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

niemzp@ethz.ch; www.ifb.ethz.ch/wood

Outline
1. Introduction
2. Overview about works from the ETH, IfB/Wood
Physics
1. Mechanical Properties
2. Sorption, swelling, moisture induced stresses,
warping
3. Thermal conductivity, diffusion
4. Modeling
3. Examples for using from CLT
Portland 6-2011 Peter Niemz (Institute for Building Materials, Wood Physics; niemzp@ethz.ch) 2

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


Solid wood walls
Nägeli/CH, Thoma/A Soligno/I
dowels (Nägeli, Thoma) key and slots
nails (Hundegger)
high resistance during earthquake


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


prefabrication with CNC-machines


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

 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)


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

Bending
perpendicular
F


Roof construction (Fa. Schilliger Holz)

Bending parallel to
the surface
(higher tension
perpendicular) F

info@schilliger.ch


costs

 additional charge for timber construction
(Nägeli/CH):
 Timber frame construction: +5%
 Solid wood wall: +9-10%


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)


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

In fibre direction

Perpendicular to the fibre

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)


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


Reduction from bending strength by slots
bending strength (N/mm2)

in fibre dircetion

perpendicular to the fibre

Without slots with slots
middle layer

Tests from boards and beams samples
(scaling effect)

boards

su ch e
Ba
lke en ver Test from beams:
t
nve beams P lat EN 789 (CEN 1995)
rsu a l1 a
che F/2 F/2

l


Test from entire boards
4 single loads
2.5m x 2.5m x 0.07m), Empa/ETH


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

Producer n min mean max median s x05
[N/mm2] value [N/mm2] [N/mm2] [N/mm2] [N/mm2]
[N/mm2]
beams
A 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
boards
A 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)
parallel tot he grain perpendicular tot he grain

Em ,0  E0   0 E m ,90  E0   90

plywood analogy (Steck 1988): plywood analogy (Steck 1988):
h h
3 3 3
h
0  3 3 1 Gl. (4)  90  13 Gl. (5)
h3 h3

modified plywood analogy modified plywood analogy (Blass
(Blass und Görlacher 2003): und Görlacher 2003):
 E  3 E90 3  E  3
h3  1  90 h1 h3  1  90 h1
3
 E0   E0 
0    Gl. (6)  90 
E0   Gl. (7)
3 3
h3 h3


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


2.2 Sorption, swelling, moisture induced
stresses, warping


Sorption

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%/%


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

UF 1 C PUR no. of bond
73.75d 0.75d

water lines
1

3

5

Portland 6-2011 Peter Niemz (Institute for Building Materials, Wood Physics; niemzp@ethz.ch)
April 2011

Diffusion resistance factor
180 Dry Cup (20oC)
160 0% - 65% RH.
140
120 Influence:
100  µ encreased with no. of
μ [-]

80 layers
60  Influence from adhesive
 Board structure (slots,
40
holes)
20
0
Variant es
1 10 11 12 13
1 = lamellas glued,10 = not glued ,
Distance between lamellas: 11 = 5mm, 12 = 10mm, 13 = 30mm

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


Influence of board structure on thermal
conductivity
CLT from spruce: (Bader et al. 2007)

radial tangential without orientation
thermal conductivity (W/mK)


Thermal conductivity from CLT:
influence from the distance between lamellas

0.110
0.105
0.100
ּ K]
λ [W/m◌

0.095
0.090
0.085
0.080
10 11 0 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


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


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

Slots in the surface
before gluing:
climatization under
20oC/35% or
20oC/65%
without slots
not cracks detected
(compression stresses)
Slots in the middle layer


Modeling of moisture transfer and
moisture induced stresses-warping
(PhD: Gereke 2009)
Total strain:
• elastic: Hooke law
• Moisture induced: swelling
• Mechano- sorptiv effect

   el      
   
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)

AR: growth ring angle
0-tangential
90-radial

LR: Lamella ratio

2  a De
LR 
a Pl


3. Examples for using from CLT


Prefabricated house (Nägeli /CH)


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


one family house (Pius Schuler/CH)


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)


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


Thanks for your atention

IfB, wood physics


Session 21 ic2011 niemz

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Session 21 ic2011 niemz