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4 ply 2x12 Beam Sag

pboneox1's picture

I am looking for some advice on how to strengthen in place a 4 ply 2x12 beam that is spanning 16 ft and supporting the second floor joist.  I have had an engineer do the calcs and the beam is sufficent to cover that span but still has a 3/4" deflection in it.  I am trying to figure out what I should do, I guess it is possible that it was just crowned improperly and it will not have any problems going forward but I am not sure I am ok with just leaving it as is since I am installing a kitchen underneath it.  The beam is currently nailed together (has gaps between the 2x12) and spans from the exterior framed wall to a block wall inside the house.

I am open to hearing any thoughts or ideas.

Thanks for your help.

p (post #207211, reply #1 of 28)

Can your upstairs take jacking up the middle of the beam to eliminate some of the sag?

If not, and you wanna leave it as is..........

Flank each side with something that's straight. 

I take it you know the sag is real and the upstairs then has fall towards the middle of the beam.  If you can get some of the sag outta the beam, flank it with a couple LVL's.  Bolt all together and remove the jack.

 

You might want to pre-bolt what you got, not sure on that, b/4 you add to the sides with LVL's.

A Great Place for Information, Comraderie, and a Sucker Punch.

Remodeling Contractor just outside the Glass City.


http://www.quittintime.com/

 


Beam Strength (post #207211, reply #2 of 28)

And it should be noted that beam width is far less of a factor than depth.  THe resistance to bending goes up by teh SQUARE of the depth.  A 2x12 has about twice the bending resistance as a 2x10.  So going from 3 2x12s to 4 does not do as much for you as one might think.

This is just for interest sake, and not intended to be very helpful to this repair.

That said, I am amazed how strong wood is.  I know of a 16 foot garage door header made of 2 2/12s and 1/2 plywood, which supports the ends of 26 foot spanning trusses.  This is in heavy snow load country as well.  IT does have a sag in it (not measured it) probably 1/2 to 1 inch.  Pretty amazing.  4 2x12s would be nearly 72% stronger in resistance to bending.  I suppose on difference is the floor beam is largely dead load and the garage header has to handle a fair dead load and a significant (temparory) live load.

The general rule of thumb for (post #207211, reply #3 of 28)

The general rule of thumb for a beam is one inch of depth for each foot of span. So your 2x12 beam is pretty thin to start with.

 

You say he calced the beam and it had 3/4" deflection in it.  Is that live load deflection, or total load deflection?  Big difference.

Also - What loading did he use?  Some only use a 30# live load for 2nd floor sleeping rooms in order to skimp by.

 

How much is it actually deflecting?

 

There's no real way to strengthen it in place, unless you can scab a deeper LVL beam on each side or add a center bearing.

You could replace it with something deeper.  If headroom is a problem a steel beam might be best.

Deflection Amount and Plan (post #207211, reply #6 of 28)

I did not mean to imply that the engineer provided me deflections, I was saying the deflection of the actuall beam at its deepest point was almost 3/4".

The plan I came up with to help strengthen the beam was to jack it up and add 1/4" x 11" plate on each side and another 2x12 outside of those and bolt it all together (so it would be like a giant double flitch plate beam). 

Any thoughts on this plan.

It's possible that you could (post #207211, reply #4 of 28)

It's possible that you could jack the sag out then install a steel flitch plate  on each side but run it by your engineer first. If not and it were my house I'd pul it out and install a steel beam.

Florida Licensed Building Contractor, 40 years experience in commercial remodeling, new homes, home remodeling and repairs and all types building maintenance.

I ain' no engineer but.... (post #207211, reply #5 of 28)

It could be that the beam is sufficient for the load but sagged in it's early life before it was actually properly dry. I have used plenty of framing lumber that was still suspicously heavy or easy to sink a nail into that was marked 15% MC. Some where a little north of that MC lumber can crown down easily before finishing the drying process. 

.

Oldhand, If this is the (post #207211, reply #7 of 28)

Oldhand,

If this is the case would you leave it as is or try and jack it up and add support to try and eliminate the sag.

can't see it from here... (post #207211, reply #8 of 28)

Sounds lke a good candidate for leaving as is.

.

Draw Back (post #207211, reply #11 of 28)

Is there any drawback or potential damage I could do to the beam by turning it into a flitch beam.  I got a great price on the steel plates as I know a metal supplier so it would be minimal cost and some labor on my end.

On a side note I was thinking of framing the beam in old barn wood so it looked like a actual exposed beam once I figured this out and that would be easier to do if it were straight.

 

Thanks for all the input!

