【正文】 ples. The impact effect of the remaining ponents of the arch bridge due to the breakage of one or more suspenders is obtained by appropriate simulation using the prehensive mercial software ANSYS. It can be concluded from the analysis in this paper that the new way to design the suspenders for the through and halfthrough arch bridges can assure the safety of the bridge effectively even though one or more suspenders happen to break. 2 INTRODUCTION With the rapid development of new materials and construction technologies, the modern arch bridges are now entering a new era. The span length of the modern arch bridges is increasing,and the first two longest modern arch bridges are the Enchainment Yangtze River Bridge and the Lu Pu bridge, respectively. The Enchainment Yangtze River Bridge built in 2021 is a tied steel truss arch bridge with a span length of 552m。 ., E1=E2, A1=A2and θ 1=θ 2, where E, A and θ are the elastic modulus, cross section area and inclined angles of the suspender, respectively. That means they have the same or similar stress and variation of stress in service. They are also under the same or similar corrosion environment since they are located at the same anchorage. Hereby, it can be concluded that the two suspenders at the same anchorage will fail at the same or similar time because of the almost equal level of both fatigue load and corrosion on the discussion above, it can be seen that the doublesuspender system designed in the traditional way will not improve both the safety of the arch bridge and the convenience of suspenders replacement pared to the singlesuspender system. 4 A NEW WAY TO DESIGN ARCH BRIDGE SUSPENDERS In order to keep the remaining structure of arch bridge still safe when one suspender happens to break, the doublesuspenders must be designed with different service life. The only way to achieve this aim is to design the two suspenders at the same anchorage with different either material or cross section areas since they carry the same fatigue loads and are under the same corrosion the two suspenders at the same anchorage are designed with different materials, the extra in convenience both in design and construction of the arch bridge will be induced. The better way is to make the two suspenders with different cross section areas A Fand AS()respectively. With different cross section areas, the two suspenders at the same anchorage will have different stress levels and variation of stresses, that is to say, there are σ F,max≠σ S,max, σ F,a≠σ F,a. Σ max and σ a are the maximum stress and amplitude of the stress of the suspenders,respectively. Based on the basic theories of the material fatigue, the material or member has different service lives with different maximum stress and stress amplitude. Figure 2 : Doublesuspender anchorage designed in new way : (a) Parallel doublesuspender anchorage,(b) Inclined doublesuspender anchorage Thereupon, the two suspenders at the same anchorage may have different service lives if they are appropriately designed with different cross section areas even though they are made of the same material and under the same fatigue loads and corrosion environment. During the service life of the arch bridge, the suspender with the larger cross section will still keep the arch bridge safe when the suspender with the smaller cross section at the same anchorage happens to reasonability and reliability of this new way to consider the suspender design will be proved by numerical parison study on a troughtype modern arch bridge, Sazhen North Railway Station Bridge, using prehensive mercial software ANSYS in the following section in this paper. 5 NUMERICAL ANALYSIS EXAMPLE Description of Sazhen North Railway Station Bridge Sazhen North Railway Station Bridge with a span length of 150m is a throughtype modern concretefilled steel tubular arch bridge. It was built in 2021 and located at the Sazhen North Railway Station, spanning all railways at that station. Risetospan ratio of this bridge is 1/ elevation view of the bridge is shown in . The width of the general bridge deck except at the end of the arch ribs with a bridge deck width of 28m. Horizontal cables in the steel box girders of the bridge deck are adopted to balance the horizontal force of the arch ribs. This bridge has two vertical arch ribs and each arch rib is posed of four concretefilled steel tubes and thus has a truss cross section of in width and in height. The material properties of the bridge are listed in Table 1. The more details about this bridge is found in Li eta. (2021). Finite element model of the example bridge A detailed finite element model () of the example bridge was developed using the prehensive mercial software ANSYS. In this 3 dimensional (3D) finite element model,every ponent is appropriately modeled. As mentioned above, each arch rib is posed of four concretefilled steel tubes. These concretefilled steel tubes are modeled by BEAM4 element. Since the concretefilled steel tube is a posite member, the equivalent cross sectional properties and material properties are obtained first by editing an APDL file based on some equivalence rules, and then assign these equivalent cross sectional properties and material properties to the corresponding beam elements. The equivalent cross sectional properties and material properties of the concretefilled steel tubes are listed in Table 2. The BEAM4 element is also adopted to model the arch rib bracings, the longitudinal steel box girders, the steel tubes connecting the four concretefilled steel tubes of the arch rib. The