Large design loads are required for field splice of girder bridges with a thick and high-strength steel flange. A friction joint by high-strength bolts cannot be designed against such a case, because the capacity in usual size and arrangement of bolts is insufficient. This paper presents on the slip tests of high-strength bolted joints with filler plates inserted in the splice and base plates. Two kinds of filler plate used are low yield point steel and tungsten steel by thermal spray coating, which have different hardness. Test results of the relaxation in bolt tension force, the slip behavior of joints, the reduction of bolt force by loading and the slip resistance are discussed.