Flitch plate beams are (post #207211, reply #19 of 28)

Flitch plate beams are neither fish nor fowl. One element doesn't contribute much to the other. In loading a flitch plate beam, because of the vastly different properties of wood and steel, the steel must be loaded about to the point of failure before the wood takes any significant load at all. The wood serves only to keep the steel in its proper orientation. I think they are a waste of time and effort.

You have some excellent suggestions above, both in replacing your existing beam with steel and in leaving it along and shimming the joist straight.

Here's another idea:

Add a flange below the existing beam. First, raise the joists that are loading it with a temp wall. Then cut a good 2 x 8 to fit between your end supports. Slather the top of it with thickened epoxy, (precoat the mating surfaces with unthickened epoxy)  Fasten it to the underside of your beam in three or four places. Raise this assembly to wherever you feel comfortable, just above straight would be good (like Calvin said, pay attention and don't raise the ends of the beam). Then fasten the hell out of it. Leave it for long enough for the epoxy to cure fully. Remove the various supports.

Note: a good 2 x 8 for this application would probably be one with a bit of a wany edge for as much of the length as you can find. It would be all sapwood. Avoid anything that contained the pith.

Ron

12 inches is not very deep (post #207211, reply #9 of 28)

12 inches is not very deep for a beam, and some sag would be expected over 16 feet even if the beam is in theory correctly sized.

When I replaced the sagging double 2x14 beam over my garage door with doubled 13" microlams I first let the load down on the beam, measured deflection, then raised the load again and inserted shims to compensate.  I believe it was about 1/2" in 16 feet, with just a roof load overhead.

(As a result, I have the only garage in the neighborhood where the garage door opening isn't visibly sagging.)


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

So would you leave the sag as (post #207211, reply #10 of 28)

So would you leave the sag as is or try and jack it up and add support to prevent the sag?  Unfourtently for me the people who built this house did not plan for the sag and so I have a floor and exposed beam that look bad (and I hope looking bad is all it is and not structually bad as well)

If you shim above the beam (post #207211, reply #12 of 28)

If you shim above the beam and then wrap it then the floor will be flat and the beam will look straight.


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

That was my thinking (post #207211, reply #13 of 28)

But first, someone needs to do the calculations to determine if the existing beam is adequate to support the imposed load and that the existing deflection is less than or equal to that allowed/expected for this beam design.  If it is structurally acceptable, I would at least eliminate the afore mentioned gaps by  bolting it together to make sure it fuctioning as a single unit.

Jack and Shim (post #207211, reply #14 of 28)

I did have an engineer tell me that the beam was adequate for my loads and that the allowable total load deflection was 13/16".

 

That being said if I am going to go to the trouble to jack and shim the floor joist and bolt the current 2x12's together why would I not just jack up the main beam and bolt some steel or lambeam to the exposed section (they additional pieces would not sit on the bearing sections, but should not have to in order to stop sag) as well to help stop the deflection?  If it is just a question of extra work I dont mind spending a little money and time for piece of mind.  Is there any damage that could be done to the beam by jacking it straight? 

By the way really apreciate all the help and insight!

pb (post #207211, reply #15 of 28)

There's potentially more to it than "jacking" up the beam.

First, you need a secure, firm, well supported place to put the jack.  It is always possible to jack down the area below what you want to jack up.

And, slow and easy with monitoring all the points of connection up down and around is something you should be aware of.

I've seen cases where the deflection was a poorly crowned joist or beam and jacking the middle to remove the dip, ended up lifting both ends.

Work your way up from below what you intend to lift and take all precautions necessary to do as little damage correcting the problem.

A Great Place for Information, Comraderie, and a Sucker Punch.

Remodeling Contractor just outside the Glass City.


http://www.quittintime.com/

 


I still ain no engineer, but..... (post #207211, reply #16 of 28)

It would be an interesting experiment but I'd be surprised if a well seasoned beam that size was flexible enough to be straightened with jacking up.

My guess would be that would actually weaken the beam itself.

If the deflection was noticeable topside the joists could be shimmed to in plane, and trimming the thing straight for appearance on the bottom side should be pretty easy.

That is assuming that the beam is sufficient for the load in the first place which is, we believe, previously established. 

I doubt I'd want to, uh, jack with it.....

 

.

boy, (post #207211, reply #17 of 28)

Two geezers (if your screen name is to be believed)

minds,

run in the same ditch.

Stop the sag, jack the joists and shim solid.

 

Call it done.

 

 

Now, if the op wants some barn siding info,

I'm a specialist.

 

 

to a certain extent..........

