In case of deciding whether a bridge should be replaced or enhanced its service life, it is important
to evaluate the seismic resistance performance of the foundation because of huge amount of expense
for its retrofitting. However, verification and modeling method of timber piles subjected to the earthquake are
not specified in current Japanese Specifications for Highway Bridges [Japan Road Association, 2004], seismic
resistance of the timber pile foundation is not clear as well as that of intact state. Osaka city has about 100
bridges supported by timber pile foundation, it is severely necessary to clarify the seismic resistance performance
of it. This paper presents the experimental and analytical investigation conducted by authors, in order to
evaluate the structural health of an aged timber pile and its seismic resistance performance under the strong
earthquake.