[week 19] Strength and durability of Kenaf Stressed Skin Panel extrusion

design

Agricultural fibres can be pressed or extruded to plate material. The design that is elaborated here exists of kenaf particles extruded to a tube.

Kenaf (Hibiscus cannabinus) is a fast growing fiber crop related to cotton, okra, and hibiscus. The plants, which reach heights of 2,4 to 6 meters, are harvested for their stalks from which the fiber is extracted. The fiber is used in the manufacture of industrial textiles, ropes, and twines. Kenaf is among the most widely utilized of the bast fibers. (CES EDUPACk 2009)

Harvesting of Kenaf, source: http://bridgemail.bigbridge.com.au

Panasonic has set up a plant in Malaysia to manufacture kenaf core fibre boards and export them to Japan. Kenaf core fibres are comparable to hard wood. (http://en.wikipedia.org/wiki/Hibiscus_cannabinus)

source: http://www.stramit-int.com/index.html

variables

Input

Fibre type (kenaf core)

holocellulose content (71.24%)

lignin content (23.22%)

ash content (5.93%)

Kenaf core is a product from the flax plant. The properties of resin free fibreboard are superior to wheat straw, reed, palm or meadow (Jianying Xu 2006).

Fibre length (5,5 +- 2,49mm) 1,6//8 cm

Fibre length balances between modulus of elasticity and modulus of rupture.

Fibre diameter (284 +- 136 µm)fiber width (0.82–1.73 mm) cell wall thickness (3.36–5.25 lm) lumen diameter (5.82–10.39 lm)

Resin type (none)

Most fibre boards contain UF or MDI glues. Sometimes the natural lignin in the fibres can provide the necessary bonding.

Resin content (0 %)

Steam-injection during pressure -> yes

Steam injection gives better properties to the board (widyorini2005)

Pressure (0,6 MPa) 0,6/0,8

This results in a density (500 kg/m³). 300

Time of cooking (10min) 20/30

Cooking of fibres before bonding gives higher internal bonding and less thickness swelling.

Test conditions

Relative humidity (10-90%)

Outcomes

Modulus of Elasticity MOE (2,3 ± 0,1 MPa)

Modulus of Rupture MOR (19.4 ± 2,0 MPa)

Internal Bond IB (0,24 ± 0,04 MPa)

Thickness Swelling TS (18 ± 1 %)

design strength performance

height 350 mm

width 1200 mm

flange thickness 28 mm

web thickness 28 mm

Elastic deformation

MOE of 2,3 MPa results in a vertical deformation of the roof of 5/384*1,7*9000^4/ (2400*2*28*1200*175^2)= 29 mm. This is within the tolerance of 45 mm.

Long term deformation

Long term deformation caused by creep is not investigated yet. MDF shows a a comparable creep behaviour that could be studied. Conclusions from this study (Fernandez1998) are that the stress should remain below 20% of MOR to avoid rupture. Also a high relative humidity should be avoided.

Stressed Skin Panel tests with wood webs and OSB flanges showed that tests on deformation and Modulus of Elasticity showed similar outcomes (Kliger 1995).

bending strength

With a MOR of 17,4 MPa and a bending resistance of 2,1 *10^9 mm⁴ is a bending moment of 204 kNm possible. The designed load of 21 kNm is below this.

compression strength

The roof leans on the walls. The weight per half roof element is 70*4,5*1,2=380 kg. The surface of a wall column is 2 sides*260 depth*28 thickness=. This means that the compression force is 380*9,81/14560=0,26 N/mm². This is below the maximum compression force of 17,4 N/mm².

design moisture performance

Moisture and temperature conditions are calculated for worse case scenario.

inside temperature 20 ^oC

inside relative humidity 60%

outside temperature -10 ^oC

outside relative humidity 50%

To control relative humidity during high outside relative humidity, a vapour barrier around the construction could be helpful. Food industry uses bee wax coatings to improve the freshness duration.

The same wax layer on the inside and outside will trap the moisture with condensation as result.

A solution is to apply a thicker wax layer on the inside to lower the vapour pressure in the construction and insulation.

Rtot=0,04+0,06+0,06+5,00+0,06+0,10+0,13=5,45 m²K/W

Q=30/5,45=5,4 W/ m²

Tis= 20-0,13*5,5=19,3 ^oC -> Pio.max=2240 Ps

Tloam= 20-(0,13+0,1)*5,5=18,7 ^oC -> Ploam.max=2175 Ps

Twax= 20-(0,13+0,1+0)*5,5=18,7 ^oC -> Pwax.max=2175 Ps

Tflange= 20-(0,13+0,1+0,06)*5,5=18,4 ^oC -> Pweb.max=2117 Ps

Tstraw= 20-(0,13+0,1+0,06+5)*5,5= -9,1 ^oC -> Pweb.max=281 Ps

Tupperflange= -10+(0,04+0,06+0)*5,5= -9,5 ^oC -> Pweb.max=271 Ps

Tes= -10+0,04*5,5= -9,8 ^oC -> Pweb.max=264 Ps

Figure, Glazer diagram of vapour pressure in construction.

references

Jianying Xu. Development of binderless fiberboard from kenaf core, Journal of Wood Science, springer: Japan, 2006.

