桥梁设计外文翻译曼哈顿大桥的研究与分析Word文档下载推荐.docx

1、Julian StadenDepartement of Civil and Architectural Engineering, University of Bath Abstract: This paper provides detailed information about the different aspects of the design of the Manhattan Suspension Bridge. Analytical reasoning is given to why each design feature was designed in the manor it w

2、as in order to fulfil the engineers design criteria. An attempt is also made to illustrate any short coming in the design of the structure and any ways in which the engineers could have potentially improved the design of the bridge. Attention will also be paid to the ways in which the bridge would b

3、e designed and constructed if it were to be built in the 21st century. The reasons why design principals and construction methods have changed will also be outlined.Keywords: truss, stiffness, tension, deck, torsion Figure 1: Manhattan Bridge. View from Manhattan side.1 Overview of The Manhattan Bri

4、dgeThe Manhattan Bridge, although unfinished, was opened in 1909 and was the third bridge to span the East River running between Brooklyn and Manhattan. It was built to provide another transport link between the two boroughs. Before construction began there was a great deal of controversy over the p

5、roposed designs for the bridge. Eventually a fairly typical looking suspension bridge design was approved that was designed by engineer Leon Moisieff. The bridge was to span 448metres between piers, which was a somewhat shorter distance than the main spans of either the Brooklyn or Williamsburg brid

6、ges that neighbore it.Even though the Manhattan Bridge made no advancement in the spanned length achievable by a suspension bridge, it did represent a significant step forward in the progression of bridge building. The bridge was the first to be designed using deflection theory, which quickly replac

7、ed all previous methods of bridge design. The design also incorporated steel towers that were only braced in two dimensions rather than three. This was another aspect of bridge design that had not been seen prior to the building of the Manhattan Bridge.朗读显示对应的拉丁字符的拼音 The entire structure of the Manh

8、attan suspension bridge was to be designed in steel. The deck structure is comprised of four steel stiffening trusses that were each supported by regularly spaced suspenders that hang from one of the four main cables. The four cables are supported by the two towers and are held down by anchorages 22

9、4metres from each side of the main span. 2 Designing The Structure The Structure The Manhattan Bridge was the first suspension bridge to be designed using deflection theory in calculating how the horizontal deck and curved cables worked together to carry loads. Until this point, suspension bridges c

10、ould only be designed using elastic theory which meant assuming small deflections. However, whilst this was an incorrect approximation, as suspended structures were sometimes observed to undergo significant deflections, this was the only mathematical modelling that had been applied up to that time.

11、At the time the Manhattan Bridge was designed, this was the first occasion there had been an appropriate opportunity to use Melans deflection theory. This new method of analysis allowed the engineers to design the bridge with a more accurate understanding of how it would actually perform, allowing a

12、 greater economy of material usage.Deflection theory meant that all suspension bridges were proved to be stronger than previously considered due to the curve in the main cables being more efficient acarrying loads than stiffer forms of bridge. The new theory allowed the Manhattan Bridge to be design

13、ed to belighter, with smaller stiffening trusses, than it otherwise would have been using elastic theory. These smaller lighter trusses would have been acceptable in normal circumstances .for example,if the bridge was to carry only vehicular traffic, but in the case of the Manhattan Bridge,it was to

14、 also carry subway trains. Despite the application of the new theory, after the initialise of the bridge, it became clear that there was a significant flaw in its design.2.1 Inadequacy of DesignEach time a heavy subway train passed over the bridge, it caused local deflection of the stiffening trusse

15、s on the side of the deck of the trains passage. The deflection on one side induced torsion in the deck. This problem was further accentuated when trains began to pass over each side of the bridge in opposing directions at the same time. It was reported that at this point, each sideof the deck defle

16、cted by up to 1.2 meters, meaning a total relative deflection of over 2 meters. This put significant stresses into the bridge deck and subsequently lead to extensive repairs and stiffening work needing to becarried out in order to allow the bridge to remain serviceable. In my mind, the most obvious

17、failing in the design of the Manhattan Bridge is the location of the tracks subway .They have been located at each edge, rather than placing them in the central section of the deck, with road lanes separating them. Keeping the tracks close together would have reduced the length of the effective leve

18、r arm that the trainss live loading would have had, reducing the torsion moment induced.Although I am uncertain as to the design engineers reasoning behind locating the subway tracks in these positions, a possible reason becomes apparent when looking at a cross section of the deck.Figure 2: Cross se

19、ction showing location of lanes across deckFigure 3: The four main cables are not evenly separated.The figures illustrate that the main cables and corresponding stiffening trusses are “paired” on each side to enclose a region of deck resulting in a larger span of deck between them. As shown in figur

20、es 4 and 5 ,these enclosed regions are where the design engineers located the subway tracks and is where the distance between the stiffening trusses is smaller. The engineers would have realised that the heavy live loading from the subway trains would have caused a significantly greater degree of be

21、nding across the deck between stiffening trusses in comparison to the bending due to vehicular loading over the same span. Therefore it would have made sense to locate the lighter vehicular live loading over the larger span of deck in the region between the two pairs of trusses. By then locating the

22、 subway tracks in the smaller spanning regions of deck, the resulting bending moment from their load is far smaller than if they were located in the central section. This would have meant that the design bending moment across the whole deck could have been of a similar magnitude, allowing the suppor

23、ting deck structure to be designed more economically than otherwise using a section with a constant moment capacity across the whole deck. I.e. exactly the same the beam section could be used over the decks full width, resulting in simpler construction and less wasted material. These paired cables c

24、onsequently could have been designed in this way intentionally for the purpose of accommodating the subway tracks. It is possible therefore that the distribution of the load types across the deck in this configuration was a fundamental part of the design of the whole superstructure. As a great deal

25、of planning was most likely given to the most efficient location of the subway tracks as discussed above, it is unfortunate that the chosen configuration would go on to cause torsion in the deck.An alternative solution to changing the location of the subway tracks would have been to use deeper stiff

26、ening trusses. These would have helped prevent the deflection of the outer main cables and hence reduced torsion in the deck. However this would have resulted in a significant detrimental effect on the bridges aesthetic qualities.Overall the bridge was designed adequately in a two dimensional sense,

27、 but proper analysis appears not to been carried out in three dimensions, otherwise the torsional deflections could have been prevented.The whole process would be easily avoided in the design of a modern suspension bridge. Three dimensional finite element analysis software would be used in order to

28、check the structural capacity of the deck in longitudinal and transverse directions. 2.2 Tower DesignThe Manhattan Bridge was the first suspension bridge to be designed with towers braced only in a plane transverse to the deck.Figure 4: The towers are braced for stiffness in two dimensions, rather t

29、han threeMaking the towers flexible in the same plane as the main cables allows for any movement at the top of the towers to be taken as bending in the towers. The flexing of the towers prevents large bending moments being transferred straight to the foundations. Therefore smaller foundations under

30、the piers are needed compared to under more typical tower design for the time the bridge was designed and built. This is possible because the foundations would mostly be there to take the vertical load, rather than a combination of a vertical load and a large bending moment. The four main steel sect

31、ions that comprise each tower have however been braced with cross members in the transverse plane to the deck. Elasticity in this plane would be undesirable and of absolutely no benefit. The engineers would have been fully aware that without the bracing in this plane, the structure would be much mor

32、e unstable, and that the columns could potentially buckle under the load of the main cables supporting the deck.The design of the towers of the Manhattan Bridge was the first example of the application of many of the principals adopted in the design of modern suspension bridge towers.Towards the base of each pier, the steel section increases in size until it meets the masonry footing. These would have been designed in this manner