My new spreader beam plan (visited steel yard)

Perhaps if you put your square tube sandwich on the bottom edge of the plate where the buckling risk is, and cut a couple pieces of the plate to sandwich and reinforce the center hang point.

Pete C.

I _could_ worry about Ignorant making the top triangle of the chain lower to save some money. I _could_ worry about Ignorant using some un-speced chain for lifting. But I don't worry, Ignorant can repair an angle grinder and has a crane-operating nanny, so everything will come out OK. :-))

Nick

Iggy,

Some time ago, we put in a new septic tank. The people who manufactured and delivered the tank, unloaded it with a spreader bar that had chains that hugged the round tank, which weighed about 2,000 lbs.

Based on what they used, I built one myself, out of some rectangular tubing. Although I don't remember the dimensions exactly, it was something like 2"x4"x0.25".

When we lowered the tank into the excavated hole, it worked like a champ. It flexed, but did not fail. We used it several times to lift the tank during leveling operations.

There is tremendous strength in mild steel.

Vern> This is a continuation of my effort to make a suitable spreader beam

Yeah, right!

Your ASCII art was quite clear. You have the square tubing on the neutral axis of your beam where the tubing will do the least good. Stress is greatest at top and bottom, the top being in tension and bottom being in compression. Things in compression can buckle if they deflect at all in that direction, because then only bending strength prevents it from buckling further as bending stress becomes even greater with increasing buckle. I would weld a two-tube sandwich on the bottom and one or two tubes on the top.

Some controlled experiments with the ends anchored while lifting on the center with your crane might be educational. Now *that* would be interesting! I'm not predicting failure, mind you, it really would be interesting to see what happens. It might work just fine.

Whatever you make Iggy, do a proof test first: lift four times the expected load, just to be sure that the just-built gadget is up to the task. Yes, four times - that's a typical albeit a bit low kind of safety factor. Something like a spreader has to be able to survive some abuse and neglect without collapsing one fine day.

Joe Gwinn

Actually, Nick. lbs are strength. Weight is force and the lb is a unit of force, just like the Newton. The unit of mass is the slug, which would be inappropriate. It is quite reasonable to quite a strength in pounds.

It might be more correct to specify _which_ particular strength is being referred to... Ultimate tensile strength, Elastic limit, crumple/collapse strength etc.

Mark Rand RTFM

The lb is used as both a unit of force and a unit of weight in common practice, so it's best to specify the intent if it isn't obvious from context. We buy commodities by the pound or gram or kilogram, measure pressure in pounds per square inch.

MathCAD uses lbf to connote force and lb to connote mass. It also recognizes kgf as 9.807 Newtons.

Strictly speaking, a pound is a unit of mass, but since we all have about same gravity, a poud has an equivalent of force.

yep.

i

I'm sorry when I'm nickpicking[tm]:

"strength" is vague. Maybe we are talking about tensile strength. It would have the unit N/mm^2 or Pa or lbf/inch^2.

Oh, strictly we are not talking about weight, but mass. That has the imperial unit lb (or lbs as plural, and grain and many many more). The SI-unit is kg.

The imperial unit for force (N, Newton) is lbf (pound force), not lb. Other units for force are dyn, and p (Pond).

Nick

Actually strictly speaking a pound is a unit of weight. Your weight changes during the day depending on where the sun and moon are in relation to you. It also changes depending on where you are as the local gravity varies from place to place. There is another unit, pound mass, for mass in the English system ( that the English are smart enough to have discarded ). Dan

I always thought the handwriting was on the wall for the English system when they called their unit of force the "slug." Somebody was telling us something. Maybe it has something to do with the English affinity for gardening.

The "poundal" is another novel English idea. Never place poundals among slugs. They don't get along.

-- Ed Huntress

I thought that the slug was a unit of mass and the poundal was a unit of force.

R, Tom Q.

Ah, yah, slug is mass, poundal is force -- leetle bit of force, something like 1/30th or so of a pound. Weird people, those English. 'Go out in the midday sun too much.

-- Ed Huntress

OK, enough of the pleasantries , let's get down to brass tacks - pounds. Are they units of weight/force or mass?

Can't be both, can they? That would be ambiguous. We all know that things in life are never ambiguous.

Ambiguously yours, Tom Q.

All three of you stay behind after class and write out one hundred times:-

1) The unit of mass is the slug. 2) The unit of force is the pound. 3) One pound is the force that is requited to accelerate one slug at 32.1740 ft/S^2.

:-)

The only advantage that metric has is factors of ten. Wouldn't it be wonderful if the second was just a bit longer and there were 16 inches in the foot, then g could be 32 and we would have a binary system.

Mark Rand RTFM

===================== And how much does the number of angles that dance on the head of a steel pin weight? Unka' George (George McDuffee) .............................. Only in Britain could it be thought a defect to be "too clever by half." The probability is that too many people are too stupid by three-quarters.

John Major (b. 1943), British Conservative politician, prime minister. Quoted in: Observer (London, 7 July 1991).

According to NIST, slugs and pounds are units of mass; poundal and lbf are force.

As I understand it, the slug was introduced in physics texts early in the last century as the unit of mass in the FPS system, in which the unit of force is the pound(!), thus confusing a couple generations of science and engineering students.

Ned Simmons

Umm That'd probably be easier to measure in steradians :-)

Mark Rand RTFM

Well, that depends on the mood of the Saxons & Jutes, doesn't it?

R, Tom Q.