PROPOSAL OF CALCULATION FORMULA FOR PULL-OUT STRENGTH OF GLUED-IN ROD JOINT

Abstract

 In recent years, the construction of medium- to large-scale buildings with timber structures is being promoted enthusiastically around the world from the perspective of global environment issues. However, in terms of the structure, as the scale of the building increases, the stress on the joints also increases, presenting the need for joints with high strength and rigidity. This issue has long been a concern in the field of timber structures. Based on these circumstances, the authors decided to focus on glued-in rod joint. Currently, since a formula to calculate the pull-out strength of glued-in rod has not been established, experiments are required to determine the pull-out strength and pull-out rigidity before actual use.

 This paper contains the following research objectives. A formula to calculate the pull-out strength is proposed by improving the formula of Johansson, Gustafsson, et al. to model a glued-in rod with an adhesive layer that has a round thickness using the Volkersen model. Furthermore, the pull-out strength is clarified through pull-out test of the glued-in rod joint with embedment length (25mm~800mm), base material cross section, adhesive type, and rod diameter as the parameters, in order to verify the results against the proposed formula to shed light on its applicability. In addition, the properties of the impact that each parameter in the proposed formula has on pull-out strength are clarified.

 The insights that became clear through pull-out test of glued-in rod joint and verification of the proposed formula for calculating pull-out strength are as follows. A calculation formula for pull-out strength was derived by devising a model for glued-in rod inserted with an adhesive layer that has a round thickness using the Volkersen model. The relationship between pull-out strength, the average shear stress at the wood boundary per unit of adhesion area when under maximum proof stress, and embedment length was clarified through pull-out test of the glued-in rod joint. By comparing the values from the experiment with the pull-out strength from the proposal formula, it was confirmed that the proposal formula can be recreated with good precision. Its applicability was proven. The parameters for the formula were studied to clarify how each variable in the formula affect pull-out strength and the average shear stress at the wood boundary per unit of adhesion area when under maximum proof stress. To be specific, the smaller the modulus of rigidity of the adhesive layer, the greater the pull-out strength, and the deeper the embedment length, the more significant the impact.

 Future tasks include the proposal of a formula to calculate pull-out rigidity in addition to pull-out strength and verification of the input values when using the calculation for design.