eth zurich institute for building materials (ifb), wood physics group ; [email protected] © eth...

ETH Zurich

Institute for Building Materials (IfB), Wood Physics Group

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

Solid wood panels – a new wood based material with high value added Peter Niemz

211/2006 Peter Niemz, IfB Wood Physics Group, [email protected]

Outline

1. Introduction2. Modelling of Properties

2.1 Mechanical Properties• MOE• MOR

Experimental Tests2.2Physical Properties • Sorption• Swelling• Warping• Internal stresses

3. Conclusions


1. Introduction

x 1

x 2

x 3

3

32

31

13

12

1

23

2

21

(z)

(x)

(y)

What is a solid wood panel?3 or 5 layer cross laminated board (system from plywood)

Board: up to 0.5m (thickness)x3m x15m


What is a solid wood panel?• Solid wood panels represent a new multilayer material based on boards, which are glued together crosswise, in most cases spruce wood is used

• Used more and more in timber constructions providing a high value added

• The utilisation of this kind of panel gains in importance in the Swiss, German and Austrian building industry

• It is possible to vary the properties of the panels through panel configuration


Utilisation of solid wood panels as building material


Industrial prefabrication (Schilliger AG, Switzerland)


Roof constructions with solid wood panels


House built with solid wood panels


2. Modelling of Properties

2.1 Mechanical Properties

The load direction

surface layer parallel

surface layer perpendicular

(II) () MOE, pure bending

Eb(II) (N/mm2) Eb()

(N/mm2)

Shearing strength (rolling shear)

13(rol. shear) (N/mm2) 231)

(N/mm2)

Shear module

G13 (N/mm2) G231)

(N/mm2)

Bending perpendicular to the surface


rolling shear (r-t) in middle layer


a) Modulus of elasticity, if L/h>35 Navier-Bernoulli pure bending

33)2(

13

3)1(

1,22

1

v

v

v

vboardb

L

LE

L

LEE

E1 (1): Elastic module 1 (surface layer) with load in direction 1

E1 (2): Elastic module of layer 2 (middle layer) with load in direction 1

Eb,ges: Elastic module of cross section

Lv: Relation of lamellas-thicknesses; Lv= h (2)/h (1)

h (1): Thickness of the surface layerh (2): Thickness of the middle layer

(N/mm2)

MOE (Young’s modulus)MOE (Young’s modulus)

For surface layer orientation parallel to the longitudinal axis:

E1 (1) = EL = 11000 N/mm2; v = 15%E1 (2) = ER/T = 450 N/mm2

For surface layer orientation perpendicular to the longitudinal axis:E2 (1) = ER/T = 450 N/mm2

E2 (2) = EL= 11000 N/mm2; v = 20% (lower quality in the middle layer)


b) Modulus of elasticity, if L/h<35 (parallel)

c

EE b

bx

1

2

2)2(

13

)1(13

Re2

)2(1

)1(13

3)1(

1

21224/

2

v

v

v

Su

v

vL

L

LG

L

GhL

EEL

LEK

c

(N/mm2)

Eb-E by pure bending

Exb _ E diminished by shearing

E = f (Bending + shearing)


calculated influence of the lamella ratio on the MOE

(pure bending)

0

2000

4000

6000

8000

10000

12000

0.0 1.0 2.0 3.0 4.0 5.0thickness middle/surface layer

MO

E

Eb,

boar

d (N

/mm

2 )

Eb,équi(II)

Eb,équi(per)

cv=15%: surface layer parallel, cv=±20% surface layer perpendicular


Tests on an entire board, supported at all edges

(together with the Empa/Dübendorf, Dep. of structural Engineering)


Overview of panel tests

Lod Board structure No

boards

A 4 loads

1 10/50/10 mm 6

A 4 loads

2 25/20/25 mm 6

B 1 load, centric

1 10/50/10 mm 6

C 1 load, excentric

1 10/50/10 mm 6

Overview of panel tests


Failure of an entire board, not failure by rolling shear


Producer n Min[N/mm2]

Mean[N/mm2]

Max[N/mm2]

Median[N/mm2]

s[N/mm2]

x05

[N/mm2]

v[%]

