Max point load on 2 x (6)(8)(10) Wood Beam

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gwrdriver
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Re: Max point load on 2 x (6)(8)(10) Wood Beam

Post by gwrdriver » Wed Mar 17, 2021 9:34 am

Come on guys, forget "rack", look at the illustration! Do you see anything that looks like a moveable, truck, or trailer-mounted rack or lifting contraption? It's a simple beam, with a single mid-span load, resting on load-bearing structure. No shock or impact load.

Richard, the first two things to determine are (1) do you have 750lb+safety factor load-bearing capacity in the end walls. There are a number of things to check to see if your existing structure will transmit this additional load to the foundation.
#2 is to check to see how much headroom (vertical clearance) will you have over the end bearing points. This will determine the maximum depth of the beam you can use.

Then you can start thinking size, and just as importantly the load support connection to the beam.

The fuzzy photo is of a lifting beam which I installed in my utility building. The span is 12ft with an anticipated maximum single-point load of about 750lbs, but with a maximum headroom of 7.25" (2x8s.) So I doubled up two existing outside 2x8 joists, and tripled the center one with structural grade lumber and added a 3"x 5"x 3/8" connecting steel angle to distribute the load and add lateral restraint. The angle is bolted through to a steel plate above. Extra studs were added directly under the triple, and both end walls rest on CMU foundation walls. Lifting tackle is rated for 2000lbs.

I haven't run the numbers on this arrangement, this could very well easily handle 2000lbs safely, but the max I anticipated is a 750lbs vertical load and based upon my experience this will git 'er done.

This is as an example only, not necessarily what you should do, but what I COULD do, given my existing conditions. YMMV
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doublereefed
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Re: Max point load on 2 x (6)(8)(10) Wood Beam

Post by doublereefed » Wed Mar 17, 2021 5:39 pm

Thanks all! Yes, I need to clarify. This is for a static frame that would be required to pick up the end of the beam. It will not be in a trailer under dynamic loads or anything like that.

My problems is... I had see the forestry forum calculator before, and even using their data (Doug Fir North for instance) I don't even understand the outputs. See below. I don't have the experience to tell me what those results mean vis a vis going to Home Depot and buying some 2x material.

I definitely appreciate the response on this. I can't be the only one who's ever tried to figure out how much a 2x will carry under a point load.
beam results 4.jpg

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Greg_Lewis
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Re: Max point load on 2 x (6)(8)(10) Wood Beam

Post by Greg_Lewis » Wed Mar 17, 2021 6:37 pm

Ah, much better. You might want to check out GWRdriver's recommendation of a laminated beam. I've heard that such a beam would be stronger than a similar beam of plain solid wood. An I-beam configuration might be just the ticket.
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rudd
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Re: Max point load on 2 x (6)(8)(10) Wood Beam

Post by rudd » Wed Mar 17, 2021 7:07 pm

OK, I'm still not exactly clear on this - you say:
"static frame that would be required to pick up the end of the beam" but you show a beam with a point load dead center.

I am not going to vouch for that calculator or your inputs.


IF that is what you are designing, the calculator you posted says OK if you can stand the deflection. It is between L/360 and L/240. It is going to deflect 4/10 of an inch, it could deflect as much as 1/2" and be acceptable for a roof.

IF you get a piece of wood with no defects. I had a RR bridge tie (say 10" x 10") break off at the end when it bounced gently on the ground while being transported. Getting a piece of wood with no defects is going to be difficult I think.
Were it me, and I had to use wood, I'd think real hard about that glulam (or a microlam) mentioned above, or at least say (3) structural grade 2x8's with plywood flitches, all glued and screwed together. Flitch being a continuous strip of plywood full depth between the timber members. Steel plate flitches were once pretty common before glulam and microlam came along.
Your bending stress is going to be highest in the center of the span. At the ends, shear will dominate.
Wood tends to fail in horizontal shear - the top is in compression, the bottom is in tension. At some point, the wood will separate lengthwise on the grain. Boom.
BTW, your ? x 8 beam will be 7 1/4" tall, not the 7.5 you entered. So you are already figuring 1.07 times the strength of the actual size.
Remember also that the resistance to bending varies with the square of the depth. I.E., twice as deep, 4 times the resistance to bending.
And, were it me, when I got it built, I'd load it to say 1.33 times the design load and see what happened, say 1000 lbs.

