iufro division 5 conference 5.04.06 – wood drying

UNIVERSITY FREIBURGINSTITUTE for FOREST UTILIZATION and WORK SCIENCE

IUFRO Division 5 Conference

5.04.06 – Wood drying

Strength and long term durability of glued laminated timber

from European Beech

Denny OHNESORGE

INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 2UNIVERSITY FREIBURG

Authors/Institution

Denny OHNESORGE* and Gero BECKER

Albert-Ludwig-University FreiburgInstitute of Forest Utilization and Work ScienceWerthmannstr. 6D-79085 Freiburg, Germany

E-mail: [email protected]: http://www.forst.uni-freiburg.de/fobawi

http://www.innobeech.uni-freiburg.de

Strength and long term durability of glued laminated timber from European Beech

Part of the European project INNOBEECH


Background information

European Beech

60cm

85cm


Background information

European Beech is most important hardwood in Europe with a growing old stock in Germany

Currently, its timber is mainly used in furniture, floorings, and packaging – hardly in constructions

In order to find new applications for European Beech, recently several innovative products were investigated beside others:

Beech as glued laminated timber for constructions

With 98%, today's gluelam production in Germany, Switzerland and Austria is dominated by softwoods (Inquiry in 2007)

This applies also to adhesion technology, manufactory equipment, education as well as legislation procedures for structural bonding, which is all designed for production of softwood gluelams

Glued laminated hardwood elements are not regulated construction products according to the German building regulations


State of knowledge

Beech vs. SpruceParameter

• Density (weight!)

• Stiffness

• Surface hardness

• pH- value

• shrinkage/swelling anisotropy

• extractives (red heartwood)

Factor

x1.5

x1.3

x1.25

x1.2

x1.2 … 1.25

Relevant wood features for hardwood bonding – example Eur. Beech


State of knowledge

What abou bonding hardwoods like Beech ?

Bonding parameters has to be adapted like:

adhesive amount, adhesive application on both sides of

lamella, assembly time, gluing pressure and pressing time

Several tests on glueability showed good bonding strength results

under normal climate conditions for both – light and red-hearted

Beech wood

but tests on delamination were reported

negative for both light and red-hearted Beech

wood

for example: above 50% delamination for red-

hearted Beech wood (Aicher and Reinhardt, 2006)


Research questions and objectives

Does red heartwood has a different adhesion behavior than normal

Beech in

- dry conditions ?

- under the impact of moisture and temperature cycling (ageing) ?

- when glued with different structural adhesives (PRF, MUF, PUR) ?

I. Pre-study evaluating “short term” strength of glued Beech timber

Tests were carried out at the Wood Laboratory of the

Swiss Federal Laboratory for Materials Testing and Research

(in close collaboration

with Dr. Klaus Richter)

Materials Science&Technology

Acknowledgment:


I. Methods

Tests on gluability of European Beech acc. to European standards

Matching &Material Test variants Evaluation

Lamellas from 28 Beech logs

Aging:A 1 = normal climateA 3 = water soaked/

cycling climate

Glues:PRF= Phenol-Resorcinol-Formaldehyde-ResinMUF=Melamine-Urea-Formaldehyde-ResinPUR=Polyurethane-Adhesive

I. Pre-studyon glueability

II. Test on delamination

Test

wood failure (%)

strength [N/mm²]

forcedirection

Gluing line

forcedirection

forcedirection

Gluing line

forcedirection

trans-verse

tensilestrength

Gluing line

force direction

Gluing line

force direction

shearstrength

N-N = No red heart

N-R = One red heart

R-R = Both red heart

dried

steamed


I. Results – pre-study

Tests on short term strength acc. to European standards

DIN EN 392-1 Glued laminated timber – shear tests of glue lines

Gluing line

force direction

forcedirection

Gluing line

forcedirection

EN 302-3:2004 Determination of the acid damage…

… transverse tensile strength (Picea)


0

2

4

6

8

10

12

14

16

18

20

PRF MUF PUR PRF MUF PUR

normal climate changed climate

stre

ngth

in N

/mm

²

N-N N-R R-R


Compression shear strengthHigherStDiv !

Limit acc. to EN 301

A1 - A3 -


0

1

2

3

4

56

7

8

9

10

11

12

PRF MUF PUR PRF MUF PUR

normal climate changed climate

stre

ngth

in N

/mm

²

N-N N-R R-R


Transverse tensile strength

Limit acc. to EN 302-3

Limit = 80% of control !

