By Japan Bridge Standard V, bridges must be installed aseismic strengthening systems for earthquake level II. Aseismic strengthening systems are representative connected to the main girder by high tension bolts. Bridges must be strengthened for transmitting the earthquake force smoothly and keeping their damage minimum. When we design strengthening structures. we meet with some difficulties. that are the installation means. joints of strengthening beams, a relation between earthquake force and strengthening structures. In the case of a box girder. such difficulties are remarkable because aseismic forces are large . In this paper. strengthening brakets and beams for a box girder of existing urban highway bridges are designed . then, FEM models are made up and FEM analysis results are discussed.
