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structural wood glue

structural wood glue

structural wood glue

(OP)
My client needs to make a load bearing column out of maple that will be 3.5" x 3.5"
They can not get a 4x4 solid maple piece and so they are planning to make a "built-up" column.
They MIGHT go with 3.5" x 3.0" BUT... they don't want to use mechanical fasteners, they only want to use glue.
They have asked to use a structural glue (they are thinking Tightbond 2) along with as few fasteners as possible.

NDS indicate built up columns with nails and with bolts but nothing with screws. I'm a little concerned about nails in hardwood (although I don't know if that concern is justified)

Load is about 3000# (600 DL and 2400 LL)
Column height is 10 ft floor to ceiling.
There is no opportunity for bracing.

I'm interested in knowing if there is specific glue I can specify that will eliminate the need for mechanical fasteners.

Also interested in any insight about screws vs nails for hardwood. I'm thinking that either way (screws or nails) they will be pre-drilled.

For a 2) 2x4 column, NDS indicates 10d common wire nails at 6" o.c. alternating sides and staggered. If similar size finish nails could be used, maybe that would be acceptable but again, I'm not sure how softwood requirements apply to hardwood.

Ideas?

Thanks,
Steve

RE: structural wood glue

I have no idea how this idea works with code compliance and safety..

But I can tell you based on a LOT of woodworking experience that if the parts are properly prepared before the glue up is performed (pieces well milled, without twist or surface flaws) than the bond between them will be MUCH stronger with glue than it will with nails or screws. A laminated column will at minimum perform the same (possibly better) as a solid one-piece column would.

As far as glue selection, I would highly recommend Titebond III over Titebond II in an application like this- titebond 3 is slightly stronger than titebond II, about 10% or so. More importantly, Titebond III is Type-1 water resistant, while Titebond II is rated as Type-2.

RE: structural wood glue

Can you approach a glulam fabricator in your area to see if one can be fabricated? They use proper adhesives and fabricate to specs or standards so there is no issue with code approvals.

Dik

RE: structural wood glue

(OP)
Thanks jg and Dik.
Yeah, I can't figure a code compliant way for the GC to built it either.
They want to use #8 finish screws (like this http://www.homedepot.com/p/GRK-Fasteners-8-x-2-in-... ) .
I think that will be fine. Glue might not even be needed but NDS doesn't address using screws (only nails or bolts AND it is for softwoods only (I assume).
I'd feel much better with screws than nails in hardwood.

RE: structural wood glue

10 foot height is not too long, nominal 2x4 hardwood that material should be available from speciality hardwood companies in your immediate area. (They are here in north GA.)

4x4 nominal = 3.5 x 3.5 = (3.5 x 1.5 inch (nominal board) + 3.5 x 3/4 (nominal center board) + 3.5 x 1.5 (nominal board) = 2 glued joints for a final 3.5 x 3.75 square column.

Glue them up, consider using 2-part structural epoxy (slow-set to allow make up and clampping), with the clamps about every 12 - 14 inches apart. (Getting that many clamps may be more expensive than the wood!)

AFTER the glue/epoxy has set, drill out dowel holes (1/2 inch dia) all the way through and insert the dowels to maintain the vertial loads across all three vertical members of the column. If you wish, add 3x tension elements (stainless steel through bolts) near the top, middle, and bottom, but they won't really be essential. You will need to glue wood covers over the bolts (use countersunk holes) to hide the bolt heads.

RE: structural wood glue

I am guessing the client wants to use glue instead of mechanical fasteners because they don't want to see the fastener heads in the finished product? If so, you may want to propose two alternatives....wood dowels or screws/bolts in recessed holes with a wood plug at the surface. Is the column top loaded or side loaded? If top loaded, there will be less of a demand connecting the plies together since they will directly share the load.

RE: structural wood glue

(OP)
The "problem" is slenderness.
I need the plys to act compositely due to the l/d limit for wood

RE: structural wood glue

The rated strength of Titebond III is 4,000 psi, approximately 5x the strength of the base material.

Developing composite action even with wood glue doesn't seem to be a problem to me.

RE: structural wood glue

(OP)
Thanks but.....

Here's where I get bogged down:
#1 NDS doesn't address screws for a built up column and that is what they (and I) want to use.

#2 Code doesn't provide a clean way for me to say the GC can glue it up with this great stuff and it will be fine....

I just need to get happy with the lack of an ICC accepted strategy.
I will recommend Tightbond 3 but I can't go without the mechanical fasteners. Seems like a 1/4" dam. plug every 12" on each side might not be too bad.

Seriously though, thanks of the input.

