抄録
The calculation method for pull-out performance on lagscrewbolt (LSB) joint embedded in parallel to the grain of glued laminated timber is proposed in this paper. The shear stress distribution of the boundary zone between LSB and timber along LSB and material properties are separately considered in the formulae.
These formulae are derived by using the axial stress distribution along LSB which is calculated from the shear stress distribution function of the boundary zone along the LSB proposed in the past studies. These formulae are practical because they do not require any experimental efforts but only uses the given values such as specified design strength of materials that is defined in the notifications of MLIT.
The mechanisms of the yielding strength and the maximum strength of LSB joints are theoretically elucidated. The formulae to predict the yielding strength and the maximum strength which are derived based on these mechanisms are verified by numerical analyses.
It was found that the ductility of the boundary zone is strongly related to the ratio of the yielding strength to the maximum strength. When the ductility of the boundary zone is poor, the yielding strength is equal to the maximum strength. When the ductility is sufficient, the maximum strength is reached when the boundary zone in all area yields. These tendencies were confirmed by numerical analysis.
In the past studies, the pull-out elastic stiffness obtained from experiments disagreed with the calculation results because of different definitions of the pull-out displacement of LSB joint between the experiment and calculation.
In this paper, the relative displacement between the position of the timber at the tip of LSB and the position of the root of LSB is defined as the pull-out displacement of the LSB joints. According to this definition, it is confirmed by numerical analyses that the pull-out elastic deformation of the LSB joint is the total value of the elongation along LSB and the shear deformation of the boundary zone at the position of the tip of LSB.
The formulae derived here were verified by the pull-out test which was conducted under different types of LSB, wood species and embedment lengths.
