外文翻譯--大跨度斜拉橋的力學(xué)性能（原文）

1、30 / JOURNAL OF BRIDGE ENGINEERING / FEBRUARY 1999ULTIMATE BEHAVIOR OF LONG-SPAN CABLE-STAYED BRIDGESBy Wei-Xin Ren1ABSTRACT: The study described here investigates the nonlinear static and ultimate behavior of a long-spa

2、n cable-stayed bridge up to failure and evaluates the overall safety of the bridge. Both geometric and material nonlinearities are involved in the analysis. The geometric nonlinearities come from the cable sag effect, ax

3、ial force-bending interaction effect, and large displacement effect. Material nonlinearities arise when one or more bridge elements exceed their individual elastic limits. The example bridge is a long-span cable-stayed b

4、ridge of a 605 m central span length with steel box girder and reinforced concrete towers under construction in China. Based on the limit point instability concept, the ultimate load-carrying capacity analysis is done st

5、arting from the deformed equilibrium configuration due to bridge dead loads. The effects of the steel girder hardening and the girder support conditions on the ultimate load-carrying capacity of the bridge have been stud

6、ied. The results show that the geometric nonlinearity has a much smaller effect on the bridge behavior than material nonlinearity. The overall safety of a long-span cable-stayed bridge depends primarily on the material n

7、onlinear behavior of individual bridge elements. The critical load analysis based on the bifurcation point instability concept greatly overestimated the safety factor of the bridge. The ultimate load-carrying capacity an

8、alysis and overall safety evaluation of a long-span cable-stayed bridge should be based on the limit point instability concept and must trace the load-deformation path of the bridge from applied loads to failure.INTRODUC

9、TIONModern cable-stayed bridges have been experiencing a re- vival since the mid-1950s, although the concept of supporting a bridge girder by inclined tension stays can be traced back to the seventh century (Podolny and

10、Fleming 1972). The increas- ing popularity of contemporary cable-stayed bridges among bridge engineers can be attributed to: (1) the appealing aes- thetics; (2) the full and efficient utilization of structural ma- terial

11、s; (3) the increased stiffness over suspension bridges; (4) the efficient and fast mode of construction; and (5) the rela- tively small size of the bridge elements. Over the past 40 years, rapid developments have been ma

12、de on long-span cable-stayed bridges. Cable-stayed bridges are now entering a new era, reaching central span lengths of from 400 to 1,000 m and even longer. With the increasing central span length of modern cable-stayed

13、bridges, the trend of the bridge is to use more shallow and slender stiffening girders to meet the requirements of aerodynamics. In this case, bridge safety (strength, stiffness, and stability) under service loadings and

14、 environmental dynamic loadings (such as impacts, winds, and earthquakes) presents increasingly important concerns in both design and construction. A long-span cable-stayed bridge exhibits nonlinear charac- teristics und

15、er loadings. It is well known that these long-span cable-supported structures are composed of complex structural components with high geometric nonlinearities.? The nonlinear axial force-elongation behavior for the in- c

16、lined cable stays under different tension load levels due to the sag initiated by their own weight (sag effect). ? The combined axial load and bending moment interaction for the girder and towers. ? Large displacement, w

17、hich is produced by the geometry changes of the structure.In addition, nonlinear stress-strain behavior of each bridge1Prof. and Head, Div. of Bridge and Struct. Engrg., Dept. of Civ. Engrg., Changsha Railway Univ., Chan

18、gsha, 410075, People’s Republic of China. Note. Discussion open until July 1, 1999. To extend the closing date one month, a written request must be filed with the ASCE Manager of Journals. The manuscript for this paper w

19、as submitted for review and possible publication on June 19, 1997. This paper is part of the Journal of Bridge Engineering, Vol. 4, No. 1, February, 1999. ?ASCE, ISSN 1084-0702/99/0001-0030–0037/$8.00 ? $.50 per page. Pa

