Abstract: The Ohnaruto Bridge, one of the Honshu-Shikoku Bridges in Japan, is a three-span two-hinged stiffening-truss suspension bridge. Multi-column foundations were adopted for the towers. In the original seismic design of the Ohnaruto Bridge, an inland near-field earthquake was not considered for the design seismic force. In order to grasp the seismic performance, seismic performance verification was conducted, which concluded that the seismic capacity of the multi-column foundations was not sufficient. Steel pipes had been used as concrete formwork for the construction of the columns and they were left as protective member of the columns. Based on the seismic verification, it was concluded that the seismic capacity could be achieved if the steel pipes were considered as structural members. Therefore, corrosion protection of steel pipes has been carried out to keep the pipes in good condition and ensure they continue to serve this purpose.