There are some examples of studies focused on the slip coefficients in high-strength bolted frictional joints with various holes. It found that the slip coefficients in the joints with oversized holes and slotted holes were less than the coefficients in the joints with normal holes. However, in Japan, there is no rule regarding the slotted holes, and the use is not accepted. In this study, FEM was carried out and the mechanism by which the slip coefficients were decreased was investigated in the joints with slotted holes and oversized holes varied the slip/yield resistance ratio and the washer thickness. Therefore, the mechanism of the slip coefficient reduction is clarified.
