Short-span glulam moment frame design - is it a good idea here? 4

[nivoo_boss]

Hey everyone!

So I need to design a house and the client wants the interior to be spacious. The problem is, I'm not too familiar with timber design and I can't really decide if the frame I drew is even feasible with timber. So I came here to get some advice. My main problem is in-plane stability of the frame. I'm thinking of a moment frame with stiff joints at nodes B and D. I can choose the spacing of the frames myself, so at first I made a rough model with loads with a 4 m spacing and the largest moment in that joint was ~60 kNm. But the client would accept if I added a tension rod between B and D nodes as well, even though it would not solve my in-plane stability problem.

What would you suggest? Is it feasible to design these joint B and D as moment joints or would be some other form of lateral restraint better? As for the latter, a ceiling full of bracings probably is not going to do it with the client.

Some pics, the first one is my diagram with dimensions. The second one is from the architectural model - with red I highlighted the frame under question and with green end frames where some struts and ties might be possible to place.

Oh, and I work with Eurocodes.

 

[jayrod12]

That sure looks a lot more like a commercial building than a "house".

Rigid joints in wood are tricky, but I have seen them done. You may be better off trying to get some bracing in there, I've seen some elegant things done with tension rods.

 

[phamENG]

At that scale, steel clad with wood would be a better choice. If it were a bit smaller you might be able to make it work with steel joints, but even that would be questionable long term. Apart from tested sheathing applications, I've essentially given up on the idea of finding fixity in wood.

 

[dik]

Moments are the big problem. If you can develop your connections with metal side plates and glulam rivets, you may be able to effect the connection. I try to avoid moment connections with wood in particular.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[dik]

Just heard from my wood guy (I'm not so much into wood, and my classmate is an expert)...

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[DoubleStud]

Make BCD bent steel (angled and welded). They can wrap the steel with wood to hide it.

 

[driftLimiter]

Although I agree completely that wood moment connections are tough to accomplish, they are subject to long term issues, and pretty unconventional. I have seen some applications where designers have become comfortable with them.

1.) There is a solution that it used in some parts of the world with long steel rods embedded with epoxy into the timber. Link. To my knowledge this hasn't picked up much steam.

2.) I don't know the details of this one but I saw a straight up glulam PEMB a few years ago in Colorado.

I am terribly interested in this one if anyone knows anything more about this type of construction.

 

[dik]

Nice... I like it.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Aesur]

Take a look at arched glu-lam members, I believe you will have an easier time working with something like that rather than trying to create a moment connection at B and D.

 

[dik]

...and glulam arches are attractive, too.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[nivoo_boss]

Come on, I'm not the architect, I can't just turn this into an arch

Anyway, these moment connections are relatively common around here - I'm in Estonia. But in Northern America as I can see they are not that common. Some pictures from around here - often these circular bolt arrangements are used.

 

[EdStainless]

Glulam arches, like in almost every church built in the US in the late 1960's.
They are typically decked with 4" thick double T&G. Makes a very sturdy structure.
The idea of clad steel is a very sound way to go.
The other (last) option is your original with steel tie rods, the rods painted to match the ceiling in order to try and hide them.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[driftLimiter]

Here is an example of how the 'arches' could look like a frame still.

 

[dold]

@driftLimiter

Did you take that pic of the PEWB? Whereabouts in CO? Address? Maybe AHJ has an open web portal where we could find some drawings. And FOIAs are free. I am most intrigued.

From afar, it looks like they've taken the "just grab the entire end of the beam" approach for the upper part of the connection. I think I can see the edge of the knife plate in the column on the far right side.

And on the left side at the mezzanine, are those....wood braces?

 

[kostast88]

I second driftLimiter. This is the best you could do. Either frame options are doable:

However working with glulam the problem is always suppliers. You depend on what they can get, and how fast they can deliver.

If you go with moment connections then this is typically done with steel insert plates. Through bolts (lots of them) are used and local thickening of the section. Looks like that (span is similar to yours, height is not): Link

I find the moment connections above very interesting. But you need to know what you're doing. Speak to the suppliers, they know and they probably even design it for you. If you need guidance IStructE & TRADA have lots of info, including design of these. Other sources too.

I would provide steel rods in the out of plane direction. It would be stiff and elegant enough.

 

[dik]

I've not seen glulam arches done using steel plate inserts. Ones that I've done or have seen are always like the pix by drift... Even in 'paint' grade, they are quite attractive.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[nivoo_boss]

Thanks for the discussion.

I found some graduation thesis on frame design from TalTech here and it featured a reference to a quite comprehensive timber joint connection design worked examples document (

https://1drv.ms/b/s!AhAXWQl3Eo-Tk69s6pDSllsSkyyuQA?e=TpZMxn).

On page 86 there are examples for this kind of design frame corner design, I'm going to work through them. I'm thinking about the embedded steel plate at the moment. There even seems to be a formula to evaluate the rotational stiffness of the joint - I could use this in the general model in SLS.

 

[kostast88]

What dik says is supported by IStructE. They identify as moment connections only the following arrangements:

In my past discussions with suppliers they did mention the plate inserts as moment resisting. I guess we are on the semi-rigid connections universe, which explains the numerous bolts.

 

[driftLimiter]

@dik From my best recollection the site is located Here

Here is a close up of the frame:

And here with the bolts in red, bearing plates in blue, and knife plate in green.

The used what appears to be a greatly thicker region of the knife plate for the tension and compression zone of the connection. Shall we proceed to cyber sleuth the site ??

 

[driftLimiter]

@dik Says here they got the panels from Europe. Interesting indeed. Link