universityfreiburg institute for forest utilization and work science iufro division 5 conference...
TRANSCRIPT
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
INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 3UNIVERSITY FREIBURG
Background information
European Beech
60cm
85cm
INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 4UNIVERSITY FREIBURG
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
INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 5UNIVERSITY FREIBURG
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
INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 6UNIVERSITY FREIBURG
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)
INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 7UNIVERSITY FREIBURG
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:
INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 8UNIVERSITY FREIBURG
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
INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 9UNIVERSITY FREIBURG
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)
INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 10UNIVERSITY FREIBURG
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
I. Results – pre-study
Compression shear strengthHigherStDiv !
Limit acc. to EN 301
A1 - A3 -
INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 11UNIVERSITY FREIBURG
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
I. Results – pre-study
Transverse tensile strength
Limit acc. to EN 302-3
Limit = 80% of control !
A1 - A3 -
INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 12UNIVERSITY FREIBURG
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
INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 13UNIVERSITY FREIBURG
Research questions and objectives
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:
INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 14UNIVERSITY FREIBURG
Research questions and objectives
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)
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:
INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 15UNIVERSITY FREIBURG
Research questions and objectives
II. Analyses of delamination to evaluate long term durability of bonding
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
INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 16UNIVERSITY FREIBURG
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”
INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 17UNIVERSITY FREIBURG
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 [%]
Limit acc. to EN 301
INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 18UNIVERSITY FREIBURG
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 [
%]
II. Results – delamination tests
Influence of the (closed) assembly time on the delamination rate [%]
Limit acc. to EN 301
?
INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 19UNIVERSITY FREIBURG
II. Results – delamination tests
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 [
%]
INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 20UNIVERSITY FREIBURG
II. Results – delamination tests
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)
*
INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 21UNIVERSITY FREIBURG
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.
INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 22UNIVERSITY FREIBURG
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.
INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 23UNIVERSITY FREIBURG
Thank you for your attention!
More information about the
mentioned project
“Innovation for Beech” see
http://www.innobeech.uni-freiburg.de