Integrated Buildings & Structures

Despite increasing scale and scope of mass timber construction, we are still relying heavily on steel and concrete for lateral load resistance in wood buildings.  Timber braced frames have now been implemented in contemporary buildings and have strong historical precedent.  One system that I haven't seen discussed is a mass timber moment frame.  Perhaps there is good reason for this, but let's entertain the thought.  There are certainly instances where architects might want the openness of a portal frame in timber.  Do you think a timber moment frame is possible?  What are some technical concerns that would need to be addressed?

Here are a couple that come to mind:

 - Connection slip amplified over the depth of a beam or column could result in large rotations before engaging an attached member.  Anyone who's checked story drift on a light-frame shearwall with an unfavorable aspect ratio knows NDS can be very punishing in these applications.
 - Orthotropic properties could cause issues transferring moment between horizontal and vertical frame members. - Long-term cross-grain shrinkage could result in loss of restraint as bearing surfaces which are initially flush pull away.  Perhaps some sort of take-up device could be developed to prevent this?

Eager to hear everyone's thoughts!

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Christian Parker P.E., M.ASCE
Structural Project Engineer
Washington DC
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Hi Christian, Definitively, timber should be a material to be considered more widely soon. Here I found this interesting video of what is being made in the USA: https://www.youtube.com/watch?v=gEewgo99tRc

The European experience (https://www.youtube.com/watch?v=x6JTJWY_uag) and East experience (joint or connections: https://www.youtube.com/watch?v=OJ8V_rzwxh0) should be noticed.

Regards,

AG

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Andres Guzman D.Eng., MEng, Ing., M.ASCE
Associate Professor
UNIVERSIDAD DEL NORTE
Barranquilla
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Hi Andres,

Very interesting.  We actually specified a Simpson Strong-Frame similar to this example for a small retrofit project, and it's true that this is more or less a timber moment frame.  One thing I notice looking with fresh eyes is that the moment transfer is achieved by overlapping the members and using an in-plane group of dowel-type fasteners, which is a great way to minimize shrinkage issues and connection slip, but would become less effective relative to the member capacity with increasing member width.  On the scale of glulam beams and columns that we might see in a mid-rise or taller timber building, this could be quite limiting.

The castle joint you shared is a really clever piece of craftsmanship.  My concern with this type of connection is that eventual cross-grain shrinkage would introduce play before the connection becomes fully engaged.  I've seen this on a project in fact: old, beautifully crafted joints between large timbers separated over time, resulting in substantial reduction in bearing area at the joint and considerable rotational flexibility.

This castle joint reminds me of East Asian dougong joinery.  There are temples, halls, and pagodas using this system that have withstood storms, earthquakes, floods, and more than a millennium of wear and tear.  It would be very difficult to justify drift and p-delta effects against a modern performance standard.  And yet, the performance is there.

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Christian Parker P.E., M.ASCE
Structural Project Engineer
Princeton NJ
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Original Message:
Sent: 03-19-2023 10:05 AM
From: Andres Guzman
Subject: Mass Timber Moment Frame

Hi Christian, Definitively, timber should be a material to be considered more widely soon. Here I found this interesting video of what is being made in the USA: https://www.youtube.com/watch?v=gEewgo99tRc

The European experience (https://www.youtube.com/watch?v=x6JTJWY_uag) and East experience (joint or connections: https://www.youtube.com/watch?v=OJ8V_rzwxh0) should be noticed.

Regards,

AG

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Andres Guzman D.Eng., MEng, Ing., M.ASCE
Associate Professor
UNIVERSIDAD DEL NORTE
Barranquilla
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Check this out

https://www.skyscrapercentre.com/building/projekt-pi/39979

Greetings

Olaf

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Olaf Faber P.E., M.ASCE
Senior Engineer
Zuerich
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Thanks, Olaf!  This looks really neat.  I had some difficulty finding English language info on this, but I gather that they are engaging the perimeter columns as part of the lateral system.  Do you know whether they are actually putting shear and moment into the columns, or using them as outriggers with axial only?  I'm curious about the connections and the load sharing between columns and the central core.  If you know of robust English language articles about this project, I would be very interested in seeing them.

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Christian Parker P.E., M.ASCE
Structural Project Engineer
Princeton NJ
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Original Message:
Sent: 03-20-2023 07:50 AM
From: Olaf Faber
Subject: Mass Timber Moment Frame

Check this out

https://www.skyscrapercentre.com/building/projekt-pi/39979

Greetings

Olaf

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Olaf Faber P.E., M.ASCE
Senior Engineer
Zuerich
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Christian,

I think there are many examples of glulam moment frames already. I know that extensive testing in Europe has been done on them. We have conducted some studies on moment connections with embedded steel plates.

