1、<p>　　Proceedings of Bridge Engineering 2 Conference 2007</p><p>　　27 April 2007, University of Bath, Bath, UK</p><p>　　CRITICAL ANALYSIS OF THE MANHATTAN BRIDGE</p><p>　　Julia

2、n Staden</p><p>　　Departement of Civil and Architectural Engineering, University of Bath</p><p>　　Abstract: This paper provides detailed information about the different aspects of the design of

3、the Manhattan Suspension Bridge. Analytical reasoning is given to why each design feature was designed in the manor it was in order to fulfil the engineers’ design criteria. An attempt is also made to illustrate any shor

4、t 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 t</p><p>　　Keywords: tru

5、ss, stiffness, tension, deck, torsion </p><p>　　Figure 1: Manhattan Bridge. View from Manhattan side.</p><p>　　1 Overview of The Manhattan Bridge</p><p>　　The Manhattan Bridge, alt

6、hough 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 be

7、gan there was a great deal of controversy over the proposed 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

8、 span 448metres between piers, whic</p><p><b>　　朗讀</b></p><p>　　顯示對應的拉丁字符的拼音</p><p>　　The entire structure of the Manhattan suspension bridge was to be designed in steel

9、. 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 a

10、re held down by anchorages 224metres from each side of the main span. </p><p>　　2 Designing The Structure </p><p>　　The Structure The Manhattan Bridge was the first suspension bridge to be desig

11、ned using deflection theory in calculating how the horizontal deck and curved cables worked together to carry loads. Until this point, suspension bridges could only be designed using elastic theory which meant assuming s

12、mall 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 h</p><p&

13、gt;　　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 ne

14、w theory allowed the Manhattan Bridge to be designed to belighter, with smaller stiffening trusses, than it otherwise would have been using elastic theory. These smaller lighter trusses would have been acceptable in norm

15、al circumstances .for example,if the bridge was to carry only veh</p><p><b>　　朗讀</b></p><p>　　顯示對應的拉丁字符的拼音</p><p>　　Despite the application of the new theory, after the

16、initialise of the bridge, it became clear that there was a significant flaw in its design.</p><p>　　2.1 Inadequacy of Design</p><p>　　Each time a heavy subway train passed over the bridge, it ca

17、used local deflection of the stiffening trusses on the side of the deck of the train’s passage. The deflection on one side induced torsion in the deck. This problem was further accentuated when trains began to pass over

18、each side of the bridge in opposing directions at the same time. It was reported that at this point, each sideof the deck deflected by up to 1.2 meters, meaning a total relative deflection of over 2 meters. This put sign

19、</p><p>　　In my mind, the most obvious 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

20、 of the deck, with road lanes separating them. Keeping the tracks close together would have reduced the length of the effective lever arm that the trains’s live loading would have had, reducing the torsion moment induced

21、.</p><p>　　Although I am uncertain as to the design engineer’s reasoning behind locating the subway tracks in these positions, a possible reason becomes apparent when looking at a cross section of the deck.&

22、lt;/p><p>　　Figure 2: Cross section showing location of lanes across deck</p><p>　　Figure 3: The four main cables are not evenly separated.</p><p>　　The figures illustrate that the mai

23、n 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. </p><p>　　As shown in figures 4 and 5 ,these enclosed regi

24、ons 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

25、 have caused a significantly greater degree of bending 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

26、 lighter veh</p><p>　　As a great deal 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

27、cause torsion in the deck..</p><p>　　An alternative solution to changing the location of the subway tracks would have been to use deeper stiffening trusses. These would have helped prevent the deflection of

28、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.</p><p>　　Overall the bridge was designed

29、adequately in a two dimensional sense, but proper analysis appears not to been carried out in three dimensions, otherwise the torsional deflections could have been prevented.</p><p>　　The whole process would

30、 be easily avoided in the design of a modern suspension bridge. Three dimensional finite element analysis software would be used in order to check the structural capacity of the deck in longitudinal and transverse direc

31、tions. </p><p>　　2.2 Tower Design</p><p>　　The Manhattan Bridge was the first suspension bridge to be designed with towers braced only in a plane transverse to the deck..</p><p>　　F

32、igure 4: The towers are braced for stiffness in two dimensions, rather than three</p><p>　　Making the towers flexible in the same plane as the main cables allows for any movement at the top of the towers to

33、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 the piers are needed compared to under more t

34、ypical 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</p><p>　　The four main steel sections that

35、 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. </p><p>　　The engineers would

36、 have been fully aware that without the bracing in this plane, the structure would be much more unstable, and that the columns could potentially buckle under the load of the main cables supporting the deck.</p>&l

37、t;p>　　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.</p><p>　　Towards the bas

38、e of each pier, the steel section increases in size until it meets the masonry footing. These would have been designed in this manner for two reasons. Firstly, the larger area where the steel meets the masonry would be a

39、dvantageous in creating a greater area for the steel to bear onto, spreading the load spread evenly over the masonry. Secondly, the larger area of steel meeting the masonry would have made it more possible to form a fixe

40、d connection that didn’t allow any rotation.</p><p>　　It appears that the steel piers broaden as they approach the underside of the deck, implying a moment resisting connection. Although this is not the case

41、 as the vast majority of this steel is for non-structural purposes, explained previously. However, one practical use it does serve is to act as a cantilever supporting the pedestrian walkway to take it around the towers.