20、per No. 16039.element (including yielding) should be included in the ultimate load-carrying capacity analysis and overall safety evaluation. Many investigators have presented different analysis meth- ods to deal with thi

21、s highly nonlinear structure (e.g., Baron and Venkatesan 1971; Tang 1976; Como 1985). Some re- searchers disregarded all sources of nonlinearities (e.g., Krishna et al. 1985) whereas others included one or more of these

22、sources. Most nonlinear analyses of cable-stayed bridges have focused on plane (Fleming 1979) or space (Nazmy and Abdel-Ghaffar 1990a; Kanok-Nukulchai and Guan 1993; Boonyapinyo et al. 1994) geometric nonlinear behavior.

23、 But some analysis (Nakai et al. 1985; Seif and Dilger 1990) in- volved both geometric and material nonlinearities and revealed that the material nonlinearity was dominant in the nonlinear static behavior of long-span ca

24、ble-stayed bridges. It is partic- ularly true for long-span segmental concrete cable-stayed bridges. Indeed, the ultimate load-carrying capacity of cable-stayed bridges is generally dependent on the stability conditions

25、in- volved in both elastic-plasticity and large deformations. With the ever-increasing application of the limit state design method in the structural design instead of the allowable stress method, understanding and study

26、ing on the overall ultimate behavior of long-span cable-stayed bridges becomes essential. Based on the limit point instability concept, the present study investi- gates the nonlinear static and ultimate behavior of a lon

27、g-span cable-stayed bridge under the completed bridge state. Both geometric and material nonlinearities are included in the anal- ysis. Parameters such as the steel girder material hardening and the girder support condit

28、ions are studied in this paper. All analyses start from the deformed equilibrium configuration due to bridge dead loads. The main objective is to achieve a syn- thetic understanding of the static ultimate behavior and to

29、 eval- uate the overall safety of a long-span cable-stayed bridge.NONLINEAR CONSIDERATIONS AND SAFETY EVALUATIONNonlinear Considerations in AnalysisA cable-stayed bridge is a nonlinear structural system in which the gird

30、er is supported elastically at points along its length by inclined cable stays. Although the behavior of the material is linearly elastic, the overall load-displacement re- sponse may be nonlinear under normal design loa

31、ds (e.g., Fleming 1979; Nazmy and Abdel-Ghaffar 1990a). Geometric nonlinearities arise from the geometry changes that take place32 / JOURNAL OF BRIDGE ENGINEERING / FEBRUARY 1999FIG. 1. Elevation of Example BridgePcritic

32、al v = (3) PexistingThe lowest safety factor of his example cable-stayed bridges was 9.97. Boonyapinyo et al. (1994) studied the geometric nonlinear instability of long-span cable-stayed bridges also based on the bifurca

33、tion point instability concept. In their analysis, all geometric nonlinear sources as mentioned above were consid- ered, but the material nonlinearity was not included. Their ex- ample bridge was a long-span cable-stayed

34、 bridge with the center span length of 1,000 m. The buckling factors of the bridge were given. Therefore, a cable-stayed bridge is no longer a perfect struc- tural system because? Its elements such as the girder and towe

35、rs are the mem- bers subjected to both axial forces and bending moments. ? Before the live loads are applied, the bridge has sustained heavy dead loads and built-in construction loads so that initial deformations and str

36、esses exist in every member.Obviously, the concept of bifurcation point instability based on the eigenvalue analysis will be invalid for cable-stayed bridges. The critical load analysis of cable-stayed bridges should be

37、the limit point instability problem. Another important feature is the material nonlinearity. Ac- tually, before the applied load is far less than the critical load based on the bifurcation point instability concept, the

38、stresses in some members might have exceeded the material yielding limit and the bridge has already failed. Nakai et al. (1985) studied the ultimate load of a cable-stayed bridge with a 355 m central span length based on

