This study was aimed at evaluating and estimating the shear strength properties of nailed wood (Sugi) connection damaged by decay. Steel and stainless steel nails were driven into specimens, and then the specimens were decayed by compulsion using cultured brown rot fungi (Fomitopsis palustris). The Pilodyn’s penetration depth and the bearing strength were measured to estimate the shear strength of nailed connection damaged by decay. The single shear tests of nailed connection were conducted to investigate relationship between Pilodyn’s penetration depth and shear strength. It was found that the stainless steel nails slightly decreased yield strength with increasing penetration depth. However, the steel nails showed an opposite tendency due to rust. The deeper the penetration depth caused the lower the bearing strength. The shear strength of decayed nailed joint was also compared with the estimated strength by the European Yield Theory (EYT) based on the bearing strength calculated from the penetration depth, and as results of both data showed good agreement. Thus, it was proposed 29 mm of Pilodyn’s penetration depth as the threshold value for nailed connection using Sugi.
