In order to improve durability of corrosion, previous studies reported that countersunk head bolts can be applied to high strength bolted friction grip joints. The surface treatment of the countersunk hole is specified to be inorganic zinc rich paint, if blasting of countersunk hole can be omitted in the construction site, the workability will improve. In this research, slipping test was carried out to evaluate the effect of surface treatment without blasting of countersunk hole on slip strength of friction grip joints with high strength countersunk head bolts. As a result, the effect of surface treatment of countersunk hole on slip strength is very small.