-bag of weed and a barn-we learned on the job.  That's what got me started in this exciting learning experience.

 

Wished I had absorbed more over those years, I'da been somebody.

 

 

 

]

but there I go-digressing again.

A Great Place for Information, Comraderie, and a Sucker Punch.

Remodeling Contractor just outside the Glass City.


http://www.quittintime.com/

 


I've been trying to stop the (post #207211, reply #18 of 28)

I've been trying to stop the sag for about 20 years now.  It ain't working.


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

3/4" deflection in 16' is not (post #207211, reply #20 of 28)

3/4" deflection in 16' is not that unusual, especially if the wood was not kiln dried. The typical allowable deflection for that span with live and dead load is 0.8". Wood moves forever so some additional deflection will occur. Sistering with engineered lumber or steel are both good options. I have used both options before. When using steel I have used structural channels because they are more efficient than plate. Flitch beams work, but the key is that the steel should be bearing on the support. Otherwise the stresses must be transferred from the steel back into the wood at the supports, which takes a large number of bolts at the ends. The engineer easily be able to design this repair .

user (post #207211, reply #21 of 28)

Typical allowable deflection in 16' us 8 tenths of an inch? 

no kidding?

To me, that framing would be way undersized.  Where'd you come up with this number?

thanks.

A Great Place for Information, Comraderie, and a Sucker Punch.

Remodeling Contractor just outside the Glass City.


http://www.quittintime.com/

 


Typical allowable deflection (post #207211, reply #22 of 28)

Typical allowable deflection for dead load plus live load is L/240. 16x12=192/240=0.8. For long beams its better to limit deflection to say 1/2 inch instead of using the above formula. 

Really? (post #207211, reply #23 of 28)

So you got a floor built to 360 and the beam is allowed at 240?

I'm assuming you are an engineer or perhaps an inspector (or one heck of a framer).

 

Gives new meaning to build better than code.

A Great Place for Information, Comraderie, and a Sucker Punch.

Remodeling Contractor just outside the Glass City.


http://www.quittintime.com/

 


The whole deflection ratio (post #207211, reply #24 of 28)

The whole deflection ratio thing can be confusing.  Rather than type an answer here I decided to start a whole new thread about it:


http://forums.finehomebuilding.com/break...

Thanks, (post #207211, reply #25 of 28)

I did some google study and found I don't know squat, but what did appear was less than an inch-ok

more than an inch-unacceptable.

A Great Place for Information, Comraderie, and a Sucker Punch.

Remodeling Contractor just outside the Glass City.


http://www.quittintime.com/

 


4 ply 2x12 Beam Sag (post #207211, reply #26 of 28)

calvin wrote:

So you got a floor built to 360 and the beam is allowed at 240?

I'm assuming you are an engineer or perhaps an inspector (or one heck of a framer).

 

Gives new meaning to build better than code.

 

I am an engineer. The L/360 is for the live load deflection (typically 40 psf load) and the L/240 is for total deflection (live load plus dead load (typically 40+10, or 50 psf). These numbers go back many years and were based upon limiting deflection to limit cracking in plaster. They have worked over the years so they are still widely used for dimensional lumber. But with long spans the deflection can be quite a bit. Nothings says that you cannot design better than code minimum and limit deflection to a more reasonable number.

With I joists and trusses long spans sometimes result in bouncy floors (vibration). L/480 is often used with these to make the floor stiffer. Some manufacturers (Trus joist) have programs that rate the stiffness of the selected joists for the span and you decide based upon their rating how stiff you want the floor. There ratings are based upon the percent of people that find the stiffness acceptable. Its a bit of a guessing game as to how stiff you should make the floor. 

Thank you (post #207211, reply #27 of 28)

 for the explanation and for qualifying your credentials.

Appreciate it very much.

A Great Place for Information, Comraderie, and a Sucker Punch.

Remodeling Contractor just outside the Glass City.


http://www.quittintime.com/

 


One thing I think isn't (post #207211, reply #28 of 28)

One thing I think isn't always very clear when talking about beam spans is that there are (at least) five different issues:

  1. What won't fall down
  2. What will be sufficient to prevent hypothetical cracking of hypothetical plaster
  3. What is "comfortable" to walk on -- doesn't feel unsteady
  4. What looks good -- the eye doesn't detect sag
  5. What code sez

Code attempts to embody the first four to a degree, but simply meeting code is often not sufficient, especially for #3 and 4.

On the other hand, there are many (especially older) homes around with beams that are woefully undersized according to current code but which are in no danger of falling down -- the L/360 standard is addressing #2 and 3 more than #1.


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville