The Joint - The Circular Joint

The Circular Joint

Assignment 3 - The Joint The Circular Joint Joachim Daetz, Anastasiya Volkova, Yuxin Wu WoodProgram - November 2021

Assignment................................................................................................... 07 Analysis....................................................................................................... 09 Mortise&Tenon Joint.................................................................................... 15 Research Applications for a Tripod Joint................................................................. 17 Nature as a Rolemodel............................................................................ 19 Nur Holz................................................................................................ 21 Holz100................................................................................................. 23 Focus And Rules.......................................................................................... 25 BrainStorm Ideas.......................................................................................... 27 Decided Design. ........................................................................................... 29 Studies/Tryouts NailGun................................................................................................. 31 Glueless CLT........................................................................................... 35 Round Tenon&Mortise........................................................................ 37 Introduction of Rope............................................................................... 39

Content

Final Design................................................................................................. 41 Hydrolic Pressure Test. ................................................................................. 47 Hydrolic Pressure Test - Analysis................................................................... 51

Source: WoodProgram

7

Assignment

Your next workshop excercise is to design and manufacture a wooden joint that meets a few simple criteria: it is made primarily of wooden components it is simple, effective and easy to manufacture it is as strong as possible it is architecturally appealing The primary material for the joint is sawn spruce found in our workshop.

The material can be sawn, planed, bent, split, glued and crafted as you see appropriate. You may use other materials (hardwoods, steel, rope, etc.) to complete the joint as needed but remember that wood must be the primary material.

Analysis: To begin the project each student should to find an interesting example of a wooden joint used in building sca/e and present those as a group. Use your own drawings and diagrams to descibe it. Explain how the joint works in the building stucture.

The visual and structural properties of the chosen joint should be analyzed and presented on Tuesday 12. 1 0 General instructions: The joint is to be designed and manufactured in groups of 3 or 4 persons. As before, make quality drawings, both to communicate your design and to help you in the workshop. Work with models and mock-ups.

The production drawings of the final joint should be finished by Thursday 21. 10. lf you‘re not sure how to execute your intentions, ask for advice.

Once you are sure, test your design and make it better.

Join: 1.

2.

3.

4.

5.

6.

7.

To put/bring together so as to make continuous or form a unit To put or bring into close association or relationship To connect (points), as with a straight line.

To meet and merge with To become a part or member of To come into the company of To engage in; enter into

Source: WoodProgram

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9

Analysis

What is a joint?

A joint is a woodworking technique that is used to create more complex structures, as one piece of wood has its limits. So a joint is mainly used to combine wood pieces to create a bigger whole, like a frame that will then further help create a building.

What characteristics does a joint need?

Strength, flexibility, toughness, appearance. Which depend on the material used and the purpose it is used for.

What is important to remember?

Humidity expands and contracts the timber - this needs to be respected and accounted for in the design. Meaning: Keeping some air space for example.

10

Wood Connection kinds

longitudinal connections

corner connections

diagonal connections

cross connections

11

Connection methods

tying together

crossing over

interlocking

over-/underlaying

12

Source: Hansemann; Puklavec; Vidacak-Zimmermannsmäßige Verbindungen aus Holz

13

What aids are used to connect two pieces of wood?

The knots/joints advanced with its time, and became more and more advanced as technology grew.

For wooden connections the following aids are used: Strings/fasteners, dowel-types, cones, offsets, notches, holes, tongues, comb-connections, With external help like steel: bolts, timber-rivits, screws, shear connectors and proprietary connections can enrichen and strengthen the final result - compared to just using wood on wood.

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Gra in D ire ctio n

Gra

in D

irec

tion

Grain Direction Rail

Shoulder Mortise

Stile Wooden Nail

Tenon

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Mortise and tenon joint

One of the oldest joints found near Leipzig (Germany) around 7000 years ago. This joint is seen as one of the strongest joints, along the dovetail joint. It can be either glued together or locked in place by wooden nails/wedges.

The tenon shouldn‘t be bigger than 1/3 of the size of the timber in which the mortise is carved in.

16

Sibelius Hall in Lahti (source: puuinfo.fi)

Ghent house extension by Atelier Vens Vanbelle (source: dezeen.com)

koichi takada architects - east village urban marketplace in sydney (designboom.com)

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Applications for a tripod joint

Sibelius Hall The load-bearing structure in the Forest Hall consists of a large-scale frame resting on nine wooden columns. Reminiscent of the branches of a tree, this 3D structure made of glue-laminated timber supports the wooden roof sections. The massive glue-laminated pylon from turned spruce supports a frame measuring 11.2 x11.2 m. The members in the space structure are interlinked by dowel joints. The actual load-bearing structure in the hall consists of massive glue-laminated frames that support the roof and glue-laminated trusses on which the ceiling structures rest.

