Glu-Lam beams delaminating

[Prestressed Guy]

I was asked to look that the roof beams of a structure built in the early 1960's which has Glulam beams @ 11' oc and 3" cardecking. The glulams did not have finger joints at the ends of the individual boards and at several locations the bottom ply was splitting off along the glue joint from the butt ends of the bottom board. I have attached a photo.
Have any of you ever seen glulams made this way?

 

[dik]

I've never seen a glulam that was butt joined like that. I would treat it as a member that had 1 or 2 less laminations. If the top joints are neat then they may function in compression, but, endgrain to endgrain is not normally good. You can use epoxy injection to seal any cracks and also 'patch' the end joints in the top and bottom lamination and any others you notice. There was a brief period of time when many glulam manufacturers used an adhesive that was not totally waterproof... and the construction may fall into that period. It may be that someone did their own glulamming... just don't know.

[Added] Glulam at that time was graded so that stronger material was on the outer fibres of the beam and typical strength was 2400 psi in flexural tension.

Dik

 

[IRstuff]

Are the delaminations at expected stress points? The outside joints are not supposed to placed at stress points.

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[Prestressed Guy]

The butt joint in the photo is right at mid-span and the rest of the beams are the same. The beams are 19'-6" clear span and 11' oc. DL = 15 psf and SN = 25psf. I calculate that it should be a GL5.125x13.5. The existing beams have 7 plies showing so it is only 10.5" deep and you have to ignore the bottom ply at a minimum. I had also considered that they may have been built on site by the builder.
My friend asked what the options are. I told him the best bet was to figure on at a minimum, removing and replacing all roof structure or look for another property.

 

[oldestguy]

Why not add steel plate straps underneath each beam, if possible? If glue seems to be failing, add bolts top to bottom for shear resistance improvement.

 

[dik]

It is possible to put a couple of C6's on each side with a bottom strap and secure the C6's to the glulam with glulam rivets and Bulldog adhesive or something of that ilk.

This can be repaired in place. Is the roof constructed using 3" T&G Plank? The glulam can be jacked up a bit to make it more level.

Dik

 

[Sawbux]

Looks like it may be "home made" glulam. Never seen a commercially made glulam with butt joints.
In the 60's, before finger joints, a lot of glulam were made with "scarf joints" and casein (Elmer's) glue.
I've seen a lot of glulam with separated scarf joints and some with failed joints - due to casein in wet or humid locations.
You could sandwich with steel each side or even glulams of LVL's.

 

[dhengr]

Haydenwse:
Of course, you want to shore the beams or the roof structure during the repair, to take much of the load off the beams during the repair. Otherwise, the beam will have to open up even more and deflect more before the bottom reinf. pls. even come into play and start to pick up a share of the loading, or tension loads in the bot. plys. You would also like to stress/stretch any splice pls., to get any slack out of the and out of the bolt or nail holes, so these don’t have to be taken up before the pls. start to pick up their share of the loads. You could also post tension the beams with harped rods on either side of each beam. The rods would have turnbuckles, a saddle of some sort at center span, and a pl. or channel or some such across each end for the dead end of the rods.

 

[IRstuff]

Perhaps it was DIY; likely the DIYer thought it looked nicely symmetrical to have the joint in the middle.

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[Prestressed Guy]

I came up with several suggestions for ways that the roof structure could be strengthened but part of the allure of this structure was the varnished beams and cardeck ceiling. Any ways that I could think of that would add the needed capacity would not be pretty. This same structural system is used for almost the entire 100' x 100' building

 

[dik]

There is no pretty repair. You may be able to split the glulams and insert an inverted structural T section or supporting cables. You can also reinforce it with a 'trussed rod' system installed on each side of the beam. You can make this look pretty and treat it as a feature. Other than that replacement would be the only other repair.

Dik

 

[Prestressed Guy]

The best part about this discussion is that my friend has not yet purchased this property so he can make his decision and any offer based on the knowledge that the entire roof structure is inadequate. He had planned on doing some extensive remodeling and the structure requires a complete re-roofing.

 

[IRstuff]

One other issue might if the glulams were correctly made, but overstressed, is why are they overstressed? Did a previous owner change the roof somehow?

An early 60s structure possibly had a cedar shake roof, which comes in at about 0.5 lb/sqft, dry. If the roof was subsequently converted to cementitious roofing, ala EagleLite, it'll come in at least 5.5 lb/sqft. For a 2500 sqft roof area, that's an additional 6.25 tons of roof loading.

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[dik]

Re-roofing is the least of his concerns...

Dik

 

[hokie66]

I had to use google to see if the term "cardecking" is for real. It is, but lots of folks were asking the same question. Most of us would just call it 3" T&G decking.

 

[Prestressed Guy]

Sorry for the regional term. In the Pacific Northwest, if you ask for 3" tongue and grove decking they say "Huh?". There are no drawings of the original construction but from what can be seen and measured the roof substructure is 2.5"x5" T&G decking with random layout over the 5.125"x10.5" glulams. They are built with all butt-joints in the plies and the joints nearest to mid-span all show separation and splitting at the but joint. From the outside it can be seen that there is about 4" of exterior foam board and some type of membrane or hot-mop roof. 15psf might be conservative but even at 10 psf it would need 13.5" beams even if they are actual 24F-V4 beams. With the failed butt-joint at mid-span they cannot be analyzed as more than 9" depth because the bottom ply is obviously not carrying any tension.