抄録
The purpose of this paper is to elucidate the pull-out resistance mechanism of the lagscrewbolt joint embedded in parallel to the grain of glued laminated timber and to lead to the proposal of the design method. In this paper the state of stress and strain of lagscrewbolt joint is examined by numerical analysis because of difficulty of the experimental confirmation. Elastic analysis by FEM model was conducted and the results were compared with the experimental results. At the end, the pull-out resistance mechanism was clarified.
In general, Eq.(1) is used for the design of the lagscrewbolt joint. In the calculated values according to Eq.(1), the strength values are correlated to the embedment depth, and this tendency agrees with the experimental results. On the otherhand, regarding as the stiffness, the experimental results have low correlation with the embedment depth, but the calculated values are correlated to the embedment depth. Because, the stiffness between the calculated value by Eq.(1) and the experimental value is due to the difference in displacement evaluation method.
The stiffness was investigated by elastic analysis using FEM model. As a result, the following conclusions were obtained.
(1) FEM analysis by using the boundary zone stiffness of lagscrewbolt and timber in thin plate pull-out test are different from the experimental values. Because, the boundary zone conditions of thin plate pull-out test specimen perfectly reproduce the shear behavior of the interface of the joint.
(2) The stress state inside the timber can be confirmed by detailed FEM analysis calibrated by experimental results. From the lagscrewbolt stress of the FEM analysis result, stress at the boundary zone of lagscrewbolt and timber, stress of timber, and effective cross section “Aw” of timber were able to evaluated from Eq.(9) to Eq.(17). In addition, the coefficient “c” for finding the effective cross-sectional area of timber used in Eq.(4) was evaluated by Eq.(18).
(3) Comparing stiffness by the experimental values and FEM analysis and the simplified model, there is a different tendency only in the case of embedment depth is 200mm. This is considered to be due to the fact that the rate of damage caused by embedding lagscrewbolt is larger than the other embedment depth, so that variations in experimental values are large.
(4) The effective cross-sectional area of timber is highly correlated with the embedment depth. when the effective cross-sectional area of the timber exceeds a certain value, the stiffness does not become larger than a certain level.