Ghent House Wooden fins radiate out from the top of each column, creating a geometric pattern of struts that support the roof. Glass inserts in the ceiling direct views to the sky, while a glazed wall directs views out into the garden.

Marketplace in Sydney The design draws its influence from the forest and landscape- in ways that is illustrated through the use of timber as the main component, and texture to focus on the tree-like columns that grown and fan-out to merge with the ceiling.

Timber profiles create the textured tree trunks and conceal the structural columns.

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Source: Kaerkkaeinen 2003

Source: https://mywisconsinwoods.org/

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Nature as a rolemodel

Cell Wall Structure Different layers = different angles which help prevent cracking and making it more elastical etc... maybe this can be imitated with 5 different boards with 5 different grain directions?

Strong Versus Weak Branches U-shaped branches are stronger. Here’s why. The union where two branches (or a branch and the main tree trunk) come together ideally allows for the growth of specialized wood under the branch bark ridge.

The branch bark ridge wood limits the movement of disease and water from one branch to the other, should one of the branches become diseased or wounded.

The V-shaped branches (B in the image) provide little space for branch bark ridge growth, increasing the chance for decay. The bark ridge that does develop is soon over-grown by the branch wood, making for a very weak union.

https://mywisconsinwoods.org/2014/02/04/strong-vs-weak-branches-know-the-difference/

Whole Trees Structures - National Gateway This mixed use building sits on the Potomac River in Arlington, VA and features over 1,500 new residential units, 625 hotel rooms, over 2 million square feet of office space, and nearly 250,000 square feet of retail, including a grocery store. A focus on open, public spaces including parks was a large part of this project and WholeTrees was asked to provide 14 branching, sculptural biophilic tree columns and 10 milled timber benches for the open air courtyard at the building’s main entrance. Working closely with architects, landscape architects and engineers, these White Oak trees were carefully selected with the use of 3D scanning technology. These scans were then converted into Revit files and sent to the Architects for precise rotation and location points resulting in a seamless installation and gratifying naturescape. We’re proud of the collaboration and excited to see these cull trees get new life and appreciation for years to come.

https://wholetrees.com/

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NurHolz

Trees are withstanding wind, weather and even storms. This is why timer is the perfect material for construction. It is lightweight, flexible, highly durable, has outstanding qualities regarding insulation and a high fire resistance as well as a low conductivity for heat and cold. NURHOLZ walls are self-supporting and a lot more stable than other timber construcons without glue, due to their unique bolting. Because of the interlocking screwed connection not only the core layers are bearing the weight of the constrcution, but also the connected vertical board layers are supporting it. The board layers that are arranged crosswise and diagonal are additionally making the NUR-HOLZ panels torsion-resistant - but they still stay flexible enough to provide maximal earthquake protection.

NUR-HOLZ is offering internal and external walls with a thickness ranging between 12.5cm to 35cm, as well as ceiling and roof panels between 17,9c, and 20,8cm and a span of up to 6m. The cheiling panel is also often used as a floor. The specifically for the NUR-HOLZ panels designed connections for walls and ceiling are providing an airproof cover for the solid timber shell and ensure an easy and safe construction. All needed connections are automatically calculated according to your planning.

The solid NUR-HOLZpanels are serving as an energy storage, reducing the energy expenses op to half compared to conventional construction methods. Solid timber is the ideal building material for decades, even centuries. At the end of utilization phase, meaning after deconstruction, the material turns into a new resource through composting.

Source: https://www.nur-holz.com/

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Source: Thoma.at

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Holz100

Holz100 (“holz” = wood in German) is a cross-laminated, prefabricated 100% pure solid wood building system connected by wooden dowels – it is the product of our founder Dr. Thoma’s aim “to build the healthiest house in the world – with the highest standards of build”. Holz100 is therefore the ultimate all-in-one solution for health, safety, sustainability, and wellbeing for both people and the environment. It is certified by both FSC and PEFC, our wood is harvested at the ideal time (‘moonwood’ or lunar harvested) in high altitudes, selectively hand-picked and air-dried for the highest quality achievable for timber products.

These methods collectively ensure that even without a trace of preservatives, glue, toxins, chemicals, or VOCs, our building system ensures extraordinary longevity and quality that results in no air leakage, shrinkage or thermal bridges.