Kliger, IR, Pellicane, PJ. Prediction of Creep Properties of Chipboard Used in Stressed-Skin Panels Research scientist, Journal of Testing and Evaluation
Volume 23, Issue 6 , Chalmers University of Technology, 1995.

Ragil Widyorini, Jianying Xu, Takashi Watanabe and Shuichi Kawai. Chemical changes in steam-pressed kenaf core binderless particleboard, Journal of Wood Science. Springer: Japan 2005.

[week 18] extruded kenaf design

An animation of the stressed skin panel design:

[week 15] final drawings

download drawings

[week 14] alternatives and conclusions

Every system design has some alternatives that I will show below. There can be made conclusions about the system, pavilion design and Cradle to Cradle.

system design 1: technical

alternatives

1 The roof cladding can be coated steel, aluminium, copper, zinc, or bitumen.

2 Insulation can be EPS, glass wool, or stone wool.

3 substructure can be steel or aluminium

4 structure can be steel or aluminium

5 interior cladding can be stone wool, perforated steel, bio-rock or gypsum board

choice

1 aluminium for its resistance to release toxic metals in the rain water.

2 glass wool for its low mass and environmental aspects

3 steel for its lower costs and environmental aspects

4 steel for its lower costs and environmental aspects

5 gypsum board for its costs

further research

The following topics can still be further elaborated:

• coatings that do not pollute underlying metals
  

  system design 2: steel-wood
  

alternatives

1 The roof cladding can be wood tiles, coated steel, aluminium, copper, zinc, or bitumen.

2 Insulation can be flax wool, sheep wool, cork, EPS, glass wool, or stone wool (cellulose contains borax).

3 substructure can be fibre board, steel or aluminium

4 structure can be steel or aluminium

5 interior cladding can be wood, stone wool, perforated steel, bio-rock or gypsum board

choice

1 wood tiles for its low environmental aspects

2 flax wool for its low costs and environmental aspects

3 fibre board for its low costs and environmental aspects

4 steel

5 gypsum board for its costs

further research

The following topics can still be further elaborated:

• connection of wood shingles without steel nails
  

• • system design 3: straw board – glue
    

alternatives

1 The roof cladding can be wood tiles.

2 Insulation can be flax wool, sheep wool, cork, straw, or bio-EPS.

3 webs can be straw board or wood

4 flanges can be straw board or wood

5 interior cladding can be wood or gypsum board

choice

1 Wood tiles for its low environmental aspects.

2 Straw for its local availability and applying the heat resistance.

3 Straw board for the thickness and absence of glues.

4 Straw board for integration of functions and better flow of insulation.

5 Wood for its good environmental aspects.

further research

The following topics can still be further elaborated:

• market and feasibility investigation
  
• FJI joists with natural glues
  
• FJI joists with cold wood connections
  
• moisture and long term effects
  

  system design 4: wood joints
  

alternatives

1 The roof cladding can be wood tiles or EPDM

2 Insulation can be flax wool, sheep wool, cork, or bio-EPS.

3 structure can be wood

choice

1 EPDM for its low environmental aspects

2 flax wool for its low costs and environmental aspects

3 wood

further research

The following topics can still be further elaborated:

• wood squire splice joints system design
  

  system design 5: solid wood
  

alternatives

1 The roof cladding can be wood tiles or EPDM

2 Insulation can be flax wool, sheep wool, cork, or bio-EPS.

3 structure can be wood

choice

1 EPDM membrane for its low environmental aspects

2 flax wool for its low costs and environmental aspects

3 wood

further research

The following topics can still be further elaborated:

• overlapping short solid wood parts for Q-concept floors
  

pavilion design

The system design 4 with only wood and other natural materials does fit the criteria very well. Making the wood joints in an industrial way is also innovative.

further research

The following topics can still be further elaborated:

• climate, water distribution and building services
  
• finishing's with waste material
  
• construction of the attached glass house
  

  Cradle to Cradle materializing
  

  why
  

Savings during the exploitation of a building can be easily defended during the design phase. More difficult are savings at the end of the life span because of higher component or scrap value. But with rising prices of raw materials and awareness of the environment some attention for the Cradle to Cradle ideas worth it. Improvement of human health conditions is of importance for the user of the building. With only a small decrease of absenteeism is a large cost saving possible.

evaluation

Using materials like before the first industrial revolution will mean a more effective use of the materials. This is not always possible today. And today's designs require forms that cannot be made from only natural materials. The only way out to materialize this design is to use technical materials like recyclable watertight foil.

