In this paper, we studied on the method of seismic reinforcing the gusset plate joint in the existing upper steel arch bridge. Because the bracing member and joints of arch bridges constructed in the past are designed only with seismic force by a level 1 earthquake motion, by a level 2 earthquake motion the bracing member is not only damaged but also the gusset plate joint is damaged. Therefore, we conducted experiments on the panel including bracing members and the joints using 1/2 scale specimens of actual bridges, we made clear the ultimate behavior of the bracing member and the joint designed by level 1 earthquake motion. Furthermore, we proposed a method for reinforcing the joint, and confirmed the effectiveness of the method by experiments using 1/2 scale specimens and FEM analysis.
