Wood Laminated Roof Deck Cracking

[karimom]

Hello,

I am new here but hit a bit of a wall when working on this laminated roof deck. The deck is made up of a series of 2x4 and 2x4 wood laminated together using nails.

We were called in to investigate some cracking in the wood. I've attached some images. I ran the calc and it seems that the deck was properly designed based on the assumption that the wood is SPF No2

It leaves me to believe that the cause of the failure is due to material. One image looks like it was clearly shrinking/delamination and the other one could be due to a some knots in the wood but since its painted its hard to tell. The building is from 1955-1960.

I am just wondering if anyone else has any advice on what could be the cause and how to fix these cracks (i.e. some sort of epoxy or bonding agent) since removing/replacing them is going to be very difficult.

https://files.engineering.com/getfi...df-80e5-17e0582bb432&file=PastedGraphic-1.png

https://files.engineering.com/getfi...c8-950b-f6e361b4726e&file=PastedGraphic-2.png

 

[jayrod12]

I would be checking if the adjacent two 2x6 have the capacity to not do anything structurally and then just perform a cosmetic fix.

 

[karimom]

They are 2x4's laminated beside 2x3's. Since the grade is unknown it makes it difficult to determine if they are adequate. Assuming northern pine (weakest grade), the adjacent 2x3's should be able to take the load. Also, since the break is close to the edge, the amount of bending on it is less. I would assumed it would have failed in the middle if it was a structural failure.

I am thinking of using an epoxy (wood epox product) and then putting a small nailer plate on the bottom to reinforce it.

Does my logic make sense on this one?

 

[jayrod12]

I'm more partial to screws up through the crack, pre-drilled for the portion below the crack with washers. That plus some epoxy should pull it back closed.

 

[karimom]

Do you have any explanation for the crack as well? I'm still stumped on why it could have cracked? If it was due to overloading, the other members beside it would have also cracked. The crack (main one, not the one I believe is from shrinkage) is 2' from the support. The total span is 11'. I would have assume if it was bending (which shear is not a question) it would have been in the middle.

 

[jayrod12]

Likely a knot or something started it. It's also old so drying and shrinkage plays a part.