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UNIVERSITYFREIBURG INSTITUTE for FOREST UTILIZATION and WORK SCIENCE IUFRO Division 5 Conference 5.04.06 – Wood drying Strength and long term durability.

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Presentation on theme: "UNIVERSITYFREIBURG INSTITUTE for FOREST UTILIZATION and WORK SCIENCE IUFRO Division 5 Conference 5.04.06 – Wood drying Strength and long term durability."— Presentation transcript:

1 UNIVERSITYFREIBURG INSTITUTE for FOREST UTILIZATION and WORK SCIENCE IUFRO Division 5 Conference – Wood drying Strength and long term durability of glued laminated timber from European Beech Denny OHNESORGE

2 INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 1 UNIVERSITYFREIBURG Authors/Institution Denny OHNESORGE* and Gero BECKER Albert-Ludwig-University Freiburg Institute of Forest Utilization and Work Science Werthmannstr. 6 D Freiburg, Germany Web:http://www.forst.uni-freiburg.de/fobawi Strength and long term durability of glued laminated timber from European Beech Part of the European project INNOBEECH

3 INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 2 UNIVERSITYFREIBURG Background information European Beech 60cm 85cm

4 INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 3 UNIVERSITYFREIBURG 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

5 INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 4 UNIVERSITYFREIBURG 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

6 INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 5 UNIVERSITYFREIBURG 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)

7 INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 6 UNIVERSITYFREIBURG 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) Acknowledgment:

8 INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 7 UNIVERSITYFREIBURG I. Methods Tests on gluability of European Beech acc. to European standards Matching &MaterialTest variantsEvaluation Lamellas from 28 Beech logs 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 I.Pre-study on glueability II.Test on delamination Test wood failure (%) strength [N/mm²] trans- verse tensile strength shear strength N-N = No red heart N-R = One red heart R-R = Both red heart dried steamed

9 INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 8 UNIVERSITYFREIBURG I. Results – pre-study Tests on short term strength acc. to European standards DIN EN Glued laminated timber – shear tests of glue lines Gluing line force direction force direction Gluing line force direction EN 302-3:2004 Determination of the acid damage… … transverse tensile strength (Picea)

10 INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 9 UNIVERSITYFREIBURG I. Results – pre-study Compression shear strength Higher StDiv ! Limit acc. to EN 301 A1 - A3 -

11 INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 10 UNIVERSITYFREIBURG I. Results – pre-study Transverse tensile strength Limit acc. to EN Limit = 80% of control ! A1 - A3 -

12 INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 11 UNIVERSITYFREIBURG 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

13 INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 12 UNIVERSITYFREIBURG 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:

14 INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 13 UNIVERSITYFREIBURG 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:

15 INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 14 UNIVERSITYFREIBURG 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

16 INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 15 UNIVERSITYFREIBURG II. Methods Tests on gluability of European Beech acc. to European standards Matching &MaterialTest variantsEvaluation II.Test on delamination dried Test delamination (%) against: - red heartwood - lamella thickness - assembly time - annual ring angle 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 I.Pre-study on glueability wood failure (%) strength [N/mm²] trans- verse tensile strength shear strength 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 heart R-R = Both red heart lamella thickness (closed) assembly time used glue: MUF lowest del. level delami- nation acc. to DIN 391: Scheme C

17 INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 16 UNIVERSITYFREIBURG II. Results – delamination tests Influence of red heartwood on the delamination rate [%] Limit acc. to EN 301

18 INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 17 UNIVERSITYFREIBURG II. Results – delamination tests Influence of the (closed) assembly time on the delamination rate [%] Limit acc. to EN 301 ?

19 INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 18 UNIVERSITYFREIBURG II. Results – delamination tests Influence of the lamella thickness on the delamination rate [%] Limit acc. to EN 301

20 INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 19 UNIVERSITYFREIBURG II. Results – delamination tests Influence of the ring angle combination on the delamination rate [%] Limit acc. to EN 301 *RR – combiation of two radial glued lamellas (RH – radial/half tangential; TT – tangential/tangential combined lamellas) *

21 INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 20 UNIVERSITYFREIBURG 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.

22 INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 21 UNIVERSITYFREIBURG 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.

23 INSTITUTE for FOREST UTILIZATION and WORK SCIENCE 22 UNIVERSITYFREIBURG Thank you for your attention! More information about the mentioned project Innovation for Beech see


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