RE: structural wood glue

Can you talk to the building inspector and let him know that you will be using Resorcinol Glue and that it is what they typically use for glulam construction and boat construction. The product is stronger than any wood you will likely encounter and is a waterproof adhesive.

The glue lines are less noticeable than other adhesives and are less likely to affect the finish. If clear finished, be careful with using any adhesives that may prevent finish from covering and will show up.

Dik

RE: structural wood glue

No. Screws, or lag bolts, develope their clamping force by FIRST creating a multitude of wedging (tearing and pulling) forces INSIDE the the wood beam you are trying to clamp together. Exactly opposite of what you want your long slender column to face before its compression forces are added by the deck load above.

A through bolt creates the clamping force FROM the outside towards the interior joint of the glue holding the glued joint together. It is much stronger than the screwed joint. And "just as ugly"!

A dowel opposes the different linear compression forces down the column as they act on the three different glued members by resitsting those forces in shear across many compatible wood fibers. it is your best reinforcement with least likely chance of changing its forces over time as the wood shrinks and expands with temperature and humidity.

RE: structural wood glue

(OP)
Dik,
Good idea about the glue.
I have suggested they start with 5" boards and plane (or thickness sand) them down to the right width.

Thanks again

RE: structural wood glue

That's what they do with glulam... regular dimensioned lumber planed down to remove the radii... and they use resorcinol typically for glulam... I'd glue as many lams as you need and run it through a planer. You may be able to source the adhesive at a marine supply place if not your local lumberyard. I used to use hide glue for wood construction and repairs... but never for structural related stuff.

Your local building inspector should be in agreement, and, if not tell him you will take responsibility for the adhesive use (you are anyway, doesn't matter if he agrees).

Dik

RE: structural wood glue

Polyurethane glue is another good option for glue (but messy). It is one of the few modern glues rated for structural us, and it does not creep like many other glues.

Another option would be to use a standard lumber column and flue on a thin maple veneer for appearance only.

RE: structural wood glue

Be very careful with moisture activated Polyurethane glue, the stuff is glue line sensitive, and the tensile strength falls off rapidly as the thickness of the glue line increases. If you use this glue , treat the preparation of the joint as you would for resorcinol glue.
B.E.

You are judged not by what you know, but by what you can do.

RE: structural wood glue

berkshire is correct. Personally, I'd avoid using polyurethanes for this application.

Dik

RE: structural wood glue

I personally use Aerolite 306 urea formaldehyde glue for structural jobs like that one it is gap filling and transparent, however I am having a harder time finding it in this country ( USA) . The MDF industry uses this glue and you may source it there, if not you pay through the nose at the marine distributors. . If you want a resorcinol then there is http://www.cpadhesives.com/woodworking-adhesives/d...
Or one pint kits can be found at some hardware stores , Cascophen took over what Borden used to produce. They now produce CASCOPHEN® ADHESIVE SYSTEM G-1131 a two part Resorcinol glue, which has fair gap filling properties.
B.E.

You are judged not by what you know, but by what you can do.

RE: structural wood glue

It has been a while, but a couple years ago I looked into structural adhesives quite a bit. If I recall correctly, very few adhesives did not exhibit creep. Also, almost all had disclaimers about structural use. I believe that polyurethane was an exception.

I don't typically specify using adhesives because I deal mostly with residential work where good workmanship and quality control are lacking.

RE: structural wood glue

Would they consider a manufactured column? Weyerhauser has a 3.5x3.5 PSL and LSL. I've always liked the look of those.

Please remember: we're not all guys!

RE: structural wood glue

For acceptance, you could always fabricate a second column and load test to failure.

Robert Hale, PE

RE: structural wood glue

Hardwood and resorcinol adhesive must be glued at elevated temperature - not room temperature. It will not bond properly if glued at room temperature. It is very different than gluing softwoods such as Southern Pune and Douglas fir. And yes, glued laminated hardwood is a very good option and the codes recognize the AITC Standard 119 "Standard for Hardwood Glued Laminated Timber" which falls under ANSI A190.1-2017

Andreas

RE: structural wood glue

Thanks LaminatedTimber... didn't know that higher temperatures were required for hardwoods... only used it for DougFir...

Dik

RE: structural wood glue

The glue I mentioned in my previous post can be used on hardwoods at room temperature i.e above 70* F. However it takes 7 days to reach full structural strength, although the glue joint can be un clamped and handled after 12 hours. If you are using urea formaldehyde glues be aware that Acid catalyzed glues exhibit better cross linking than alkaline cured glues.
B.E.

You are judged not by what you know, but by what you can do.

RE: structural wood glue

Thanks, berkshire...

Dik

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