Tensile strength of a 3/8" threaded galvanized rod?

Machinery's Hanbook. Look up effective thread tension area and length of engagement of the threads. Apply appropriate safety factor.

Ted

So, according to

the area is 0.07 sq inch, and with say 35000 PSI we get

2450 lbs tensile strength.

That's good enough for my application (TWO rods suspending a chain hoist from a 6x6" by 8' timber above the ceiling).

i

Stress conentration at the root of the cut threads.

Jim

Ignoramus27412 wrote in news:cmd6a3$b39$ snipped-for-privacy@pita.alt.net:

Sounds like you want to hoist some heavy stuff, like engines. I wouldn't trust 3/8" all-thread, just from a seat-of-the-pants point-of-view (I needed practice with typing hyphens). I'd go a bit heavier, like 3/4". Life is short, pry a couple more bucks out of that wallet and get some real steel up there. That engine is gonna hurt real bad when it falls on your foot.

I want to hoist stuff, but not too heavy. I can pretty much guarantee that it will be always under 1 ton (2200 lbs). I don't think that I can load my attic joists with more, regardless of rod thickness. Since the beam holding the chain hoist will be supported by two rods, that's plenty of holding power. That said, better safe than sorry, I will buy

1/2" rods instead. I already bought the 6x6" timber, 8 foot long.

My immediate plans include buying a couple of military surplus generators, about 500 and 600 lbs.

i

Take a closer look. It's usually rolled, not cut.

Harold

Bolt Supply Shop carries grade 5 threaded rod which is much better than the hardware store stuff.

Ted

Are you _sure_ that thr load will be evenly divided? Have you considered shock loading? Things can drop their center of gravity a little if they shift in whatever harness is holding them.

Ted

It should be, logically. The hoist is attached to the steel beam in one point, it is pulling exactly downwards at all times. The rods will be symmetric around the attachment point, tightened and both would be exerting similar tension.

Anyhow, I will go for 1/2" rods just in case, 1/2" rods are extremely strong (2.25 times stronger than 3/8, at least) and even one will hold much more than I need. 3/4" (suggested by another poster) is not practicable as the hole in the beam would be too big, more than the width of the beam's "wing".

i

That seems right to me. I recall that the 3/8" threaded rod we buy at work is rated for 2000 lb load. Greg

On Thu, 04 Nov 2004 05:18:05 GMT, RoyJ vaguely proposed a theory ......and in reply I say!:

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To add more (or agree?) to that, galv rod is even weaker than plain or electroplated rod in mild steel. My reference places it at about 3/4 of the strength of plain mild steel for 3/8 threaded rod.

Heat effects? Galv thickness effects? Dunno. I would assume that at least, the thread as cut would be a looser fit until galved, with a very weak metal making up the gap.

So the 35-45 kPSI would be a good figure. The ref places Mild steel at

60,000 or thereabouts, but then derates the galv rod.

Then you need to know thread _length_ and it depends on what you are going to use it for whether you add a large or small fudge factor.

There is also ultimate (break) strength, and Proof Strength. The second is where the metal deforms. At that stage the nut has failed, although it may still "hold".

***************************************************** Have you noticed that people always run from what they _need_ toward what they want?????

On 4 Nov 2004 18:43:29 GMT, Ignoramus27412 vaguely proposed a theory ......and in reply I say!:

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What about the beam? I plugged in an 8' beam 6x6, supported bit ends, load 2240 lbf. I used Southern Pine (strong according to the programme) and found that with a ton, the beam would break. This does not allow for any safety factor. All it takes is for a load to snag on an obstacle as you are lowering it, then to drop off, or as Ted said, the slkp in a sling or whatever, and you have huge increases in load, even if drops only an inch or so. I would _definitely be looking at bracing that beam, with at least a "dolphin striker".

What your hoist can lift should dictate your supports.

And yes, what about the building joists? I would see pillars at the ends of the beam, for any serious load. Even pillars closer to the load, just either side, placeable at will to just clear the load. This both supports the building, and helps the beam.

Wing? This is a solid 6" by 6" beam?

***************************************************** Have you noticed that people always run from what they _need_ toward what they want?????

On Thu, 04 Nov 2004 21:11:37 GMT, Ted Edwards vaguely proposed a theory ......and in reply I say!:

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I don't think "much better" goes far enough! Hardware store rod is "much _butter_" .

***************************************************** Have you noticed that people always run from what they _need_ toward what they want?????

The beam would be supported by five joists. Not by two at the ends.

The use of the hoist is to hoist things off the bed of my pickup.

With the truck under the hoist, there is no place for supports.

The wooden beam is 6x6" square, it is going to be in the attic. The beam that holds the hoist is made of steel, about 2x2", and is shaped like letter T. It is underneath, parallel to, one foot below the wooden beam, and is going to be attached to the ceiling of the garage.

Wooden beam: above ceiling and joists Steel T beam: below ceiling and joists

The wooden beam would be connected to the steel beam's wings by means of 1/2" rods. One "southwest" of the hoist attachment oipnt, and one "northeast" of the hoist attachment point, 2" away. In diagonal pattern.

I bought the rods today at Ace Hardware, they are rated for 3,100 lbs each. I already attached the steel T beam to the ceiling with lag screws. They hold the beam for now, but later, 1/2" steel rods will be bearing the load, not lag screws.

i

On 5 Nov 2004 01:23:17 GMT, Ignoramus27412 vaguely proposed a theory ......and in reply I say!:

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Ah! a 2' length unsupported and also a cantilever support. A lot different.

Either side of the truck. Or even in the bed of the truck? Seriously. In all of this, the (_ceiling_ not roof) will be the weak part. Everything in a roof is designed to take weight on the _roof_, thus placing the ceiling beams in tension, not flexion. Maybe you need to at least "hang" the ceiling from the roof rafters.

If it's a real attic, designed for human occupation, then it should be a lot stronger than a simple ceiling / roof space. I don't know. We don't go in for attics in Oz much, as such.

You _may_ get away with several lifts like 500 lb. But if you get serious and lift more, remember all of this.

OK. Ta.

***************************************************** Have you noticed that people always run from what they _need_ toward what they want?????

Yep.

The joists look like they are the same as the ones under the floor of the neighboring bedroom. Spaced 16" apart.

Yes, thanks, I feel that what I have is good enuff. That's thanks to all great suggestions here, as I started off with a much more dangerous setup.

i