Beam tests

A 70 18.7 36.5 50.4 37.6 6.18 25.5 16.9

B 78 20.3 39.9 54.4 41.1 6.71 28.0 16.8

tests at entire board

A 12 35.1 50.7 61.4 50.0 8.20 35.1 16.2

B 12 49.6 59.8 68.6 59.5 5.86 48.0 9.80

Failure stresses determined from beam and panel tests

• maximal strain tested in tensile zone from the board: 2-3%, • solid wood 1%

publication „Holz als Roh und Werkstoff“ (2007), test of different models


2.2 Physical Properties

a) Equilibrium moisture content (calculated with Hailwood Horrobin)


sample m2/g UFS UP UM

MHP-3-27pa 265 20.49 13.01 7.47

MHP-3-27pe 249 21.06 14.03 7.04

MHP-3-30pa 269 20.86 13.27 7.60

MHP-3-30pe 235 22.43 15.79 6.64

Surface layer: Pa: parallel; Pe: perpendicular

Calculated parameters for sorption Calculated parameters for sorption (Hailwood Horrobin)(Hailwood Horrobin)

=specific surface, up= polymolecular water, um= monomolecular water


b) Swelling (board thickness 60mm)

• thickness 0,3-0,5%/%

• length 0,045 %/%, (20/20/20)

0,016 %/%, (10/40/10) 0,021%/%, (12/12/12/12/12)

Influence from board structure (relation surface/middle layer)


c) Diffusion resistence

• Adhesive types tested : PVA, UF, PUR (2 types), Resorcin• 3 and 5 layer solid wood panels with different lamella ratios

0% 12%0%

0% 0%

12%

12%12%

Trockenm ittelS ilikagel

K lim a aussen:20°C / 65% rF

K lim a innen :20°C / 0% rF

Theore tische H olz feuchtigke it

V ersuchsbeg inn V ersuchsende


y = 20.913x - 4.3976

R2 = 0.883

y = 34.993x + 74.066

R2 = 0.8972

-10.0

40.0

90.0

140.0

190.0

240.0

290.0

340.0

0 1 2 3 4 5 6

no. of gluelines

dif

us

ion

re

sis

ten

ce

μ [

-]

wet cup (100%/65%)

dry cup (0%-65%rH)

Influence of the number of gluelines (for 1K PUR)


• The water vapour diffusion resistance is strongly related to the number of glue layers per panel thickness

• No influence on the water vapour diffusion resistance by the utilisation of different types of adhesives was found

• The diffusion resistance decreased while the EMC increased

Results diffusion resistance


d) Internal stresses

0 10 20 30 40 50 60

Dicke (mm)

0

1

2

3

4

5

6

7

8

9

10

Feu

chte

geh

alt

(Vo

l%)

0

2

4

6

8

10

12

14

16

18

20

22

Masse%

77

177177

0 0

2828

Zeit in Tagen

Zeitlicher Verlauf der gemessenen HolzfeuchtewerteMassivholzplatte, Lagerung im Konstantklima

Moisture distribution in wood panels 2oC/90% RH


Result:Internal cracks or warping from boards

different EMC during production and use

different EMC at both sides from the board


Hindered shrinking of a 3-layer solid wood panel


Modelling of warping and internal stresses in glued wood

a) example: 3-layer parquet element, oak-spruce-spruce

veneer; thickness: 14mm (3/8/3mm), diploma thesis

b) 2006 we started a PHD about internal stresses

in solid wood panels


Moisture transfer Transfer model, Diffusion 1D

2

31

D

D

e ff.oak

e ff.p ine

u a ir = u top surface

u a ir bottom surface= u

0.1m m U F res in

0.1m m U F res in

Model in ABAQUS

x

uuD

xt

uW )(

u in itia l u final

uzh

h

oak

pine

100

.0

.1.2

plate

plateuplateuplate m

mmu

)

1001()

1001( 2

.02

.0.pine

pinepineoak

oakoakplateu

ubh

ubhm

pineoak

pineoakpine

pineoak

oak

ABAQUS hhn

hhnu

hu

hn

u

100

~1

100

~1

Iteration-method

simplification- Deff constant- without glueline- without surface material

Calculation of the influence from glue lines is possible, but material parameters are necessary


Model A: Warping from parquetABAQUS FE Model

2

3

1 u2=0

u1= 0A (10 /14 .2 /13)

B (94 /14 .2 /13 )

u3=0

v B

A

M ois tu re exchangelim ited to the top su rface

94

Model- 3D brick Elements- 20 Points, quadr.

