Analytical Study on Safety Level of Stay Cables of Cable-stayed Bridge and Extradosed Bridge under Fatigue and Ultimate Limit States

Cable-stayed bridges and extradosed bridges are thought to be similar kinds of structures because both bridges use stay cables for reinforcement. However, the safety factors of stay cables of both bridge types are stipulated differently in many international standards i.e. Japanese specifications suggest the safety factors of 2.5 and 1.67 for the design of cable-stayed bridges and extradosed bridges respectively. In this paper, an analytical study is carried out for the investigation of the safety level of stay cables of both bridge types at fatigue and ultimate limit states. Subsequently, the Mean Value First Order Second Moment (MVFOSM) reliability method is also performed for the verification of safety factors of stay cables. Finally, it is found that the safety factors of stay cables in the range of 2.3 to 2.5 and 1.67 are essential to satisfy the fatigue and ultimate limit states and target reliability index of 4.0 of cable-stayed bridges and extradosed bridges respectively.