What causes a beam to have a preferred top orientation?
Glulam Beam - Checking Problem
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OP
Pettrix
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I believe it has something to do with some designed positive camber in the beam. So when the beam is installed, it goes from a positive camber to neutral once the loads are applied.
yooperdave
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The tension lams are the best material and put on the bottom for maximum strength. As noted earlier, the capacity of the beam is cut in half if installed upside down, as the compression lams do not have the strength. The use of LVL and PSL eliminates this issue.
OP
Pettrix
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So with the Simpson fully threaded timber screw with 2,000 lbf of tension and 1,400 lbf of shear strength per screw. That screw would be stronger than the original wood and bond glue, wouldn't it?
I am wondering if it would be a good idea to just run some of those screws in the other 2 beams as added security?
I am wondering if it would be a good idea to just run some of those screws in the other 2 beams as added security?
I doubt it. The tension strength is just the ‘squeeze’ of the boards together, not really adding anything to the strength in the direction the beam gets it’s strength from. The shear strength of the screw could add to the resistance of the boards passing by one another as the load is applied, but I doubt it is anything significant compared to the full glue-up of the assembly.
I’m surprised they don’t recommend injecting glue or epoxy in the check prior to driving the screws. That would be my fix.
yooperdave
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The glue transfers horizontal shear between the laminations so the member acts compositely. The new screw needs to now transfer the shear (if no epoxy). The shear can be calculated and compared to the allowable shear capacity of the screw.
And yes, the beam should be shot up with epoxy after the beam has been shored with a camber up. The epoxy will restore much of the integrity if performed properly. The screws will draw up the lams and close the cracks. The epoxy and screws will both transfer shear.
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ponytug
Super Member
I would not do it as a "just in case". Screws cut the fibers in the wood and that is damage. It can also provide a point or checking and cracking to originate from.
If you have checking concerns for the other beams, I would raise those concerns with beam manufacturer, and see what they recommend.
All the best,
Peter
rScotty
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A timber screw with a fully threaded shank as you show can only provide a clamping force to the area directly under the head - and that force is limited becase it cannot exceed the the compressive stress of the fibers it bears on. The force is farther reduced by the angle of head.
Think about it: a fully threaded shank CANNOT pull two pieces of wood together, and the head angle only hurts that effort.
That type of screw is a poor choice for the purpose.
I am afraid that you need to find some competent engineering help.
rScotty
OP
Pettrix
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I am going by with what the glulam engineer is advising. Should I try and find another engineer to see what they recommend?
I am not sure why would the glulam engineer design something that would fail. The liability would be high.
yooperdave
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Do NOT toenail. Predrill lead holes from the bottom and screw-up like a good politician. The epoxy should transfer shear. The screws will hold it together while the epoxy cures. Toe nails may not draw up and close the crack as intended.
Yooper Dave