Force distribution in self-tapping screws: experimental investigations with fibre Bragg grating measurement screws

Abstract

The pull-out resistance of fully threaded, self-tapping screws under axial loading has been investigated intensively in the past. Actual design models are based mainly on empirical data because the detailed interaction between the screw thread and the surrounding timber member remains unclear and might depend on the test set-up. An innovative screw sensor with 19 internal fibre Bragg gratings (FBGs) was developed to measure the forces along the screw axis. The screw diameter was 12 mm and the maximum embedding length was 360 mm. The FBG measurement screw was applied in pull-out tests under different support conditions. The results carried out show details of the axial forces along fully threaded screws depending on the magnitude of the screw axis to grain angle, the embedding length, the material and the support conditions. Load transfer between the screw and the surrounding timber was determined by means of the change of axial forces along the screw axis. A comparison of the experimental results with Volkersen’s theory points out the decisive dependency of the support conditions on the axial forces in fully threaded self-tapping screws. Additionally, the experimental test results show indications of shear and compressive stresses in the interface of the measurement screw.

Numerical assessment of the interaction between shear and moment actions in LVL bolted connections

“…The screws were modelled using 2 node beam elements with 6 degrees of freedom (DOFs) at each node. While for screws used in perpendicular to grain direction, a linear elastic bonded contact with timber might be accepted [37], in this study the screw was joined to the timber through a spring element connecting the pullout DOF of co-located nodes of timber and the screw. The spring constitutive model is shown in Fig.…”

Fibre-Optic Measurements for Monitoring Adhesively Bonded Composite Beams

“…In the field of timber structures, a comparable measurement method, so-called Fibre Bragg Grating (FBG), was used by Claus et al [5] to investigate the force 1 Jens Frohnmüller, University of Kassel, Timber Structures and Building Rehabilitation, Germany, jens.frohnmueller@uni-kassel.de 2 Werner Seim, University of Kassel, Timber Structures and Building Rehabilitation, Germany.…”