Addendum: something is off with that calculator. S=(b)(d squared)/6. I'm getting a slightly higher value than what the calculator says. Which would be in your favor, but lessens my trust in that calculator.

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Chris Hollands
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Re: Max point load on 2 x (6)(8)(10) Wood Beam

Post by Chris Hollands » Wed Mar 17, 2021 8:57 pm

The joy of forums - something that is quite simple turns into something extremely complicated .

My head spins looking at and reading the above .

If I was Doublereefer after reading some of the replies I would give up the hobby - I would be scared to lift anything using wood - LOL

Its strange wood has been used to lift heavy items for hundreds of years and still is but you would never know it after double reefer posted this .

-Double reefer go to a truss company or similar and pay for them to do a calculation for you - problem solved it wont cost much and your brain can rest

KISS - keep it simple -

doublereefed
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Re: Max point load on 2 x (6)(8)(10) Wood Beam

Post by doublereefed » Wed Mar 17, 2021 9:39 pm

Rudd, thanks for that. Imagine 1,500 lbs resting in the middle of a sawhorse. Thank you for interpreting the results for me. I'm going to go with triple 2x8s... and load it up slowly.

John Hasler
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Re: Max point load on 2 x (6)(8)(10) Wood Beam

Post by John Hasler » Wed Mar 17, 2021 10:33 pm

rudd writes:
> Addendum: something is off with that calculator. S=(b)(d squared)/6.
> I'm getting a slightly higher value than what the calculator says.
> Which would be in your favor, but lessens my trust in that calculator.

I get the same result the calculator does.

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Re: Max point load on 2 x (6)(8)(10) Wood Beam

Post by John Hasler » Wed Mar 17, 2021 10:35 pm

doublereefed writes:
> I'm going to go with triple 2x8s... and load it up slowly.

You'd do better with double 2x10s.

doublereefed
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Re: Max point load on 2 x (6)(8)(10) Wood Beam

Post by doublereefed » Wed Mar 17, 2021 10:59 pm

John, I'm going to go with double 2x10s! That square of the dimension thing I think, right?

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rudd
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Re: Max point load on 2 x (6)(8)(10) Wood Beam

Post by rudd » Thu Mar 18, 2021 9:05 pm

The thing about tall and skinny - if you consider that the top of the beam is in compression and wants to be longer, and the bottom is in tension and wants to be shorter, the easiest way for the beam to do this is turn sideways, AKA "buckle". I used to know how to figure that.
And yes, wood has been used to lift heavy things for a long time. Engineering was probably an educated guess at what it needs, then double it.
When steel fails, it goes into yield. It stretches a good bit before it gives up. This gives you an opportunity to say the expletive of your choice, and get out of the way, or out of the building. This is how we design reinforced concrete as well. Steel takes the tension, concrete takes the compression. You make the steel just a bit weaker than the concrete, so the big sag/cracks/etc will tip people off there is a problem. If you did it the other way, it would just go boom with no warning. Kinda like wood does.
And John, you are correct on the S calculation. I read 3.5 rather than 3.25 for some reason.

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Re: Max point load on 2 x (6)(8)(10) Wood Beam

Post by John Hasler » Thu Mar 18, 2021 10:18 pm

Restraining both ends should suffice to prevent buckling.

paralleler
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Re: Max point load on 2 x (6)(8)(10) Wood Beam

Post by paralleler » Sat Mar 20, 2021 2:32 am

My engine only weighs 350 pounds over a 7' span and a mechanical engineer friend ran the calcs and said I should use at least a 2x10. The big thing to him was depth (10", 12"), he said as you square that number the strength goes up rapidly. I really didn't want to drop the engine so I splurged for a 2x12 on top of 4x4s using brown wood. Using this rig I was able to remove and re-install an axel; it's also been handy lifting heavy items out of my pickup as well.

I'm really looking forward to steaming again for kids and families once this Covid thing tapers off. Happy steaming to all.
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