interpolation- mash size 2mm

Beam theory

L 1L 2L 3L e k v

N

N 2

N 3

L e kv

M

yc

1

(a) (b)

12

3

ekv

u i

ekv

M 1

M 2

M 3

beAx

2min e

x


0 20 40 60 80 100 1200

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Time [days]

Cu

pp

ing

v [m

m]

Beech

Oak

Ash

0 20 40 60 80 100 1200

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Time [days]

Cu

pp

ing

v [m

m]

Beech

Oak

Ash

0 20 40 60 80 100 1200

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Time [days]

Cu

pp

ing

v [m

m]

Beech

Oak

Ash

0 20 40 60 80 100 1200

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Time [days]

Cu

pp

ing

v [m

m]

Beech

Oak

Ash

0 20 40 60 80 100 1200

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Time [days]

Cu

pp

ing

v [m

m]

Beech SL 3.6mm

Oak SL 3.6mm

Ash SL 3.6mm

0 20 40 60 80 100 1200

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Time [days]

Cu

pp

ing

v [m

m]

Angle = 30degAngle = 45 degAngle = 0 degAngle = 90 deg

0 20 40 60 80 100 1200

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Time [days]

Cu

pp

ing

v [m

m]


0 20 40 60 80 100 1200

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Time [days]

Cu

pp

ing

v [m

m]


0 20 40 60 80 100 1200

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Time [days]

Cu

pp

ing

v [m

m]

0 20 40 60 80 100 1200

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Time [days]

Cu

pp

ing

v [m

m]


Influence of the grain angle in the surface layer


0 20 40 60 80 100 1200

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Time [days]

Cu

pp

ing

v [m

m]

Surface layer 2.6mm

Surface layer 3.6mm

Surface layer 4.8mm

0 20 40 60 80 100 1200

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Time [days]

Cu

pp

ing

v [m

m]

Surface layer 4.8mm

Surface layer 3.6mm

Surface layer 2.6mm

0 20 40 60 80 100 1200

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Time [days]

Cu

pp

ing

v [m

m]

Surface layer 2.6mm

Surface layer 3.6mm

Surface layer 4.8mm

0 20 40 60 80 100 1200

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Time [days]

Cu

pp

ing

v [m

m]

Surface layer 4.8mm

Surface layer 3.6mm

Surface layer 2.6mm

Influence of the layer thicknesses


Model B: Stresses in the glue line and gap opening


Stress analysis (for parquet; investigations on solid wood panels are ongoing)

Longtime study cut A-A

-15 -10 -5 0 5 10 15 20 25-1

-0.5

0

0.5

1

1.5

2

Horizontal distance to middle gap [mm]

Ver

tica

l stre

sses

S2

2 [M

Pa]

L= 0,

R,T= 0

L= 0.1,

R,T= 0.8

L= 0.3,

R,T = 1.6

L= 1.5,

R,T= 7

A ABD

B

E CC

-15 -10 -5 0 5 10 15 20 25-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

Horizontal distance to middle gap [mm]

Sh

ea

r st

ress

es

S1

2 [M

Pa

]

L= 0,

R,T= 0

L= 0.1,

R,T= 0.8

L= 0.3,

R,T = 1.6

L= 1.5,

R,T= 7

Periodic loading increases the creeping , effect delamination can occur after several summer – winter cycles.


ongoing works


On-line testing free swelling hindered swelling

Testing of internal stresses


Results (spruce)

Swelling pressure

0 5 10 150

0.2

0.4

0.6

0.8

1

1.2

1.4

time [d]

pres

sure

pQ [k

N/m

m²]

Fichte (tangential)

Fichte (radial)

Fichte (longitudinal)

MDF (Plattenebene)

Dreischichtplatte


Results (spruce)

Free swelling

0 5 10 150

0.5

1

1.5

2

2.5

time [d]

swel

ling

α [%

/%]

Fichte (tangential)Fichte (radial)Fichte (longitudinal)MDF (Plattenebene)DSP (stehende Jahrringe)DSP (liegende Jahrringe)

00

0.05

0.1

0.15

0.2

0.25

0.3

0.35


3. Conclusions

Solid wood panels have a very high value added

(producer mostly saw mills)

Properties can be calculated

Scientifically interesting field of work


IfB, Wood Physics

Any Questions?

eth zurich institute for building materials (ifb), wood physics group ; [email protected] © eth...

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