Transcript Folie 1
Denny OHNESORGE
IUFRO Division 5 Conference 5.04.06 – Wood drying
Strength and long term durability of glued laminated timber from European Beech
INSTITUTE for FOREST UTILIZATION and WORK SCIENCE UNIVERSITY FREIBURG
Authors/Institution
Denny OHNESORGE* and Gero BECKER
Strength and long term durability of glued laminated timber from European Beech
Part of the European project INNOBEECH
Albert-Ludwig-University Freiburg Institute of Forest Utilization and Work Science Werthmannstr. 6 D-79085 Freiburg, Germany E-mail: Web: [email protected]
http://www.forst.uni-freiburg.de/fobawi http://www.innobeech.uni-freiburg.de
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Background information
85cm
European Beech
60cm INSTITUTE for FOREST UTILIZATION and WORK SCIENCE UNIVERSITY FREIBURG 2
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
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State of knowledge
Relevant wood features for hardwood bonding – example Eur. Beech Parameter Beech vs. Spruce
• • • • • •
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
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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 UNIVERSITY FREIBURG 5
Research questions and objectives
I. Pre study evaluating “short term” strength of glued Beech timber
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) ?
Acknowledgment:
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)
Ma ter ials Sci ence & Technolog y
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I. Methods
Tests on gluability of European Beech acc. to European standards
Material
I. Pre-study on glueability dried steamed Lamellas from 28 Beech logs
Matching &
N-N =
No red heart
N-R =
One red heart
R-R =
Both red heart Test variants
Aging: A 1 =
normal climate
A 3
= water soaked/ cycling climate
Glues: PRF=
Phenol-Resorcinol Formaldehyde-Resin
MUF=
Melamine-Urea Formaldehyde-Resin
PUR=
Polyurethane-Adhesive Test Evaluation
shear strength strength [N/mm²] wood failure (%) trans verse tensile strength II. Test on delamination INSTITUTE for FOREST UTILIZATION and WORK SCIENCE UNIVERSITY FREIBURG 7
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 EN 302-3:2004 Determination of the acid damage… … transverse tensile strength (Picea) force direction Gluing line force direction Gluing line INSTITUTE for FOREST UTILIZATION and WORK SCIENCE force direction UNIVERSITY FREIBURG 8
I. Results – pre-study
Compression shear strength
N-N 6 4 2 0 20 18 16 14 12 10 8 PRF MUF A1 normal climate PUR N-R R-R PRF MUF A3 changed climate PUR
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Limit acc. to EN 301 FREIBURG 9
I. Results – pre-study
Transverse tensile strength
N-N
Limit acc. to EN 302-3
4 3 2 1 0 12 11 10 9 8 7 6 5 PRF MUF PUR A1 normal climate N-R PRF MUF A3 changed climate PUR
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R-R
UNIVERSITY
Limit = 80% of control !
FREIBURG 10
Conclusions
I. Pre study: “short term” strength
All A1-conditioned requirements: samples Service class reached 1 strength application red heartwood is possible with all adhesive types of values Beech well above containing 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
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Research questions and objectives
II. Analyses of delamination to evaluate long term durability of bonding
Does delamination results can be improved by considering different bonding and wood parameters ?
- red heartwood combination - lamella thickness (38, 35, 32, and 29mm) - annual ring angle - (closed) assembly time
Acknowledgment:
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) INSTITUTE for FOREST UTILIZATION and WORK SCIENCE UNIVERSITY FREIBURG 12
Research questions and objectives
II. Analyses of delamination to evaluate long term durability of bonding
Does delamination results can be improved by considering different bonding and wood parameters ?
- red heartwood combination - lamella thickness (38, 35, 32, and 29mm) - annual ring angle - (closed) assembly time
Acknowledgment:
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) INSTITUTE for FOREST UTILIZATION and WORK SCIENCE UNIVERSITY FREIBURG 13
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 heart
R-R =
Both red heart Measurement of annual ring angle for each lamella
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II. Methods
Tests on gluability of European Beech acc. to European standards
Material
I. Pre-study on glueability dried steamed
Matching &
N-N =
No red heart
N-R =
One red heart
R-R =
Both red heart Test variants
Aging: A 1 =
normal climate
A 3
= water soaked/ cycling climate
Glues: PRF=
Phenol-Resorcinol Formaldehyde-Resin
MUF=
Melamine-Urea Formaldehyde-Resin
PUR=
Polyurethane-Adhesive
Lamellas from 28 Beech logs dried N-N =
No red heart
N-R =
One red heart
R-R =
Both red heart
lamella thickness 35 32 29 38 II. Test on delamination (closed) assembly time
used glue: MUF INSTITUTE for FOREST UTILIZATION and WORK SCIENCE
Test
UNIVERSITY
Evaluation
shear strength strength [N/mm²] wood failure (%) trans verse tensile strength delami nation acc. to DIN 391: Scheme “C” delamination (%) against:
-
red heartwood
-
lamella thickness
-
assembly time
-
annual ring angle lowest del. level FREIBURG 15
II. Results – delamination tests
Influence of red heartwood on the delamination rate [%] 24% 22% 20% 18% 16% 14% 12% 10% 8% 6% 4% 2% 0% N-N N-R red heartwood combination R-R INSTITUTE for FOREST UTILIZATION and WORK SCIENCE UNIVERSITY Limit acc. to EN 301 FREIBURG 16
II. Results – delamination tests
Influence of the (closed) assembly time on the delamination rate [%] 40% 35% 30% 25% 20% 15% 10% 5% 0% ?
Limit acc. to EN 301 10 20 30 40 70 80 closed assembly time [min] 120 160 INSTITUTE for FOREST UTILIZATION and WORK SCIENCE UNIVERSITY FREIBURG 17
II. Results – delamination tests
Influence of the lamella thickness on the delamination rate [%] 40% 35% 30% 25% 20% 15% 10% 5% 0% 29 32 35 Lamella thickness [mm] 38 Limit acc. to EN 301 INSTITUTE for FOREST UTILIZATION and WORK SCIENCE UNIVERSITY FREIBURG 18
II. Results – delamination tests
Influence of the ring angle combination on the delamination rate [%] 50% 45% 40% 35% 30% 25% 20% 15% 10% 5% 0% Limit acc. to EN 301 RR * RH RT HH TH TT annual ring angle combination *RR – combiation of two radial glued lamellas (RH – radial/half tangential; TT – tangential/tangential combined lamellas) INSTITUTE for FOREST UTILIZATION and WORK SCIENCE UNIVERSITY FREIBURG 19
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.
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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.
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Thank you for your attention!
More information about the mentioned project “Innovation for Beech” see http://www.innobeech.uni-freiburg.de
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