Carried out dynamic analysis as a countermeasure for a large earthquake, stress of some main members in a steel truss bridge are exceeded these yield stress. We make these members reinforced by using bolted cover plates to improve member resistance. However, regarding this reinforcement, it is not clearly regulated. And the mechanism of stress transfer of the reinforcement using a bypass device especially under the tensile load is not obvious enough. Therefore, assuming design conditions for such as required numbers of bolts to transfer stresses between base plate, cover plate and bypass device, FEM analysis by using models designed these conditions is carried out by noticing load conditions and some structural forms of bypass device. It is concluded that the mechanism of stress transfer is obvious.
