Glulam Connection Question

[dastuff]

Hello, I posted this question at eng-tips but haven't gotten any feedback so I thought I'd try here as well. Thanks in advance for any help.

I have done a few years worth of work with wood design but haven't seen this before. I am doing an inspection of an existing glulam roof truss to verify the allowable live load capacity of the roof. Per my model, the wood truss itself seems quite strong, but the connections seem to be having problems (the connections max out at 60-70% of the strength of the wood). I would typically consider the first image to be a 4-bolt connection but I can't figure out what purpose the two perpendicular bolts serve.

I've heard of various types of specialty wood connections but haven't regularly seen them used. Does anyone have information on what the purpose is of these two perpendicular bolts and if they help the will increase the strength of the connection.

Thank you so much for your time.

 

[engrstructural11]

Which "perpendicular" bolts are you referring to? I'm confused. You showed two different pictures of two different locations. That's a truss right? I imagine all the bolts are working to resolve the chord forces. Not convinced that the lack of symmetry will play a significant role in inducing torsional stresses.

They all look like pinned connections to me, but I also don't have much wood design experience.

<shrugs>

 

[engrstructural11]

Oh, I see the bolts you are referring to now. Interesting. My only thought is maybe they are fastened down tight to induce compression into the ends of the chord members. Not sure how off hand that strengthens the wood but maybe that has something to do with it.

 

[pwilliams]

The perpendicular bolts that have circular washers appear to be in place to reduce long-term splitting in the wood at the plate connection. They induce compression perpendicular to the grain of the wood and would keep wood splitting to a minimum. This is a very typical way of correcting wood splitting after the fact.

 

[engrstructural11]

The perpendicular bolts that have circular washers appear to be in place to reduce long-term splitting in the wood at the plate connection. They induce compression perpendicular to the grain of the wood and would keep wood splitting to a minimum. This is a very typical way of correcting wood splitting after the fact.

Kind of what I was thinking. Do you know off hand if this is covered in NDS?

 

[pwilliams]

The perpendicular bolts that have circular washers appear to be in place to reduce long-term splitting in the wood at the plate connection. They induce compression perpendicular to the grain of the wood and would keep wood splitting to a minimum. This is a very typical way of correcting wood splitting after the fact.

Kind of what I was thinking. Do you know off hand if this is covered in NDS?

I've not been able to find a reference in the NDS, however, this method is a "tried and true" method for clamping/compressing split wood. See "Structural Renovation of Buildings" by Alexander Newman, Chapter 8. It references this type of detail. However, the picture above appears to be using this method prior to splitting. So, my assumption is the designer was probably assuming that the wood will split over time with loss of moisture, especially in an attic environment.