1. The effects of planting density on the structural timber properties of 23-year-old Irish-grown Sitka spruce
Karlo Simic 1 , Vilius Gendvilas 2 , Conor O’Reilly 2 , Maarten Nieuwenhuis 2 , Annette Harte 1
1 College of Engineering and Informatics, National University of Ireland, Galway, University Rd., Galway, Ireland
2 UCD Forestry, School of Agriculture and Food Science, University College Dublin, Belfield Dublin 4, Ireland

2. Contents overview Introduction Materials and methods summary
Results from strength grading machine for sawn timber from different planting densities
Preliminary results for MOE, bending strength, density and visual inspection
Conclusion

3. Introduction
“…more appropriate for a forestry conference than a civil engineering conference…”
Sustainable construction – use of renewable native resources
¾ of the national forest estate consists of trees of 30 years old or less
Sitka spruce in Ireland – covers 5.5 % of the total land area
Study aim - to explain the effects of different initial planting densities and tree characteristics on structural timber quality

4. Timber quality - Grade-determining properties
Strength classes are defined by:
Bending strength (lower 5th percentile)
Modulus of elasticity in bending (mean)
Density (lower 5th percentile)
Visual override (fissures, warp, defects)
EN338

5. Site Forest location – Co. Leitrim 23-year-old in the time of felling
12 plots selected
10 different planting densities

6. Selected site - Planting density groups
Low planting density group
1550 – 1850 stems/ha
Standard planting density group 2300 – 2550 stems/ha
High planting density group
3100 – 3700 stems/ha

7. Tree cutting 10 m log Butt Middle Top 3 m log 3 m log 3 m log 1 2 3 4
4 x 10 cm discs

8. Test categories and sample sizes
Logs
211 pcs
Boards
904 pcs
Small samples
72 pcs

9. Sawn timber 198 logs cut – 9 cutting patterns – 904 boards in total
2 cross sectional sizes:
44x100 – 477 boards
35x75 – 427 boards

10. Sawn timber measurements
Dynamic MOE on “green” boards using the MTG grader
Timber above FPS
MOE measurements with the Microtec Goldeneye 702 X-ray grader
Timber at 18±2% M.C.
Dynamic MOE on dry boards using the MTG grader
Timber at 12% M.C.

11. Ongoing measurements on sawn timber
MOE using Cook Bolinders grading machine
Local MOE (“pure bending”), global MOE and bending strength using 4-point bending test (EN408:2010)
Visual inspection (IS 127)
Timber density
Moisture content

12. Results from the strength grading machine
Edyn,undried
35x75
44x100
Mean Edyn,undried [MPa]
Board size
35x75
44x100
Low PDG
7652 (1316)
7097 (1244)
Standard PDG
7874 (1479)
7666 (1298)
High PDG
7939 (1354)
8341 (1315)
Sample size
421
477

13. Relationship between Edyn,12 and board origin
Low PDG
Standard PDG
High PDG
3rd log
7880 (818)
8130 (1247)
8682 (1056)
2nd log
7854 (901)
8354 (931)
8671 (1084)
1st log
6824 (1289)
7994 (1348)
8473 (1600)
Mean (SD) [MPa]
44x pcs

14. Timber density – Preliminary results
ρclear wood,12% M.C.
ρboard,12% M.C.
44x100
5- percentile
ρclear wood,12% [kg/m3]
5-percentile
ρboard,12% [kg/m3]
Low PDG
312
315
Standard PDG
341
365
High PDG
321
Sample size
148
411

15. Timber MOE and bending strength – Preliminary results
Elocal (EN 408)
fm (EN 408)
44x100
Mean Elocal [MPa]
5-percentile fm [MPa]
Low PDG
7228 (1690)
17.42
Standard PDG
8113 (1844)
21.71
High PDG
8352 (1659)
27.53
Sample size
148
148 pcs

16. Visual inspection: Twist – Preliminary results
Reject
Structural timber
No pith
Pith present
Low PD group
Standard PD group
High PD group

17. Conclusions
Planting density – significant influence on timber structural properties
Timber quality models under development
Twist – one of the major constraints in using structural timber from young Sitka spruce forests
Production of CLT – an opportunity for warped material from young trees?

18. Acknowledgments

19. Thank you for your attention!