Abstract. In this paper, a numerical approach to the reliability analysis of prestressed reinforced
concrete long span bridges is presented. A bridge is modeled by nite element software and the analysis
is performed in time domain by considering the bridge material nonlinearity. The considered random
variables are: Specic strength of concrete, yield stress of steel bars, yield stress of prestressed bars,
all sectional dimensions, structural damping ratio, eective depth of steel bars and the magnitude and
PGA of earthquake. In this study, the reliability of a bridge structure is evaluated under earthquake
excitations. For this purpose, the First-Order Second-Moment (FOSM) method is used. In this method,
the mean value and standard deviation of the random variables are considered for evaluating structural
reliability. The proposed procedure is applied to evaluate the reliability of an existing prestressed arch
concrete bridge located in Bandar-e-Anzali in Iran. Bandar-e-Anzali is a very high-risk earthquake zone.
The results of the study show that the structural damping ratio, magnitude and PGA of earthquakes have
a signicant eect on the variation of reliability in the structure, while variations in the dimensions of
the structure have little eect on the reliability index.