session 21 ic2011 niemz

"Cross Laminated Timber (CLT) panels - a new wood based material with high value added"Peter Niemz; ETH Zürich, Institute for Building Materials, Wood Physics, Switzerland

[email protected]; www.ifb.ethz.ch/wood

Portland 6-2011 Peter Niemz (Institute for Building Materials, Wood Physics; [email protected])

Outline

1. Introduction

2. Overview about works from the ETH, IfB/Wood Physics

1. Mechanical Properties2. Sorption, swelling, moisture induced stresses,

warping3. Thermal conductivity, diffusion4. Modeling

3. Examples for using from CLT2


1. Introduction What is cross laminated timber? Wood based material based on solid wood

(boards) Boards or lamellas connected with adhesives,

nails, dowels, key and slots► Elements for the construction (format: 3.4m x

13.7m, up to 0.8m thickness), industrial prefabrication, Schilliger/CH, KLH/ Germany; Binder/Austria and other

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Solid wood wallsNägeli/CH, Thoma/A Soligno/I dowels (Nägeli, Thoma) key and slots nails (Hundegger)

high resistance during earthquake

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Plant for CLT, conected with dowels (Nägeli/CH)

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prefabrication with CNC-machines

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Cross laminated timber, produced from glued cross laminated layers (3-11)start: around 1990 (G. Schickhofer/A, E. Gehri/CH)

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Lamellas in the middle layer glued or not glued together, gaps between lamellas (reduction from stresses)

Grading from surface lamellas (C14-C40), high quality surfaces (optical grading)

Possible loading: tension, compression, bending (beam, disc)

Portland 6-2011 Peter Niemz (Institute for Building Materials, Wood Physics; [email protected]) 8

Bending perpendicular

Board for a road bridge, max. load 40t (Fa. Schilliger Holz/CH)

F


Bending parallel to the surface(higher tension perpendicular)

Roof construction (Fa. Schilliger Holz)

[email protected]

F


costs

additional charge for timber construction(Nägeli/CH):

Timber frame construction: +5% Solid wood wall: +9-10%

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2. Overview about works from the ETH, IfB/Wood Physics

2.1 Mechanical properties

Small samples, medium samples, boards, (scaling effect)

Calculation from mechanical properties (examples: plywood calculation according DIN 68765, FE-modeling, calculation as a laminated material (laminate theory)

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Board thickness: 30 mm; lamella ration: 1 = 10/10/10; 1,75 = 8/14/8; 3 = 6/18/6; small samples (Steiger und Niemz 2004)

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Bending strength = f(board structure)lamella ratio: thickness middle layer/thickness surface layer

In fibre direction

Perpendicular to the fibre


failure by rolling shear (typical for small samples, not for entire board)

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Reduction from bending strength by slots

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bend

ing

stre

ngth

(N/m

m2 )

Without slots with slotsmiddle layer

in fibre dircetion

perpendicular to the fibre


Tests from boards and beams samples(scaling effect)

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PlattenversucheBalkenversuche

a al1

l

F/2 F/2

Test from beams:EN 789 (CEN 1995)

boards

beams


Test from entire boards4 single loads

2.5m x 2.5m x 0.07m), Empa/ETH

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Bending strength from beams and entire boards (Czaderski et al. 2007)

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Producer n min[N/mm2]

meanvalue

[N/mm2]

max[N/mm2]

median[N/mm2]

s[N/mm2]

x05[N/mm2]

beamsA 70 18.7 36.5 50.4 37.6 6.18 25.5

B 78 20.3 39.9 54.4 41.1 6.71 28.0

boardsA 12 35.1 50.7 61.4 50.0 8.20 35.1

B 12 49.6 59.8 68.6 59.5 5.86 48.0

B- better grading from wood


Examples for the calculation from MOE(Czaderski et al. 2007)

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parallel tot he grain perpendicular tot he grain

000, EEm 90090, EEm

plywood analogy (Steck 1988):

33

31

33

0 hhh

Gl. (4)

plywood analogy (Steck 1988):

33

31

90 hh

Gl. (5)

modified plywood analogy (Blass und Görlacher 2003):

33

31

0

9033

0

1

h

hEEh

Gl. (6)

modified plywood analogy (Blass und Görlacher 2003):

33

31

0

9033

0

90

90

1

h

hEEh

EE

Gl. (7)


Conclusions

Influence from fibre direction and board structure (layer ratio)

Using as beams, boards, discs, higher value for tensile strength perpendicular in relation to glue lam

Scaling effect

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2.2 Sorption, swelling, moisture induced stresses, warping

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Sorption

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Lower EMC then solid wood

Internal stresses?Adehesives ?


