More than 40% of the bridges in conventional Korean railway lines are track-on steel-plate-girder (TOSPG)
bridges. They are characterized by a superstructure consisting of railway tracks sitting directly on steel
plate girders without any ballast system. Most of these bridges have been designed with little or no
consideration given to seiic loading. In this paper, seiic fragility curves of TOSPG bridges in Korea
are developed. Fragility curves are developed first for the components, by using the probabilistic seiic
demandmodel. The developed component fragility curves showthat the bearings are themost vulnerable
components of the TOSPG bridges against seiic loading. On the other hand, the piers are much less
vulnerable, although they contain no reinforcing bars. This is because the superstructure mass is very
light, and therefore horizontal loading transferred from the superstructure to the piers is minimal. A
generic damage measure is introduced for measuring the system-level damage of structures out of the
component-level damages. The system fragility curves are then developed, using the generic damage
measure. Finally, representation of seiic risk in terms of expected seiic losses is demonstrated. This
demonstration shows how the fragility ysis is utilized for risk assesent and support in decision-
making.