Contrary to the great misconception that wood cannot be fireproof, heavy timber construction has an inherent level of fire resistance which increases with thickness as the outer layer chars and becomes a protective insulation layer that slows down the burning rate. The strength and load carrying capacity is not as compromised as steel which buckles under extreme heat due to its significantly higher thermal conductivity and allowing heat to spread rapidly, causing beams and floors to collapse.

In addition to vertical loads, buildings are also exposed to horizontal forces. Horizontal loads can be caused by wind, earthquakes and other impcat loads, Due to the typical processing of the board layers of a Holz100 wall in 3 different directions (horizontal - vertical - diagonal), Holz100 walls can also absorb and dissipate such forces. The required wall thickness or the required combination of 3 board layers is calculated from the characteristic, holizontal load.

Source: https://www.holz100canada.com/

Mortise Piece

Tenor Piece

„Leg“ creation

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Focus and Rules

There are 3 parts to focus on in this exercise: - Creating a Leg without glue (NurHolz or Holz100) - Strong Mortise - Strong Tenor piece What do we set ourself as rules for this design process?

- Disassemblable - No Glue - No Steal - Strong - Easy to produce - Aestetic Questions that need to be focused on: - How to prevent the legs from spreading?

- Grain directions?

- Strength over sustainability?

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Source: W.W. Robbins and T.E. Weier

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Brainstorm Idea

Finding a tree with 3 similar sized branches Fell it Dry it Cut into slizes so that the branch is still attached but the rest is cut off Attach together Cut Branches at approximatley same length.

Reason: Branches grow from the center of the tree - thus they must have a natural strong connection. As the grain grows from inside to outside.

Have to skip it: Not enough time and no own trees to fell.

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70 13 13 20 13 13

5

1 42

0 30

70

81

° 30.00

8 8 8 20 8 8 8

17 46 17

40

7 LAYERS

0 26

80

2 25

SECTION 1:5

3 20

25

70

PLAN 1:5

3

ELEVATION 1:5

ASSIGNMENT 2: THE JOINT

1

29

Decided Design

Making the center mortise peace round - learning from nature as logs/ trunks are also round. Maybe it also maximizes the surface area the tenont has on the mortise. Strengthend by a natural rope around the base.

70 13 13 20 13 13

17 46 17

70

30.00°

8 8 8 20 8 8 8

81

Deviding the legs of the joint into 7 layers. Based on the idea of microscopic pictures of cell wall structures. As421 one00 cell has 5 different 3 “grain” directions to be as stable/flexible as possible at the40same time.

Tenon&Mortise joint connection.

5

7 LAYERS

0 26

80

25

3 20

70

PLAN

ELEVATION 1:5

JOACHIM, YUXIN, ANASTASIYA

3

ASSIGNMENT 2: THE JOINT

1:5

PROTOTYPE

1

25

SECTION 2 1:5 Pegs/Wooden Nails as a substitution of glue. Screws would have been better in terms of disassembly, but in our case we had to make shift with what we had in our workshop and the wood screw making tools where too big for our scale.

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Test 1

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Studies/Tryouts Nails Gun

Wooden Nails

Blow Up of the pieces, due to sheer pressure.

Solution: Predrilling wholes and clamping the boards to the desk.

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Nails Gun Test 2

Clamping of boards & Predrilling

4 Layers with 3 different grain directions. Idea from cell wall strucutres but also from NURHolz or Holz100 constructions.

First and last are parallel; the second is agled at 60°; and the thrid is perpendicular.

Test with close on the edge nails

Obvious Fail with close edge nails

The cracks only occured in the boards that where either parralel or perpendicular. The layer (second from the left) that is angled at around 60° did not crack!

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Note: These are the available board sizes in the workshop. If we take the board No.2 - 92mmx20mm - we will have the least waste from cuttage. As sustainabilty is our main goal not only the cost of production but also the waste that is produced in the process should be aimed at. Thus, with this board we could make many more usable planks out of our 70mmx8,3mm sizes.

As we can cut the plank in half (hight wise) which will reduce the working time at the joiner by alot but also saves many m³ of material.

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Jig

Depth of wooden Nails

Layers of final Legs (6 legs in 1 board) = Less cuttage. Little gap is the width of the table saw blade

Final legs before and after sanding

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Glueless CLT

To create our own glueless “Cross-Laminated Timber” (CLT) we made a jig part, which will ensure that our boards stay in place when we nail them with the wooden nailgun. Further more it helps to create new legs for our joint in quicker time.