Does this mean that this experiment has failed because 100% Cradle to Cradle is not achieved? In my opinion not because it shows that innovation can reach the destination at the end. This may be done in little steps but is must happen if we want to give our children the same opportunities that we have.

SWOT

strengths

• willingness of parties
  
• better performance than practice as usual
  

weaknesses

• not objective without quantitative comparison
  
• commercial background of certification
  

opportunities

• future benefit
  
• simplification of details with less cost
  

threats

• building regulations
  
• extra costs
  

  further research
  

This research is not complete and raises more questions than answers. Further research could go in to the following topics:

• 
  

[week 12] building the prototype

System designs 3 and 4 will be mechanical tested because of some adjusments from existing roof systems.

system design 3
It will be made of straw board attached to the soft wood flanges with natural glue.


Figure 12.1, axonometry of system design 3

For a specimen scale 1:2 (35x180x4500 mm) will be needed:
- straw board 6x200x4500 mm
- soft wood 2x 2335x4500 mm
- glue 2x 4.5x25 grams



Figure 12.2, preperation for a scale model 1:2 of system design 3

system design 4
It will be made from only wood and other natural materials.

Figure 12.3, section of system design 4

For a specimen scale 1:1 (75x275x2000 mm) will be needed:
- soft wood 3x 75x275x1200 mm
- soft wood sub beams 50x50x1000 mm


Figure 12.4, testing a scale model 1:5 of system design 4

[week 11] LCA comparison

Now the system design options are determined they can be compared with a Life Cycle Assessment.

1. steel

	weight		E costs
Steel coated, corrugated	8.60	kg/FE	0.02	(eur/year)
glass wool 150	7.50	kg/FE	0.01	(eur/year)
VAPOUR BARRIER	1.00	kg/FE	0.00	(eur/year)
corrugated steel filling	10.92	kg/FE	0.12	(eur/year)
Steel beam Hea 260	8.35	kg/FE	0.10	(eur/year)
gypsum board 12mm	1.56	kg/FE	0.02	(eur/year)
total	37.93	kg/FE	0.28	(eur/year)

Figure 1, life cycle and sub cycles of steel beams.
1.1 life time

The durable materials will make a longer life of components possible. A technical life of 105 years is realistic with components that last three building uses. The total environmental effects will be divided over this technical life for the effects per year.

1.2 construction strength

If the bay distance is two meter, than 260 mm high beams are sufficient.

1.3 thermal insulation

The 150 mm glass wool results in an Rc value of 4. 1 m2K/W.

2. steel-wood

Wood shingles 2x 9 mm	8.64	kg/FE	0.01	(eur/year)
plate straw 18	8.1	kg/FE	0.01	(eur/year)
glasswool 280	14.00	kg/FE	0.02	(eur/year)
VAPOUR BARRIER	1.00	kg/FE	0.00	(eur/year)
plate corrugated	9.00	kg/FE	0.18	(eur/year)
steel C360/100/38 x 2,5mm	12.21	kg/FE	0.14	(eur/year)
			0.00	(eur/year)
total	52.947	kg/FE	0.35	(eur/year)

2.1 life time

disassembling possible for reuse: yes

lifetime: 2 building uses = 70 years

Only the wood shingles should be replaced after one building use.

2.2 construction strength

The steel C profiles are spanning the building every meter.

thickness	2.5 mm
dimensions	C360/100/38 mm
dead+live load	1.5 kN/m2
bending moment	15.2 kNm	< mmax =" 24">

2.3 thermal insulation

The FlexFrame system can fit the criteria if the insulation is thick enough. Because the steel profiles form linear cold bridges of 2.5 mm every meter the thickness of insulation has to be double of the thickness without the cold bridges. Together with 18 mm straw board and wood shingles on top there will be a heat resistance of 4.1 m²K/W.

3 laminated beams

An m² of roof consists of

EPDM-membrane 1.14 mm	1.41	kg/FE	0.05	(eur/year)
plate straw 18	8.64	kg/FE	0.01	(eur/year)
flax wool 140	7.00	kg/FE	0.02	(eur/year)
FJI joists	4.93	kg/FE	0.03	(eur/year)
Vapour barrier	1.00	kg/FE	0.00	(eur/year)
batters 38x50 /1,2m	0.7125	kg/FE	0.00	(eur/year)
gypsum	1.56	kg/FE	0.06	(eur/year)
	25.25	kg/FE	0.17	(eur/year)

3.1 life time

Technically these materials could be reused after 35 years. But this would need more labour than new materials. That is why only one building use is prognosed.

3.2 construction strength

If the bay distance is 0.3 m, than 380 mm high FJI-beams are sufficient.

3.3 thermal insulation

The FJI-beams are negligible as cold bridge. The space in between can be used to place 140 mm flax wool insulation that results in an Rc value of 4. 0 m²K/W.

3 wood joints

4 solid wood

[week 10] final design

Elements of the structure:

Bay of the structure: