Materials and Structures

, 51:143 | Cite as

Experimental investigation of the axial strength of glued-in rods in cross laminated timber

  • Boris Azinović
  • Erik Serrano
  • Miha Kramar
  • Tomaž PazlarEmail author
Original Article


This paper presents results from an experimental assessment of glued-in rods in cross laminated timber (CLT). For the purposes of the study more than 60 pull–pull tests were performed, where the specimens varied in terms of bonded-in length (from 80 to 400 mm), rod diameter (16–24 mm) and rod-to-grain angle (parallel and perpendicular). Several different failure modes that are not common for other applications of glued-in rods (e.g., a failure between CLT layers) were obtained for the analysed CLT specimens. It was found that these failure mechanisms can substantially influence the obtained ultimate tension loads. At the end, the experimental results were compared with empirical and semi-empirical equations for estimating the pull-out strength of glued-in rods in structural timber and glulam. The comparison showed that most of the existing equations overestimate the ultimate tension loads for specimens with the rod parallel to the grain and underestimate the ultimate tension load for specimens with the rod perpendicular to the grain. The results vary because the possible CLT failure modes were not included in previous studies. Further studies are proposed to improve the equations for glued-in rods in CLT.


Glued-in rods Cross laminated timber (CLT) Pull–pull experiment Glued-in length Rod-to-grain angle Failure mechanisms in CLT 



The authors gratefully acknowledge the European Cooperation in Science and Technology for funding the InnoRenew CoE project [Grant Agreement #739574] under the H2020 Spreading Excellence and Widening Participation Horizon2020 Widespread-Teaming program, and the financial support from the Slovenian Research Agency (research core Funding No. (P2-0273)).

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.

Ethical approval

The authors declare that there is no issue concerning ethical standards.

Informed consent

Informed consent was obtained from all individual participants included in the study.

Supplementary material

Supplementary material 1 (MP4 50388 kb)

Supplementary material 2 (MP4 37115 kb)

Supplementary material 3 (MP4 32685 kb)

Supplementary material 4 (MP4 59797 kb)


