Maybe switch to steel?
H-beam or pipe...
H-beam or pipe...
Replacing everything becomes very complicated, so I prefer to avoid that. Where can I find material data for plywood?
I would argue that plywood is a less optimal alternative.
Why not glue on knot-free wooden boards, one on each side?
How much space is there to work with?
Do you have any idea how much the column's I needs to be increased?
Why not glue on knot-free wooden boards, one on each side?
How much space is there to work with?
Do you have any idea how much the column's I needs to be increased?
You're probably right about the plywood. I haven't calculated how much I'll need yet, but I have no surface area constraints, it's purely about aesthetics. Ideally, I would replace the whole thing with an H-beam, but I can't see how I could get it in place without it needing to be a bit too short. Could a U-beam in steel that is placed around the existing pillar and bolted through be an option? Annoying as hell to plaster, but you could leave it exposed.
If the flanges cover at most half, you could place a beam from each side.
I just wanted to update the thread with this information I found about composite columns: http://www.diva-portal.se/smash/get/diva2:1034763/FULLTEXT01.pdf
Quite interesting reading. In chapter 3, it is stated that if you only have a nailed joint between the composite parts, you still achieve 55% of the bending stiffness of a perfectly glued column, which is considered to have the same strength as a solid wood column of the same dimension. I am leaning towards gluing the column and then screwing + clamping to get the best possible press pressure. What kind of glue should I use?
Quite interesting reading. In chapter 3, it is stated that if you only have a nailed joint between the composite parts, you still achieve 55% of the bending stiffness of a perfectly glued column, which is considered to have the same strength as a solid wood column of the same dimension. I am leaning towards gluing the column and then screwing + clamping to get the best possible press pressure. What kind of glue should I use?
Then I'll answer my own question here again about glue. If you use a PU glue like this one http://www.bostik.se/Products/Adhesive/Wood-adhesive/P0417, it has higher shear strength than both the glue used for laminated wood production and the wood itself. So if you're just a bit careful, you should be able to achieve close to 100% cooperation in the column. Thoughts on this?
PU-glue requires high press pressure, the foam that forms has very low strength. I tried a few different glues before I made up my mind, I finally used regular Sika outdoor glue, glued and pulled together with decking screws, no gaps and holds together like a solid post when sawing into them.Karl_Pedal said:
Aha, is there anything to read about how high the pressure needs to be for it not to foam? And what shear strength does the Sika glue have?Peter2400 said:
That would be 0.2 MPa if I'm not mistaken. With nail bonding, you might reach around 0.02 MPa, but I don't know how high you can go with screw bonding, so maybe it's just best to skip the PU gluing. However, I can't understand how PU glue can be sold in small tubes if it requires a hydraulic press to use it.
As you say, shear strength isn't really that important as long as it is 4 MPa or higher (since that's what C24 timber can handle). So, I mainly want to ensure that I get a glue joint that's stronger than the wood. Additionally, my composite post should strengthen an existing post that isn't 100% even, so it would be beneficial to use a glue that can accommodate some filling of minor irregularities.
Now I've read a bit more on Sika and I'm not getting any less confused. Regular SikaBond 530 (wood glue) is stated to have a press pressure of 2-4 kg/cm² while SikaBond 545 (PU) has no press pressure specified.