Reliability Evaluation Of Failure Safety Cable In Bottom-Through Arch Bridge

The safety of suspender is a critical problem in the design of bottom-through arch bridge. The existing design theory of suspender is insufficient to consider the safety of cable breaking. Therefore, failure-safety cable is adopted to improve the safety of suspender. Failure-safety cable (FSC) system aims to locate such problems as the corrosion of the suspender in early period, etc. The earlier broken part of the suspenders plays a role of early alert. Meanwhile, the remian suspenders can still bear corresponding load to ensure the suspenders can not totally fracture, and they still have enough security after the fracture of some suspenders. The study of failure-safety cable of arch bridge not only has important theoretical significance, but possesses extensive project application prospect and great economic and social benefit.The basic theory of FSC and common element of FSC are intrduced firstlly. Genernally, F cable (Failure Cable) and S cable (Safety Cable) are included in failure-safety cable system. The stress of F cable is usually higher than that of S cable. Through optimizating such parameters of cable as angle, section area, prestressing stress, and so on, the tensile failure of F cable earlier than S cable is expected.Furthermore, the reliability theory and the first order reliability method (FORM) are introduced. The stochastic models of action effect and generalized resistance and limit carrying capacity are introduced in this thesis, which involve the stochastic effects of dead loads, vehical load, crowed load and parameters of material and geometric. To give a clear inspection about safety and reliability of FSC, the suspenders of Wu Xiang Ba Chi Jiang Bridge is investigated as an example. The reliability and safety factor are computed with different area ratio and stress ratio between F cable and S cable.Finally, the variation of safety factors and reliability indexes of F cable and S cable with different area ratio and differential stress is summarized. It indicates that the area of F cable should be less then 20 percent of whole section in Wu Xiang Ba Chi Jiang Bridge. In additional, the prestressing stress of F cable might be 700-900MPa higher than that of S cable. With the prementioned rational design of FSC, under the same service condition, F cable will break earlier than S cable, which plays a role of early alert. Meabwhile, S cable still can sustain load.