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IUFRO Division 5 Conference 5.04.06 – Wood drying

IUFRO Division 5 Conference 5.04.06 – Wood drying. Denny OHNESORGE. Strength and long term durability of glued laminated timber from European Beech. Authors/Institution. Denny OHNESORGE* and Gero BECKER. Strength and long term durability of glued laminated timber from European Beech.

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IUFRO Division 5 Conference 5.04.06 – Wood drying

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  1. IUFRO Division 5 Conference5.04.06 – Wood drying Denny OHNESORGE Strength and long term durability of glued laminated timber from European Beech

  2. 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: denny.ohnesorge@fobawi.uni-freiburg.deWeb: http://www.forst.uni-freiburg.de/fobawi • http://www.innobeech.uni-freiburg.de

  3. 60cm Background information 85cm European Beech

  4. 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. State of knowledge Relevant wood features for hardwood bonding – example Eur. Beech • Beech vs. Spruce • Parameter • Factor • Density (weight!) • Stiffness • Surface hardness • pH- value • shrinkage/swelling anisotropy • extractives (red heartwood) • x1.5 • x1.3 • x1.25 • x1.2 • x1.2 … 1.25

  6.  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) 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

  7. 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) 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) ?

  8. Aging: A 1 = normal climate A 3 = water soaked/ cycling climate N-N = No red heart dried shearstrength strength [N/mm²] N-R = One red heart Glues: PRF= Phenol-Resorcinol-Formaldehyde-Resin MUF= Melamine-Urea-Formaldehyde-Resin PUR= Polyurethane-Adhesive steamed wood failure (%) R-R = Both red heart trans-versetensilestrength I. Methods • Tests on gluability of European Beech acc. to European standards Material Matching & Test variants Test Evaluation I. Pre-studyon glueability Lamellas from 28 Beech logs II. Test on delamination

  9. forcedirection Gluing lineforce direction Gluing line forcedirection 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)

  10. Higher StDiv ! Limit acc. to EN 301 I. Results – pre-study • Compression shear strength A3 - A1 -

  11. I. Results – pre-study • Transverse tensile strength   Limit = 80% of control ! Limit acc. to EN 302-3 A3 - A1 -

  12. 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. 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) 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 ?

  14. 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)

  15. Measurement of annual ring angle for each lamella N-N = No red heart N-R = One red heart R-R = Both red heart 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

  16. Aging: A 1 = normal climate A 3 = water soaked/ cycling climate N-N = No red heart dried shearstrength strength [N/mm²] N-R = One red heart Glues: PRF= Phenol-Resorcinol-Formaldehyde-Resin MUF= Melamine-Urea-Formaldehyde-Resin PUR= Polyurethane-Adhesive steamed wood failure (%) R-R = Both red heart trans-versetensilestrength lamella thickness (closed) assembly time  used glue: MUF N-N = No red heart 38 lowest del. level 35 32 N-R = One red heart 29 delami-nationacc. to DIN 391: Scheme “C” dried R-R = Both red heart II. Methods • Tests on gluability of European Beech acc. to European standards Material Matching & Test variants Test Evaluation I. Pre-studyon glueability Lamellas from 28 Beech logs • delamination (%) against: • red heartwood • lamella thickness • assembly time • annual ring angle II. Test on delamination

  17. II. Results – delamination tests • Influence of red heartwood on the delamination rate [%] Limit acc. to EN 301

  18. ? II. Results – delamination tests • Influence of the (closed) assembly time on the delamination rate [%] Limit acc. to EN 301

  19. II. Results – delamination tests • Influence of the lamella thickness on the delamination rate [%] Limit acc. to EN 301

  20. 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. 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. 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. 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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