Wood Beam Extension

[bigmig]

I am working on a project (new construction) where I have 2 large Gluelam beams that run at 90 degrees to each other. One beam 'hangs' off the other. The beam end load is in the range of 13kips.
The problem I have is that the 'carrying' beam is not braced. It basically spans from support to support with a wood knee wall built on top of it, compliments of Mr. Architect.

I'm concerned about eccentricity rolling this beam. I don't want to try and "grab" it with my columns. Moment fixity in wood is something I don't really believe in, so I have scratched the idea of a monster moment connection that is basically a monkey holding its own tail.

As a solution, I thought about extending the incoming glue lam beam with a piece of steel that would rest on top of the 'carrying beam'. This would allow me to bear my load concentrically.
The attached sketch shows my concept.

My questions are as follows:

1. has anyone every done something like this with success or failure?
2. is there any concern about wood shrinkage v.s. the multiple rows of bolts?
3. is there any concern about cross grain tension? I tried to keep the bolts below the neutral axis.

The text book problem is pretty much this scenario but flipped 180 degrees....i.e. hanger rods on a wood beam, with the note to keep things above the neutral axis.
Prying action will be analyzed.

Thanks in advance.

 

[hokie66]

When you said the beam was hung, I thought you meant it was below the other one. As they frame in the same plane, why wouldn't a typical bolted connection work, with angles each side?

 

[bigmig]

I'm concerned that the eccentricity caused by a connection would cause the carrying beam to roll. I have nothing to resist that roll other than the incoming beam that is causing it.

 

[AELLC]

A Simpson hanger rated to carry the 13K would not induce as much torsion as you think, because the fasteners to the carried beam fixes the connector to the carried beam and prevents rotation.

How wide can you make the carrying beam? 8-3/4"?

 

[AELLC]

Specifically, a Simpson HGU or HHGU.

 

[molibden]

Normally you have many options on how to transfer shear force. Rotation could be an issue if you had really long span. Check deflection and maybe rotation if you modeled it in FEM software. Normally the beam itself provides lateral restraint to the other beam. In Europe we use a lot of these kind of connectors. And moment connections in wood are pretty much real.

 

[molibden]

Your connection is not ok in my opinion. By eccentricity you will not get much rotation, in my previous post I wrote about long span beam that deflects and starts to rotate the other beam. In some cases this could be a problem, but not because a joint eccentricity.

 

[msquared48]

If you use a Simpson top bearing hanger, or design one yourself, there should be no worries. This is a typical, everyday framing situation.

Mike McCann
MMC Engineering

 

[AELLC]

Give your Simpson rep a call and see if you can chat with their engineering department.

 

[bigmig]

I guess Simpson does do this every day, like msquared48 and AELLC pointed out. Sorry about my disdain for moment connections in wood. For some reason I see them as partial moment connections, based on real world lever arms. Combined with lack of quality control and fastener number I just see them as impractical for the common budget driven job, but this is based totally on personal experience, and I would admit I need to research that topic further.

 

[molibden]

bigmig, no worries, nobody knows everything. It's important that you question yourself on topics where you are not experienced. This way we learn new things. Wood is specific material that needs special attention especially with connections. But not only strength also durability.

Structural timber engineering

 

[hokie66]

You don't need a moment connection in order to brace the carrying beam. A shear connection will do, as it will take a nominal amount of moment, and that is all you need.

 

[Triangled]

Agreeing with all the above regarding the hanger connection.
If I understood the item correctly, you still need to design for compression face buckling of your carrying beam. I am not exactly sure what you mean by "knee wall" on top of your carrying beam, but the image that comes to my mind would not provide compression face bracing for your carrying beam. It seams to me your carrying beam, as it is, may be braced at three locations, ie both ends and at the carried beam.
By the way, shrinkage and multiple bolt rows is an issue. So is cross grain tension although I don't see that yet in your original sketch.
In your original sketch, it's hard to tell what's going on with your carrying beam beyond the carried beam..... Is at a hinge connection or a column connection or.?

 

[AELLC]

Another thing to help would be to wrap a long strap around to keep the carried beam tight to the carrying beam, assuming both beams are the same depth.