Fatigue life assessment of Bosphorus Bridge hanger cables

The Bosphorus Bridge, constructed in 1973, is an iconic suspension bridge located in the heart of Istanbul, Turkey serving as an extremely important link of the city transportation network with an average daily traffic of around 190,000 vehicle/day. Recently, the bridge has undergone a major retrofit work which also included replacement of the entire suspender system by changing the inclined orientation of the hangers to vertical. The hanger cables of a suspension bridge are susceptible to fatigue failures under fluctuating traffic loads and wire breaks in cables is a common problem which may also result in replacement of them. This study aims to evaluate the fatigue performance of the newly installed hanger cables under traffic loads. For an existing bridge, it is a meaningful concern for bridge operators as well in terms of asset management and in order to meet the increasing traffic demands through out the years of service. A detailed 3D finite element model of the bridge is developed and the model is verified by using the ambient vibration measurements taken from the bridge. A realistic traffic time history loading scenario is generated by simulating the traffic flow. The resulting stress time histories of the hanger cables are obtained from the analytical model. Fatigue analysis and life prediction of hanger cables under variable amplitude stress history due to traffic loading is performed using a S-N curve based on test results. The factors contributing the damage level such as hanger length and vehicle types are discussed Also, the effect of corrosion on fatigue life is taken into account.