Strength and slip factor of high strength bolted friction joints were obtained through loading tests. Specimens were assembled from weathering steel base members and blasted splicing members. Weathering steel plates were cut out from lower flange plate of a bridge that was exposed for 8 years in open inland field, and it has been generated protective rust on its surface. Base members were treated in some levels of rust removing. Applied treatments are blasting, disk sanding, powered wire brushing, manual wire brushing and cloth wiping. Protective rust decreases the slip factor, and thin crystalloid rust increases it, but thick rust over 100μm decreases it.
