Timber joints with modified bonded-in rods and concrete-type adhesives

Investigations on the bonding behavior and pull-out strength of mechanical fasteners casted in Douglas fir (Pseudotsuga menziesii)

Connections based on glued-in rods have been reviewed and further developed to increase the pull-out strength parallel to grain and overcome restrictions when it comes to bonding on site. The adhesive bond between threaded rod and rectangular sawn wood and roundwood was achieved by further developed concrete-type adhesives (CTA) with much thicker bondline, compared to standardized glued‑in rods. The new-type joint has been investigated on Douglas fir specimens to assess the characteristic and design capacity under different climate and service conditions and to describe the influence of moisture induced damage and wood defects on the connection capacity and the slip modulus.

Objectives

  • Assessment of the structural behavior of modified bonded-in rods under different service conditions,
  • Assessment of crack propagation, moisture induced damage and wood defect influence on the connection capacity,
  • Assessment of the characteristic (5%-fractile) and design values of the single fastener capacity (experimental and analytical),
  • Assessment of the overall connection stiffness and capacity.

Methods

  • Capturing of the natural crack and annual ring pattern of each specimen,
  • Visual grading to determine strength classes according to EN 1912,
  • Specimen preparation in three test series,
  • Pull-out testing after seven days of adhesive hardening under indoor lab conditions (service class 1 conditions) and 1,100d climate exposure (SC 2 and SC 3 conditions),
  • 2D and 3D optical measurement of the surface displacement with subsequent numerical calculation of the corresponding strain field and evaluation of the climate impact on the specimen and joint capacity,
  • Investigations on the crack propagation in the CTA and the influence on the effective embedment length and capacity,
  • Investigations on the influence of natural cracks in wood on the joint capacity,
  • Calculation of the design capacity from testing according to Eurocode and comparison with the capacity of glued-in rods according to Eurocode 5, German National Annex

Stats

Research team:

M. Sc. Leonhard Lieyanto, M. Sc. Tarick Chahade, M. Eng. Leif Schmidt, M. Eng. Verena Ubl, M. Eng. Philipp Schäfer, Prof. Dr. Kay-Uwe Schober (1)
Dipl.-Ing. (FH) Jan Weber, Prof. Dr. techn. Wieland Becker (2)

(1)  Hochschule Mainz, Forschungsgruppe Holz und Kunststoffe
(2)  Holzkompetenzzentrum Trier

Duration:     March 2016 – October 2019
Budget:        190,000 €
Contact:       Prof. Dr. Kay-Uwe Schober

Parts of the research were funded by the Rineland-Palatinate Ministry of Science, Further Education and Culture. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the funding agency.