The dynamic responses of a steel deck tension-tied arch bridge subjected to earthquake excitations were investigated. The 189 m (620 ft) Birmingham Bridge located in Pittsburgh, PA was selected as an analytical model for the study. Two analytical models were considered for representing the bridge deck system: in one of the bridge deck was replaced by a series of simple beams connected to the tension-ties at panel points; in the other the deck was modeled by using substructures. To evaluate the seismic resistance of the bridge, a comparative study has been conducted. Three orthogonal records of the El Centro 1940 earthquake were used as support excitation for the seismic response analysis. Based on the study, it was found that the simple beam model would be inadequate for representing the bridge deck system in the seismic response analysis of the bridge. Additional study results are discussed.