  1. 1.
    Schober K-U, Tannert T (2016) Hybrid connections for timber structures. Eur J Wood Wood Prod 74:369–377. CrossRefGoogle Scholar
  2. 2.
    Bainbridge R, Mettem C, Harvey K, Ansell M (2002) Bonded-in rod connections for timber structures: development of design methods and test observations. Int J Adhes Adhes 22:47–59. CrossRefGoogle Scholar
  3. 3.
    Feligioni L, Lavisci P, Duchanois G et al (2003) Influence of glue rheology and joint thickness on the strength of bonded-in rods. Holz Als Roh Werkst 61:281–287. CrossRefGoogle Scholar
  4. 4.
    Yeboah D, Taylor S, McPolin D et al (2011) Behaviour of joints with bonded-in steel bars loaded parallel to the grain of timber elements. Constr Build Mater 25:2312–2317. CrossRefGoogle Scholar
  5. 5.
    Steiger R, Gehri E, Widmann R (2007) Pull-out strength of axially loaded steel rods bonded in glulam parallel to the grain. Mater Struct 40:69–78CrossRefGoogle Scholar
  6. 6.
    Rossignon A, Espion B (2008) Experimental assessment of the pull-out strength of single rods bonded in glulam parallel to the grain. Eur J Wood Wood Prod 66:419–432CrossRefGoogle Scholar
  7. 7.
    Hunger F, Stepinac M, Rajčić V, van de Kuilen J-WG (2016) Pull–compression tests on glued-in metric thread rods parallel to grain in glulam and laminated veneer lumber of different timber species. Eur J Wood Wood Prod 74:379–391CrossRefGoogle Scholar
  8. 8.
    Stepinac M, Rajčić V, Hunger F, van de Kuilen JWG (2016) Glued-in rods in beech laminated veneer lumber. Eur J Wood Wood Prod 74:463–466. CrossRefGoogle Scholar
  9. 9.
    Tlustochowicz G, Serrano E, Steiger R (2011) State-of-the-art review on timber connections with glued-in steel rods. Mater Struct 44:997–1020. CrossRefGoogle Scholar
  10. 10.
    Steiger R, Serrano E, Stepinac M et al (2015) Strengthening of timber structures with glued-in rods. Constr Build Mater 97:90–105. CrossRefGoogle Scholar
  11. 11.
    Blass H, Laskewitz B (1999) Effect of spacing and edge distance on the axial strength of glued-in rods. In: Proceedings of the CIB-W18A Graz AustriaGoogle Scholar
  12. 12.
    Gonzalez E, Avez C, Tannert T (2016) Timber joints with multiple glued-in steel rods. J Adhes 92:635–651CrossRefGoogle Scholar
  13. 13.
    Dietsch P, Brandner R (2015) Self-tapping screws and threaded rods as reinforcement for structural timber elements: a state-of-the-art report. Constr Build Mater 97:78–89CrossRefGoogle Scholar
  14. 14.
    Charlotte Bengtsson, Carl-Johan Johansson (eds) (2002) Final report: GIROD—glued-in rods for timber structures. BoråsGoogle Scholar
  15. 15.
    Thelandersson S, Larsen HJ (2003) Timber engineering. Wiley, HobokenGoogle Scholar
  16. 16.
    Serrano E, Gustafsson PJ (2007) Fracture mechanics in timber engineering–Strength analyses of components and joints. Mater Struct 40:87–96CrossRefGoogle Scholar
  17. 17.
    Madhoushi M, Ansell MP (2017) Effect of glue-line thickness on pull-out behavior of glued-in GFRP rods in LVL: finite element analysis. Polym Test 62:196–202CrossRefGoogle Scholar
  18. 18.
    Broughton J, Hutchinson A (2001) Pull-out behaviour of steel rods bonded into timber. Mater Struct 34:100–109CrossRefGoogle Scholar
  19. 19.
    Andersen M, Høier M (2016) Glued-in rods in cross laminated timber. Master Thesis, Aarhus UniversityGoogle Scholar
  20. 20.
    Koets RJ (2012) Hoogbouw met cross laminated timber literatuur-, numeriek- en experimenteel (vervolg-) onderzoek naar CLT infilled frames. Master Thesis, Eindhoven University of TechnologyGoogle Scholar
  21. 21.
    Enders-Comber M (2015) Leistungsfähige Verbindungen des Ingenieurholzbaus. Doctoral Dissertaion, Karlsruher Institut für Technologie (KIT)Google Scholar
  22. 22.
    HILTI HIT-RE 500 V3: ultimate performance epoxy mortar for rebar connections and heavy anchoring. Accessed 29 May 2018
  23. 23.
    EN 14358:2016: Timber structures. Calculation and verification of characteristic values. European Committee for Standardization (CEN), BrusselsGoogle Scholar
  24. 24.
    Widmann R, Steiger R, Gehri E (2007) Pull-out strength of axially loaded steel rods bonded in glulam perpendicular to the grain. Mater Struct 40:827–838. CrossRefGoogle Scholar
  25. 25.
    NZW 14085 SC, New Zealand Timber Design Guide, Timber Industry Federation Inc., Wellington, New Zealand, 2007Google Scholar
  26. 26.
    Yeboah D, Taylor S, McPolin D, Gilfillan R (2013) Pull-out behaviour of axially loaded basalt fibre reinforced polymer (BFRP) rods bonded perpendicular to the grain of glulam elements. Constr Build Mater 38:962–969. CrossRefGoogle Scholar

Copyright information

© RILEM 2018

Authors and Affiliations

  1. 1.Section for Timber StructuresThe Slovenian National Building and Civil Engineering InstituteLjubljanaSlovenia
  2. 2.Division of Structural MechanicsLund UniversityLundSweden

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