39、 elastic-plastic and finite dis- placement analysis. They showed that the ratio of ultimate load to design load was about 3.0. Seif and Dilger (1990) studied the ultimate loads of a prestressed concrete (P/C) cable-staye

40、d bridge. Their results for an example bridge showed that the maximum ratio of live load to dead load was about 2.8. All of these values are much lower than those using Tang’s for- mulas based on the bifurcation point in

41、stability analysis. Hence, the bifurcation point instability critical load of cable- stayed bridges greatly overestimates the load-carrying capacity of the bridge, which is not conservative for the safety evalu- ation of

42、 cable-stayed bridges. The ultimate load-carrying ca- pacity of long-span cable-stayed bridges based on the limit point instability concept should be studied sufficiently to eval- uate the overall safety under both desig

43、n and construction. However, the ultimate load-carrying capacity of a cable- stayed bridge at the limit point is not easily obtained. The ultimate load-carrying capacity analysis should involve both geometric and materia

44、l nonlinearity. There is no closed-form solution and a numerical method becomes necessary. The ul- timate load-carrying capacity of a cable-stayed bridge can only be obtained throughout the load-displacement curves from

45、ap- plied loads to failure. Presently, the ultimate load-carrying capacity of structures has become increasingly attractive because of the application of the limit state design method. It is well known that thestructure

46、should be designed for sufficient ultimate load-car- rying capacity; therefore, determining the ultimate load-car- rying capacity of the structure is of utmost importance. If the ultimate load-carrying capacity of a long

47、-span cable- stayed bridge has been determined, the overall safety factor n of the bridge can be written byqu n = (4) q0where q0 is the design load of the bridge; and qu is the ultimate load. Both include dead loads and

48、live loads.DESCRIPTION OF EXAMPLE LONG-SPAN CABLE-STAYED BRIDGEThe example bridge studied here is the Ming River long- span cable-stayed bridge, with a 605 m central span length, which is now one of the longest central s

49、pan cable-stayed bridges under construction in China. The bridge span arrange- ments are (90 ? 200 ? 605 ? 200 ? 90) m. There are four traffic lanes. The elevation view of the bridge is shown in Fig. 1. The deck cross se

50、ction is an aerodynamically shaped closed- box steel girder 25.1 m wide and 2.8 m high as depicted in Fig. 2. The bridge towers are A-shaped steel-reinforced con- crete towers 175.5 m high as shown in Fig. 3. The eight g

51、roups of cables are composed of high strength steel wires 7 mm in diameter with from 73 to 199 wires per cable. The cable data are listed in Table 1. The stay cables are double arrangements. The three main bridge element

52、s of the example bridge, namely, steel girder, cables, and reinforced concrete towers are composed of three different materials. The weight per unit volume of each cable depends on the number of wires in in- dividual cab

53、les as shown in Table 1. The material data for the analyses are listed in Table 2. Table 3 gives the elastic-plastic hardening stress-strain data of the steel girder used in the anal- ysis. For FEM modeling, the girder i

54、s divided into 76 plane beam elements and each tower is divided into 32 plane beam ele- ments. Each cable is treated as a plane truss element. Because of the complex cross-section shape of the bridge, for simplic- ity, t

55、he equivalent thin-walled box section of the girder and towers are used (Ren 1997). The equivalent sections are ob- tained by equalizing the cross-section areas and section inertia moments of the girder and towers. The s

56、ection areas and in- ertia moments of the girder and towers are given in Figs. 2 and 3, respectively. The actual boundary conditions are as follows: the joint be- tween the main girder and left tower is a fixed hinge, wh

57、ereas another joint between the main girder and right tower is a movable hinge, and all side piers are movable hinge (roller) supports as shown in Fig. 1. The total loads of the example bridge consist of dead loads and l

58、ive loads. The girder dead load, qd, is taken as qd = 170 kN/m, which is determined mainly by the own weight of the steel girder. The built-in construction loads are included in the dead loads because the paper only stud