# Triple 2x10 beam has twisted



## WillK (Aug 29, 2010)

So I previously mentioned an oops I made while constructing one of my 4 beams I am putting in for my post and beam project which is for replacing the stacks of concrete blocks holding up my 1917 house:

http://www.diychatroom.com/f14/error-while-constructing-new-triple-2x10-beam-125008/

I'm working full speed on this project for the next 3 days, I'm off work this week and the kids went to stay with my mom the rest of the week. I've got this beam complete except for the last 2 board, but one of the center boards is twisted and this is has affected the beam, it has straigntened some as I've clamped, glued and nailed it together but it's still visibly twisted.

The beam is resting on top of my 6x6 posts which are on the spread footings I've completed so far, I have the beam supported on concrete blocks on dirt for part of its length because I have 3 footings that are not poured yet. The whole beam is at least 2" clearance to the existing joists, I'm setting the beam in a position to support 2x8 joists which will replace the existing 2x6 joists.

So I'm looking for suggestions how to deal with this... I'm thinking my options are:
- Leave it as is (or figure out what the acceptable variation is)
- Shim gaps?
- Try to pull the beam straighter when I nail in the brackets securing it to the post?
- Let the weight of the house straigten it? (only bracket one side of the beam so the other side can rock down under weight?? dunno, this one sounds risky)
- Scrap the beam and start over?
- Any other ideas?


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## joecaption (Nov 30, 2011)

If the beam is twisted it will be of no use. It will try to tip and may fail.


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## titanoman (Nov 27, 2011)

That's one nice thing about micro-lams. They don't twist and are very uniform.

Sent from a Samsung Galaxy S2


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## More Power! (Aug 2, 2011)

WillK said:


> ... one of the center boards is twisted and this is has affected the beam, it has straigntened some as I've clamped, glued and nailed it together but it's still visibly twisted.


I was always taught, in wood working, not to try to fight with the wood--that the wood would always win in the end. If the wood wants to twist, and you prevent it by mechanical means (glue, fasteners) from doing so, it will destroy itself trying. You need those beams to do their job by playing to the wood's _strengths_, not by attempting to beat those very strengths.

Jim


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## abracaboom (Dec 27, 2011)

If those were the last three pieces of 2x10 left if the world, you could make the beam work by notching it square at every place it's going to meet the posts and joists. As 2x10s are rather cheap, I would get a new beam. You can find a use for that beam if you cut it into three or four pieces, each of which should come out fairly straight.


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## WillK (Aug 29, 2010)

abracaboom said:


> If those were the last three pieces of 2x10 left if the world, you could make the beam work by notching it square at every place it's going to meet the posts and joists. As 2x10s are rather cheap, I would get a new beam.


I'll probably do that then.. Aside from replacing this, last week I had bought all of the boards I needed to finish putting all 4 beams together. I don't think I had left a single 2x10 on the shelf at HD and Lowes that wasn't twisted or split. 

Sad thing is I'm sure the same boards will be there if I was to go again, although HD had an unopened stack of 12 foot long 2x10 which is what I'll need most for this beam since I have a lot of shorter spans (nominally 7' and an overall length of about 34', so normally I'd have 6 footers over the span, but this beam has 9 due to various obstructions.)



> You can find a use for that beam if you cut it into three or four pieces, each of which should come out fairly straight.


That is a very useful suggestion, I will be needing some more temporary supports as I get ready to dig footings for the last beam, so I'll be able to make use of sections of this beam for that purpose. Thanks for that idea.


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## WillK (Aug 29, 2010)

Okay. I have to ask because it's occupying my mind and distracting my focus.. Is there a particular amount of twist that should be acceptable? 

I'm an engineer, so I know perfectly well that there is no such thing as a board that will be perfect when it comes to being straight or twisted, and I know that visible inspection doesn't really give you a way of checking dimensions to a tolerance.

My objective for today is digging, so I'll be buying replacement boards and building beams tommorrow.

What I have is that at one end of the beam, it's visibly close to vertical. At the other end of the beam, the 2x10 at the top edge is roughly 3/4" to the left from a vertical line from the bottom edge.

I have no intention of saying this beam is good enough, I was iffy about it to begin with from my previous thread where I had put in a center board where it would be proud, plus I had made a measurement error which resulted in one of my joints being close to the edge of a post instead of centered over the post. So just to be clear, I am rebuilding this beam. I just want to know so that if I build another beam and I have a little bit of twist, I'll know when to cut my losses.


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## Daniel Holzman (Mar 10, 2009)

Generally I err on the side of caution. However, if the beam meets the specifications of the designer (I assume you had a designer, or did you do your own design?), some twist is likely not a problem at all.

Bear in mind that the strength of the beam is controlled by the moment of inertia of the beam, which is barely affected by twist. Several folks on this forum have pointed out that it may be difficult to get the beam to lay flat on the supports without chiseling or rasping the beam over the supports, however that is not very difficult, especially if the twist is not too severe. By the way, twist can be measured by degrees per foot, meaning for example if the beam has twisted 10 degrees in 16 feet, that would be 0.625 degrees per foot. Twist over 0.5 degrees per foot is high, but does NOT by itself affect the strength of the beam.