A1 - A3 -


Conclusions

I. Pre-study: “short term” strength

All A1-conditioned samples reached strength values well above requirements: Service class 1 application of Beech containing red heartwood is possible with all adhesive types

Under moisture impact, PRF adhesives form the most reliable bonds at red-hearted surfaces

MUF and PUR bonds at red-hearted surfaces are less moisture resistant under transverse tensile stresses, although wood failure rates are considerably high

The observed higher variability in shear strength of red heartwood samples bonded with light colour adhesives indicates an influence of accessory compounds on the boundary layer. The variable surface distribution of accessory compounds would be an answer

The sufficiently high average shear strength values derived in our study support the potential application of red-hearted Beech in glued products for structural proposes



Does delamination results can be improved by considering different bonding and wood parameters ?

II. Analyses of delamination to evaluate long term durability of bonding

- red heartwood combination - lamella thickness

(38, 35, 32, and 29mm)

- annual ring angle - (closed) assembly time

One part of the test samples were from Beech gluelam beams,

made for shear strength tests in component size.

Those tests were carried out in close collaboration with the

German Federal Laboratory for Materials Testing

(Dr. Simon Aicher)

Acknowledgment:



Does delamination results can be improved by considering different bonding and wood parameters ?


- red heartwood combination - lamella thickness

(38, 35, 32, and 29mm)

One part of the test samples were from Beech gluelam beams,

made for shear strength tests in component size.

Those tests were carried out in close collaboration with the

German Federal Laboratory for Materials Testing

(Dr. Simon Aicher)

- annual ring angle - (closed) assembly time

Acknowledgment:




A. 14 Samples from

industrial Beech gluelam beams

B. 15 Samples from

laboratory Beech gluelam beams

N-N = No red heart

N-R = One red heartR-R = Both red heart

Measurement of

annual ring angle

for each lamella


II. Methods

Tests on gluability of European Beech acc. to European standards

Matching &Material Test variants Evaluation

II. Test on delamination

dried

Test

delamination (%) against:- red heartwood - lamella thickness- assembly time- annual ring angle

Aging:A 1 = normal climateA 3 = water soaked/

cycling climate

Glues:PRF= Phenol-Resorcinol-Formaldehyde-ResinMUF=Melamine-Urea-Formaldehyde-ResinPUR=Polyurethane-Adhesive

I. Pre-studyon glueability

wood failure (%)

strength [N/mm²]

forcedirection

Gluing line

forcedirection

forcedirection

Gluing line

forcedirection

trans-verse

tensilestrength

Gluing line

force direction

Gluing line

force direction

shearstrength

N-N = No red heart

N-R = One red heart

R-R = Both red heart

dried

steamed

Lamellas from 28 Beech logs N-N = No

red heart

N-R = One red heartR-R = Both red heart

lamella thickness

(closed) assembly time

used glue: MUF

2932

3538

lowest del. level

delami-nationacc. to

DIN 391:Scheme

“C”


0%

2%

4%

6%

8%

10%

12%

14%

16%

18%

20%

22%

24%

N-N N-R R-R

red heartwood combination

Del

amin

atio

n [

%]

II. Results – delamination tests

Influence of red heartwood on the delamination rate [%]



0%

5%

10%

15%

20%

25%

30%

35%

40%

10 20 30 40 70 80 120 160

closed assembly time [min]

De

lam

ina

tio

n [

%]


Influence of the (closed) assembly time on the delamination rate [%]


?



Influence of the lamella thickness on the delamination rate [%]

Limit acc. to EN 3010%

5%

10%

15%

20%

25%

30%

35%

40%

29 32 35 38

Lamella thickness [mm]

Del

amin

atio

n [

%]



Influence of the ring angle combination on the delamination rate [%]

Limit acc. to EN 3010%

5%

10%

15%

20%

25%

30%

35%

40%

45%

50%

RR RH RT HH TH TT

annual ring angle combination

De

lam

ina

tio

n [

%]

*RR – combiation of two radial glued lamellas (RH – radial/half tangential; TT – tangential/tangential combined lamellas)

*


Conclusions

II. Delamination test: “long term durability”

Delamination test showed a major influence of different bonding

parameters and wood features on the delamination rate

The negative influence of red heartwood could not be confirmed.

The interaction between tested parameters have to be analysed!

A major positive effect could be observed for the reduction of the lamella

thickness.

An increase of the (closed) assembly time up to 40 min has a positive

impact on the delamination rate.

A small annual ring angle can improve the results in the same way.


Outlook

Today, glued laminated

hardwood elements are still

not regulated constructions

products according to

German building regulations.

But, European Beech wood

can fulfil the requirements

for indoor applications, if

bonding will be adapted and

wood parameters will be

considered.


Thank you for your attention!

More information about the

mentioned project

“Innovation for Beech” see

http://www.innobeech.uni-freiburg.de

iufro division 5 conference 5.04.06 – wood drying

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