Swelling and shrinkage

spruce: l = 0.01%/%, r =0.17%/%, t =0.3%/%

CLT:

in plane direction 0.016-0.025%/%

perpendicular: 0.3-0.5%/%

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Portland 6-2011 Peter Niemz (Institute for Building Materials, Wood Physics; [email protected]) April 2011

Vertical profiles of EMC through the samples(Neutron Imaging, Sonderegger et al. 2010), 0%-20/85%

UF 1 C PUR no. of bond lines1

3

5

water73.75d 0.75d


Diffusion resistance factor

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020406080

100120140160180

Variant es

μ [-]

1 10 11 12 13

1 = lamellas glued,10 = not glued ,Distance between lamellas: 11 = 5mm, 12 = 10mm, 13 = 30mm

Dry Cup (20oC)0% - 65% RH.

Influence: µ encreased with no. of

layers Influence from adhesive Board structure (slots,

holes)


Thermal conductivity

Solid wood (spruce): (λspruce≈0,1W/mK)

Parameters: density, EMC, temperature

Solid wood panels (CLT): λCLT< λspruce, solid wood influence from growth rings influence no. of layers influence of holes

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Influence of board structure on thermal conductivity

CLT from spruce: (Bader et al. 2007)

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radial tangential without orientation

ther

mal

con

duct

ivity

(W/m

K)


Thermal conductivity from CLT:influence from the distance between lamellas

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0.080

0.085

0.090

0.095

0.100

0.105

0.110

0

λ [W

/m ּ◌K

]

10 11 12 13

Distance between lamellas in the middle layer: 10 = 0mm, 11 = 5mm, 12 = 10mm, 13 = 30mm


2.3. Moisture induced stresses and swelling pressure

During strong drying cracks in the surface layer are possible

For panels in rooms with low air humidity EMC from around 8% necessary for surface layers

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Cracks in the surface layer during drying (surface layer too wet during production, compression strain needed in surface layer)

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Cracks in the surface layerconditions:production: (20oC/85%), drying (20oC/35%), tensile stresses

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Slots in the surface

without slots

Slots in the middle layer

before gluing:climatization under20oC/35% or20oC/65% not cracks detected(compression stresses)


Modeling of moisture transfer and moisture induced stresses-warping(PhD: Gereke 2009)

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el

Total strain:• elastic: Hooke law• Moisture induced: swelling• Mechano- sorptiv effect

future: viscoelastic+ plastic (PhD Hering 2011)


FE-simulation moisture transfer (Gereke 2009) mit Abaqus


FE-simulation warping (climatic conditions: 20/65%-20/100%, Gereke 2009)

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AR: growth ring angle0-tangential90-radial

LR: Lamella ratio

Pl

De

aa

LR

2


3. Examples for using from CLT

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Prefabricated house (Nägeli /CH)


House produced with solid wood walls (Nägeli AG/CH, used wood: 300m3)

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one family house (Pius Schuler/CH)

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Monte Rosa cottage (Architects ETH)

Foto: Schilliger Foto: Purbond


Bridge, produced with CLT and glue lam (Schilliger Holz/CH)

glue lam

CLT


Schoolhouse (Manchester), prefabricated in Switzerland (Schilliger Holz)


Timber tower (Germany, high: up to 160m)

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Thanks former PhD students Dr. Thomas Gereke, now UBC Vancouver

(modelling warping)

Dr. Walter Sonderegger (ETH)

(thermal conductivity, diffusion)

Dr. Matus Joscak (moisture transfer in wooden walls)

Stefan Hering (modelling stresses in bon lines)

and a lot of other peopels from mi group

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Thanks for your atention

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IfB, wood physics

session 21 ic2011 niemz

Technology

peter niemz institute

building materials

wood wallsngelich

solid wood wall

solid wood boards boards

new wood based material

timber constructionngelich

timber frame construction