A thesis is presented on the seismic evaluation of a viaduct using non-linear analysis techniques. The Bolu viaduct is a 2-3 km long seismically isolated structure with two parallel bridges each with a span length of 39.2 m and pier height of maximum 49 m that was nearly complete when it was struck by the 1999 Duzce earthquake in Turkey. With the design based on AASHTO standards, it suffered complete failure of the seismic isolation system and narrowly avoided total collapse due to excessive superstructure moment. After investigations the retrofit of the viaduct had been decided due to the study carried out by Michele Calvi and J. Nigel Priestley. This thesis concentrates on the retrofitted structure of Viaduct 1 by non-linear time history analysis.