Strength of 14 ga steel

[Ray Schafer]

I am building a weight lifting power rack. I want to add a lat pull-down. I have some cross beams on my rack which I want to use to lay a piece of steel across. I am trying to figure out how strong the steel is so that I know what I need to use.

At the BORG they have a square tube that has holes in it. I don't know what to call it. It is 1.25 in. square and 14 ga. and 3 feet long. It will be perfect if it will handle up to 300 pounds. I will never lift more than 200 lbs with it, but I am building for 300 to 500 pounes for safety.

Can anyone help me figure out the max load for this kind of piece of steel?

(I have thoroughly researched the building of a power rack with wood. Wood supports houses, and I have a great design. I am not looking for suggestions on whether I should do this or not, but I am happy to share my design and plan if anyone is interested.)

[Montgomery Scott]

The answer will depend on where the load and reaction loads are applied and the orientation and size of the holes.

The bending stress will be Mc/I assuming the beam is in pure bending. You can pull Ftu and Fcy allowables for the steel off the web.

[Ray Schafer]

I guess the problem is that I don't know what Mc/I means, nor do I know where to find Ftu and Fcy -- even if I knew what that meant. I only took one mechanics class about 28 years ago, so I guess I am a little behind the eight ball on this one.

Assuming that one end of the steel is at x=0 inches, that the steel is supported at x=0, 5, 31, and 36, that the load is connected at x=2.5, and 33.5 (two pulleys) -- how would I go about figuring it out?

The piece that I am talking about has holes on all four sides ... all over it. I could buy one of the solid square tubes and just drill a hole in each spot for the pulleys.

[Brian Effinger]

It sounds like a Unistrut. They use those in construction to hang things like pipe & conduit along with heating units, etc. I just checked their website, and I think their products would work, but I'm not sure about the borg knock-off. I'm picturing 14 ga. steel studs in my head, and those are pretty thick and strong, so I guess your idea would work, but I'm not an engineer - only an architect.

[Ray Schafer]

Brian, Please don't say "only an architect." Architects are people, too!

[Ray Schafer]

It looks like this, except that it has all four sides.

[Kevin Groenke]

according to this:
http://www.alliedtube.com/pdf/squarefit.pdf

The max allowable moment of 1-1/4x1-1/4x 12 ga is 4638in/ibs. Perhaps some engineers here would be able to translate that into joe-6-pack, but I'm inclined to think you'll be alright as long as nothing's cantilevered too far.

Unperforated is stronger, cheaper and probably nicer looking though less convenient You could save a bunch of $ by buying directly from a steel yard if theres one nearby. The borgs seem to mark up that sort of stuff 300% or more.
Somebody mentioned Unistrut, not what you're looking at, but might work...kinda erector set for big boys. There are some very nice extruded aluminum (AGAM for one) structural building systems out there, but they can get spendy in a hurry.

-g'luck

kg

[Justin Leiwig]

If you've ever been around a serious weightlifting equipment then you know that they don't use 14 gauge steel. 14 gauge steel is around 1.7 mm thick if I remember correctly. Also 1.25" square is too small to spread the load over.

Most of the power rack designs are either 2.5" square 12 gauge or 3" square 12 gauge. Go to the steel yard and get you some 2x2 box tube 3/16" wall. I think you'd be surprised to find that it will be cheaper per foot than the home depot stuff.

http://redeye.co30.com/rack.html

That's a good example of a decently built rack. I'm not sure about his "pipe" , but I would use solid steel rod to be safe. Olympic plates can do some serious damage when something goes wrong.

[Cliff Rohrabacher]

I guess the problem is that I don't know what Mc/I means, nor do I know where to find Ftu and Fcy -- even if I knew what that meant. I

Could throw Kilo inch pounds in the mix too and some stuff about the Moment Arm and energy developed with the speed of the weight shift.

I'd not use the perforated stock from the Borg.

Go to a Mill supply or steel company (Google is your friend) and order some heavy wall square tubing 2" in the side with 1/8' thick walls. Either that or, do what the weight lifting companies do - get a 1" diameter bar.

Is it 1" or 1.250'~? Whatever you can emulate them and prolly be just fine. If you plan to be drilling holes in it you might want it thicker.

[Brian Effinger]

Brian, Please don't say "only an architect." Architects are people, too!

I was going to say, "namby pamby, artsy fartsy, pretty boy architect"

[Ray Schafer]

Yeah, ok, I would have to agree with THAT!

[Chris Padilla]

My company just tossed up a new gym for its employees and filled it with some of the nicest stuff I've ever seen in a gym. I can say for sure that 14 gauge steel is no where to be found on any equipment in this new gym except for maybe placards on the equipment!

I'd go heavier if I were you...just my feeling on the matter.