It consists of 7 layers: Layer 1: One Board Layer 2: Seven Boards - perpendicular to the first layer Layer 3: Nine Boards - angled at 60° to the first layer Layer 4: Tickest Board with a dowel at one side Layer 5: Nine Boards - angled at 120° to the first layer Layer 6: Seven Boards - perpendicular to the first layer Layer 7: One Board The challenges we face with our decision to make our own glueless CLT were amongs follows: - As we chose to only have one board width it took us 9 boards to cross our total length. Which lead to small pieces on each end of the board that cant be fixed with a nail as it would just split them in half - The different directions of the boards and the 7 layers made it complex to nail together. Ensuring to have at least 2 nails in each board to prevent movement whilst under pressure.

- The pressure of the compressor is not always consistent. So finding the right pressure to ensure that the nails go all the way through all boards but not too far in - was difficult. If a wooden nail didnt go all the way in the pressure from the nailgun blew up the rest (around 1mm) of the nail that stuck out at the top.

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Round Tenon&Mortise

For our round tenon&mortise joint we had a short phase of worry, as the CNC in our workshop was not able to provide us with the demands we wanted it to have. Cutting the tenon in a round shape while keeping the part of the tenon untouched that would later then be fitted into the mortise. So we had to change our perceiption of this joint and with the help of Hector (who had structural engeneering experience prior to this course) found out that this part is not really under alot of pressure IF we introduce a rope that would keep the legs together. So it could just be a dowel or a peg that would keep the leg in place at the tenon&mortise connection.

Luckly, the round sanding mashine in our workshop had, more or less, the exact right dimensions that we needed for our joint. The challenge was to find the mid point in order for the legs to all have the same central sanding. But with the help of a, yet another yig, we succeeded after failing at our test pieces.

The mortise piece was then chiseld down to have the dimensions the round sanding mashine provided for us (around 80mm). We tried to take a grain direction for the mid piece that would allow least crackige (radial).

Once we had both pieces fit PERFECTLY (slight exaggeration as our handcrafts are rather underdeveloped :D) we needed to drill holes into both parts to fit our own dowels into it. For this we needed again jigs that would keep the pieces fixed to the right point, in order to prevent the pieces from moving around once the pressure of the drilling mashine came down.

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LOAD

2

ELEVATION 1:5

70

20

8 1/3

12 0.0 0°

80

7 LAYERS

20

40 30.00°

WOODEN NAILS

ROPE / CABLE

1

PLAN 1:5

3

SECTION 1:5

ASSIGNMENT 2: THE JOINT

20

80

92

21

8 27

34 5

9 39

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Introduction of Rope

As the load is being placed on top of the joint, the force will travel through the legs into the ground. Naturally, the legs will start spreading from the load, putting pressure on the tenon&mortise joint.

There are many ways to prevent the legs from spreading, e.g. stronger joint connection or introducing a rope.

We chose the rope as it is a durable element.

The rope will try and keep the legs in place in order for our “relativly weak” connection to survive as long as possible.

Load LOAD

2

ELEVATION 1:5

Through or Around?

Splicing Rope?

Truckers Hitch Knot

70

80

YERS

20

21

8 27

ROPE / CABLE

3

SECTION 1:5

JOACHIM, YUXIN, ANASTASIYA

Or one bigger one?

ASSIGNMENT 2: THE JOINT

30.00°

Two Holes?

WOODEN NAILS

ECO-JOINT PROTOTYPE

20

40

9 39

92

20

8 1/3

Natural Rope

Less crackige in one?

Self Tightening Knot

1 PLAN

1:2 JOACHIM, YUXIN, ANASTASIYA

CIRCULAR JOINT

ASSIGNMENT 2: THE JOINT

80 70

20

8 1/3

40

1

12 0.0 0°

7 LAYERS

41

Final Deisgn

It was a long way to this point, even though it was only a talk over 3 weeks but due to our many studies, fails and lesson-learned we arrived at a result that we could be proud of. We stayed true to our rules/concept that we set out for our selves. Maybe the point of “easy production” wasn’t exactly matched - yet, now that we have all the jigs, I am sure the next joint will/could be build alot faster.

Componants of the final design: - 3 Legs (glueless CLT) with round tennon connection (added dowels) - 1 Round mortise with 3 holes to fit the dowels - 3 Ropes connected to the center piece of our own CLT, finalized with a simple knot, which in our case would self thighten under the added pressure. Going through a drilled slot of 2x10mm wide holes next to each other and then inter locking each other below the middle of the mortise piece.

- 1 round stick extending from the middle of the mortise piece to ensure the ropes are meeting in the middle We are happy to have made a joint that, in our eyes, is circular in many ways. Circular in the sense of the tenon&mortise, in the sense of being able to disassemble the whole thing and in the sense of reusing or upcycling it. If we want to go a level deeper we could also say that the wooden nails were circular (looking like knots in a tree) and the rope of course also being round. Maybe next time we also make the legs round? ;) We are excited for the testing part - to compare how this method would scale with more modern techniques used in other groups (meaning steel, glue, CNC etc.). We try to stay realistic and keep our expectations not too high, as we also know that better handcraft skills could have made the joint stronger.

