【文章內(nèi)容簡介】 ends of the two box girders are summarized in Table 4. There are two arch ribs in Sazhen North Railway Station Bridge and 17 doublesuspenders are anchored in each arch rib. For the convenience of the following analysis, the anchorages of each arch rib are numbered from 1 to 17 from west to east。 the two suspenders at each anchorage are numbered as a and b for north arch rib, a’ and b’ for south arch rib, is to say, the 34 suspenders in the north arch rib are marked as 1a, 1b, 2a, 2b, … , 17a, and17b respectively。 accordingly, those 34 suspenders in the south arch rib are 1a’ , 1b’ , 2a’ ,2b’ , … , 17a’ , and 17b’ () . Impact effect study due to the suspender break When one or more suspenders break, there will be impact effect on the remaining structure and its other ponents. It is very important to know well the impact effect. In this section, the break of a suspender is appropriately simulated by assuming that two forces with equal value but opposite directions applied respectively to the broken suspender’ s anchorages on arch riband bridge deck decrease to 0 within a time slot δ t from the axial force value of that impact effect due to a suspender’s break on the other ponents of the bridge is studied by carrying out timehistory analysis based on the 3D finite element model in ANSYS. Of course, the impact effect due to a suspender’ s break on the other ponents of the bridge is closely related to the time slot δ t and the structural properties of the bridge. For a bridge in service, the impact effect is mainly dependent on the value of the time slot δ t. Here the impact coefficient η is defined as the ratio of the structural response under both the impact and deal loads to that only under the deal loads. The structural response of the bridge under kinds of loads refer to the stress, bending moment, axial force, displacement, and so on. In order to determine the appropriate value of the suspender break time slot δ t for the following analysis, the relationship between the impact coefficient η and the suspender breaktime slot δ tis studied based on different suspender break cases. Theoretically, when a suspender(a or a’ ) breaks, the other suspender (b or b’ ) at the same anchorage should be impacted mor strongly than other members of the bridge, such as bridge deck, arch rib, and so on. Because of the symmetric arrangement of the suspenders () in Sazhen North Railway Station Bridge, the suspenders anchored to anchorage 1 to 9 are chosen to carry out the break simulation and impact effect analysis. At each anchorage, assuming the a (or b) suspender breaks, the curve to represent the relationship between the impact coefficient η of the corresponding b (or a) suspender’ stress and the time slot δ tare obtained after the timehistory analysis in ANSYS. The η δ t curves of four suspender break cases are plotted in , shortest suspender 1a, second shortest suspender 1b, medium length suspender 5a and longest suspender9a. From , it can be seen that relatively larger variation of η happens when the value of the time slot δ tin the range of (, ) . When the suspender break time δ tis longer than ,the impact effect is small and varies little with the increment of the break time. When the suspender break time δ tis shorter than , the impact effect is obvious but varies little with the variation of the break time. So the impact effect due to the suspender break can be appropriately simulated and obtained by the timehistory analysis if the break time slot δ t assumed to be shorted than . In the following analysis, the time slot δ tis taken as the value of . It can also be shown in that the impact effect induced by the shorter suspender’s break is larger than that by the longer one. Analysis on the present design In the present design of the example bridge, every suspender is posed of 61 Φ 7mm parallel prestressed steel wires. The characteristic tension strength of the steel wires is 1670MPa. In this section, the safety of the remaining structure of the example bridge is studied in various cases assuming that different numbers of suspenders at different anchorages happen to break. Theoretically speaking, the two suspenders at the same anchorage should break at the same time since they are designed with the same material and cross section. When two suspenders at the same anchorage happen to break at the same time, the other suspenders, bridge deck,transverse girder and longitudinal girder close to that anchorage will break in succession. For example, when the suspenders 2a and 2b break at the same time, the suspenders 1a, 1b, 3a and3b will break successively, the concrete plate and the longitudinal steel box girder near to the anchorage 2 will break, too (). When the suspenders 7a and 7b break at the same time, the suspenders 6a, 6b, the concrete plate and the longitudinal steel box girder near to the anchorage 6 will fail successively (). Analysis on new design Based on the new way put forward in this paper, the two suspenders at a same anchorage are hereby designed differently, one as 137Φ 5 prestressed steel wire strand, the other 207Φ 5prestressed steel wire strand. The suspenders 1a to 17a and 1b’ to 17b’ are assigned with137Φ 5 prestressed steel wire strand, 1b to 17b and 1a’ to 17a’ with 207Φ 5 prestressed steel wire strand. The characteristic tension strength of the prestressed steel wire strand is allowable stresses of the steel wire stand are 744MPa and 930MPa, respectively for temporary and permanent situation. Two representative cases are studied, (1) the suspender 1a posed of 13