developed to make good economical sense. Custom trailers can be built to satisfy any specific need. Do you need just one trailer for a specific purpose?

To answer your questions in a nutshell, that's what engineers DO. Let them do the WORK for you by investing a bit of energy into finding a good set of sensible plans that are widely available, as suggested. At the very least, some plans will give you an idea of what can be done. You may decide on a simple used trailer, or not.

http://www.youtube.com/watch?v=jq-1ZSI0HzE