Reliability Assessment of the Urumia Lake Bridge Considering the Failure due to the Fatigue damage

Steel bridges structures are subjected to repeated cyclic stresses due to traffic load. The damage accumulation of these cyclic stresses can initiate cracks in a members leading to fatigue failure. The randomness of the nature of vehicle-induced fatigue load in combination of fatigue strength may cause to increase uncertainty in the prediction of the bridge fatigue life. In this research, the fatigue detail coefficient A, and the equivalent stress range ,􀀁􀀂􀀃 , are assumed as random variables and then according to specified fatigue limit state function reliability the index, 􀀄 , is calculated. This approach has been applied to the Urumia lake bridge and results show that the lognormal probability distribution function can be used effectively to specify uncertainty in the stress range. Also, the fatigue reliability index decreases b increasing the service life of the Urumia lak bridge.