YET, by all means, we are the group that had the most fun in the process - laughing, giggling and just having fun trying out random things to see if they work or not. Mainly they didn’t but at least now we know. In some cases we even felt like we distrubed the other groups around us working with our laughter.

2 1:2 ASSIGNMENT 2: THE JOINT

ELEVATION

JOACHIM, YUXIN, ANASTASIYA

CIRCULAR JOINT

42

2

LOAD

SECTION

1:2 12 SISAL ROPE

ASSIGNMENT 2: THE JOINT JOACHIM, YUXIN, ANASTASIYA

° 30.00

70

3 92

30

CIRCULAR JOINT

20

12

43

60

0 30

30

WOODEN DOWEL

WOODEN NAILS

44

45

46

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Hydrolic Pressure Test

The test was held at the civil engineering lab at the Aalto Campus.To ensure fair testing conditions for all the joints we weigh the joints to have a weight to pressure ratio. The weight of our joint was 2,39kg and thus the second lightest one out of the four groups.

We centered the joint underneath the hydrolic pressure mashine. And placed the legs on 3 pieces of wood to create more distance to the floor as we had the central dowel that could touch the ground and falsefy the result of the test as the pressure would just go through that and not the legs. The 2 upper pieces of wood were covered in industrial oil to create friction and allow the legs of the joint to slide outwards.

Then the engineers began to apply pressure gradually. Every now and then shouting out: “2 kilo - 3 kilo - 4 kilo...” And thought: OH GOD it only holds up 4 kilos and is already starting to crack. But soon I realized that he meant kilo newton and 1 kN converts to roughly 100kg of pressure.

Some relief was had.

The interesting part of our joint was that it was rather flexible. It was not our intention but the leg to mortise ratio was almost 180° towards the end of the test. Meaning that it was almost flat and parallel to the ground.

One can imagine that the dowel we used was not getting happier the more it was forced into a 60° angle.

We actaully had to go through 2 tests as the first time we didn’t stack the joint up high enough so the middle dowel supposedly touched the ground. In our first run our joint could withstand 7,3 kN and in our second test 6,4 kN. As there were already hearable cracking going on in the first test its difficult to say for sure if our joint might could have withstood more than 6,4kN but either way our team was happy that it didn’t already fail at 10kg of pressure as we were too afarid to even stand on the joint prior to the test. The self confidence was high :) To give a reference of how the other joints did: 2,73kg = 5,85kN | 2,06kg = 7,6kN | 2,92kg = 10,53kN Pokerface Quinn was sitting in the background in all our videos not even flinshing as the joint cracked. Worth a watch.

48

49

50

a

b

c

d

e

f

g

h

51

Hydrolic Pressure Test - Analysis

Although our joint cracked “only” at one dowel, there are many other signs that the joint was experiencing severe pressure during the test.

Which leads us to think - how much longer would the joint would have hold up even if the dowel stayed in tact for a while longer?

The other signs are not as visible as the obvious crack at the dowel, but once we looked at the pieces closer one could see: a,b&c) That no other dowel or technique for a tennon and mortise connection would have hold up under the angle that our joint was forced into towards the end of the test. The legs were almost flat and up tot the same level as the mortise piece (180°. The sheer angel of the dowel to the legs became too steep and the wooden dowel cracked. A stronger dovetail connection might have already broke earlier? d,e&f) That the rope carved deep into the spruce we used and even began to create a crack long the grain direction moving upwards towards the middle of the mortise. Further more the rope started to rip as well (e) - either due to the pressure or it got stuck at a piece of wood and due to the friction began to tear apart. g&h) To be honest in picture g we already made the mistake of not trusting our guts and decided to nail some more wooden nails into the leg just before the test, as we thought it would make it stronger. Which lead to servere cracks even before the joint was put under pressure.

We decided to go angainst our gut and go with logic - big mistake. But luckly the cracks that we created were in placed where there wasn’t that much pressure applied. The cracks that we marked with red arrows are the ones that acctaully occured during the test and are a result of the pressure applied. Eventhough this grain direction is the strongest one it still cracked. How deep we dont know, but it will leave the question how long until the cracks would have given in to the pressure?

Assignment 3 - The Joint The Circular Joint Joachim Daetz, Anastasiya Volkova, Yuxin Wu WoodProgram - November 2021