I don't think CLT would be desirable for the frame parts since the two-way action of the cross-layers does not really contribute to frame stiffness. Glulam and LVL are much better choices.

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Daniel Hindman P.E., M.ASCE
Faculty Advisor
Virginia Tech
Blacksburg VA
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Daniel,

You're right, it seems this is much more common than I realized.  I found a thread on eng-tips which had some really great resources and also some unhelpful curmudgeon-y opinions, as is often the case.  I'm seeing connections take a couple different forms, but mostly embedded steel plate with a fastener group in direct shear (similar to the system Andres brought up) or adhesive anchors developing a force couple.  Have you encountered other viable connection options?  Are you aware of any discussion of moment connections in NDS or IBC?

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Christian Parker P.E., M.ASCE
Structural Project Engineer
Princeton NJ
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Original Message:
Sent: 03-20-2023 04:47 PM
From: Daniel Hindman
Subject: Mass Timber Moment Frame

Christian,

I think there are many examples of glulam moment frames already. I know that extensive testing in Europe has been done on them. We have conducted some studies on moment connections with embedded steel plates.

I don't think CLT would be desirable for the frame parts since the two-way action of the cross-layers does not really contribute to frame stiffness. Glulam and LVL are much better choices.

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Daniel Hindman P.E., M.ASCE
Faculty Advisor
Virginia Tech
Blacksburg VA
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Here in Kerala state, a single storey hall for using koothambalam (Malayalam). Two Timber trusses is taken the load of rafters and purlins of roofing including clay tiles. The Timber trusses are placed at the two ends 2metres away from short spans, thereby taking the 4 ridge rafters, at the four corners. The 2 shorter span carries triangular shape portion vertex at the top , longer span trapezoidal. If you are interested I may send the drawing of the wooden trusses wooden ties and struts connected with ms plates and bolts.

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Alex Thomas R.Eng, C.Eng, M.ASCE
Engineer
Engineer Vistar Associates
CochinAlexThomasR.Eng, C.Eng, M.ASCEIndia
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Sketch of the roofing Truss and rafters of one shorter span 

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Alex Thomas R.Eng, C.Eng, M.ASCE
Engineer
Engineer Vistar Associates
CochinAlexThomasR.Eng, C.Eng, M.ASCEIndia
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Original Message:
Sent: 03-27-2023 11:22 AM
From: Alex Thomas
Subject: Mass Timber Moment Frame

Here in Kerala state, a single storey hall for using koothambalam (Malayalam). Two Timber trusses is taken the load of rafters and purlins of roofing including clay tiles. The Timber trusses are placed at the two ends 2metres away from short spans, thereby taking the 4 ridge rafters, at the four corners. The 2 shorter span carries triangular shape portion vertex at the top , longer span trapezoidal. If you are interested I may send the drawing of the wooden trusses wooden ties and struts connected with ms plates and bolts.

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Alex Thomas R.Eng, C.Eng, M.ASCE
Engineer
Engineer Vistar Associates
CochinAlexThomasR.Eng, C.Eng, M.ASCEIndia
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Wooden Truss is placed where the first rafter is starting on the vertex of the first triangle of the truss , longest rafter is at the middle. 

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Alex Thomas R.Eng, C.Eng, M.ASCE
Engineer
Engineer Vistar Associates
CochinAlexThomasR.Eng, C.Eng, M.ASCEIndia
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Thanks for the intriguing example and sketches.  One thing that I am wondering about is what the truss diagonals are doing since the roof load comes through the ridge beams at the high point, rather than at the truss chord points.  Is the truss part of the lateral system? 

You mentioned that the connections are unusual; do you have pictures of the connections?

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Christian Parker P.E., M.ASCE
Structural Project Engineer
Princeton NJ
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Original Message:
Sent: 04-04-2023 09:43 PM
From: Alex Thomas
Subject: Mass Timber Moment Frame

Wooden Truss is placed where the first rafter is starting on the vertex of the first triangle of the truss , longest rafter is at the middle. 

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Alex Thomas R.Eng, C.Eng, M.ASCE
Engineer
Engineer Vistar Associates
CochinAlexThomasR.Eng, C.Eng, M.ASCEIndia
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