If you use Simpson brackets or similar, they are pretty tolerant of twist, as long as you rasp the bottom and top flat, the sides can be well out of plumb and they still work fine. Several of the joists I used on my deck twisted badly, they still worked fine in the brackets, and as I said, twist by itself does not affect strength.

There is another issue you should address. Twist is often caused by differential movement due to asymmetrical drying, or by the orientation of the grain. As has been noted by others in this thread, attempting to straighten a beam which has twisted can be difficult, and always results in large stresses on the beam which can cause additive forces on the beam which the beam was never intended to handle. In residential construction, beams are usually designed to handle vertical loading only, meaning they are designed for pure bending. Some elements such as rafters may be designed for a combination of bending and axial loading. In seismic country, major beams should be designed for bending, possibly axial loading, and transverse loading from earthquakes.

Residential beams are NEVER designed for a combination of bending and twisting moment. Note that a twisted beam which is not restrained carries no torsion (twisting) load. Sometimes people confuse the geometry of the beam (twisted) with loads on the beam, but the principal is that a beam which is free to twist will twist without adding forces to the beam. As soon as you restrain the beam against twisting, for example by attempting to jack the beam back to a straight condition, you add torsional loading to the beam, which in some cases can exceed the bending moment the beam is designed to carry. This is a very bad plan, and can lead to catastrophic failure of the beam.

A couple of caveats. First, if the twist has caused the beam to split, especially along the length of the beam, you should consider using the beam for firewood. If the twist is so extreme that either end of the beam is more than 20 degrees out of plumb, you should consider using the beam for firewood.

Conclusion: Twist by itself is a hassle because you have to flatten the faces to install the beam over the supports, and you may have to do a little shimming. As long as you do not restrain the beam, attempt to straighten it, or in any other way try to fight the twist, the structural strength of the beam is not likely to be compromised. Assuming the beam has not split, and is not so far out of plumb that it cannot be installed in the brackets.


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## WillK (Aug 29, 2010)

Yeah... So now that I cut the beam for removal I can see where the problem happenned. So there are 8 posts supporting it, I made my first cut after post #4 (the joint where the joint was going to be at the edge of the post instead of the center.) Once the post was cut, I was able to see a 8" long section where there was a gap between 2 boards on one side. At it's largest, the gap was about 1/4". The beam would be constructed from 10 boards had it been finished, I stopped after the 8th board was installed. 

A month ago when I made my previous post, referenced above, I stopped after putting in the 4th board. (Kids and wife have been taking up all of my time since Thanksgiving until the last week or so.) The 4th board is the board that has the twist. It's right in the blast path of the dehumidifier.

So I'll be using some construction techniques to try to prevent this from happenning again. Namely I'm going to build up the entire beam in one work session starting with building up 2 thicknesses then adding the third after the rest of the beam is in place. I'm also figuring on assembling 2 or more boards at a time flat then adding them to the assembly in place.

And yes, I am planning on using Simpson brackets to secure the beam to the post.

As far as what the engineer specified for the project... He didn't get into specifics about allowable twist, he specified a 6x6 post and triple 2x10 with joints centered over the post and staggered, and he specified a Simpson strap (with the words "or better") to secure the beam to the post. I'm using a Simpson post cap which over the phone I confirmed with him is better than the strap, I'm considering adding the strap in addition to the post cap. He didn't put a nailing schedule on the drawing, but I got that from him over the phone as well. I'm also exceeding the number of beams, and using smaller spans between posts than specified, and upsizing floor joists.

I've had the idea since that the remnants of this beam will actually come in very handy when I get to the point I need to lift off the original triple 2x6 beam (if it doesn't crumble away on its own that is)


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## Mills314 (Mar 21, 2011)

titanoman said:


> That's one nice thing about micro-lams. They don't twist and are very uniform.
> 
> Sent from a Samsung Galaxy S2


Agreed. I have seen this before and that was the fix that we used. Talk to your building department and they should be able to give you the specifics since the micro lambs are a bit stronger than store bought lumber.

They will be a bit more expensive, but you will never have to deal with it again.


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## titanoman (Nov 27, 2011)

I ask again. What's wrong with using micro-lams? 

Never mind this post. 
Thank-you.

Sent from a Samsung Galaxy S2


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## WillK (Aug 29, 2010)

Well, you see, the problem I have is that I would never be able to manuever a full-length beam into place under my house. This particular beam would be the closest to being able to do that, and I pulled a 20' span of my cut up beam out without crashing into anything, but for a full length beam I'd need to leave a gap at one or both ends right under an exterior wall.

My cost for rebuilding this beam will be $75 and I'll have it done before the weekend, those are both huge considerations - the latter more than the former.


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