42、 Considering there is no fixed connection between the support piers and the deck trusses, it would be presumed that there would</p><p>　　The four main cables are not fixed to the top of the towers. Instead t

43、hey are free to slide over their supports. This is to prevent any deflection of the main span causing a huge bending moment in the foundation. The connection between the cables and the tower is made directly above each o

44、f the four columns, so that the load supported by the cables is directed only into an axial load on each column. This allows for the four columns comprising each tower to be relatively slender.</p><p>　　2.3

45、Construction</p><p>　　As with any suspension bridge, the Manhattan Bridge would have required very large foundations. These foundations would have most likely had to have gone down to bedrock, to ensure that

46、 there would be no settlement of the piers. The bridge piers are located within the East River. Each foundation would have been built by floating a caisson to the desired location and then sinking it using very heavy wei

47、ghts. The caissons would have probably been made from timber braced with steel. </p><p>　　After workers had removed all the soil and debris, the caissons would have been filled with concrete to form the foun

48、dations. After the foundations would have been completed, the towers would then have been erected. These would be able to stand with no propping due to the fixed connection at their base.</p><p>　　Figure 5:

49、The erected towers</p><p>　　Each tower measured 102.4 meters in height. Construction would have comprised of bolting together relatively small sections of steel, using the masonry pier as a platform to work

50、up from. Bracing would have been bolted onto the main structure as the structure increased in height, ensuring stability. </p><p>　　After the completion of the towers, the main cables would then be spun. Ea

51、ch of the four main cables are comprised of 9472 individual wires, making the total cable thickness come to 0.54 meters in diameter. These main cables each run through a corresponding saddle on the top of the towers. The

52、 ends of the cables would have been fixed into the anchorages, probably by wrapping the strands around massive steel I bars. These would then have been embedded within the huge masonry anchorages, which wou</p>&l

53、t;p>　　Figure 6: The towers and main cables are in position but there are no suspending cables or deck at this stage.</p><p>　　Figure 7: Section through the anchorage showing restraint of the cable.</p&

54、gt;<p>　　Figure 8: Large masonry anchorages tie down the main cables. The anchorage shown is on the Manhattan side. </p><p>　　From the main cables, steel cable suspenders would have then been hung at

55、regular intervals across the length of the suspended section of the bridge. This then allowed the deck to begin to be fixed to the suspenders. This was done starting at each tower and working in both directs towards the

56、opposing tower and the anchorages. </p><p>　　Currently, common practice is to begin this process from the centre of the span. However at the time the Manhattan Bridge was built, this would have been very imp

57、ractical, as there would have been no simple means of lifting materials or plants to this location. The building of the deck was however carried out symmetrically in each direction. This is an important aspect in suspens

58、ion bridge construction as it avoids any asymmetrical deflection of the deck, which would add an unnecessary complexit</p><p>　　Figure 9: The deck was built from each tower at the same rate towards the middl

59、e of the span</p><p>　　3 Susceptibility to Intentional Damage</p><p>　　When the Manhattan Bridge was designed, there was probably very little thought given to the idea that somebody might purpos

60、ely try to destroy it. In some rare cases, potential acts of vandalism would need to be considered when designing a structure. However, a very large structure like the Manhattan Bridge would have no areas regarding the b

61、ridges structural integrity that would be susceptible to vandals. When designing such structures today, careful consideration needs to be given to what may h</p><p>　　Without detailed calculation it is very

62、hard to look at the existing bridge structure and judge whether it would collapse completely if certain parts were taken away. In order to try to go about this analysis, the key structural elements that form the core str

63、ucture of the suspension bridge must be first identified. These are: the main cables, the towers, the suspenders and the anchorages. The deck is not included in this list, as it is not actually supporting anything. This

64、 implies that if a s</p><p>　　Holding the deck up is the suspenders. These are regularly spaced hanging from the main cables, and fixed to the Warren trusses. At 7.4 metres in depth, these trusses would be a

65、ble to span a far, far greater distance than that of the spacing between the suspenders supporting them, even with the dead load on the deck acting over the spanned length. The reason for their massive depth is so there

66、is very little deflection due to live loading, meaning the only implication of them spanning further wo</p><p>　　The most catastrophic collapse could probably only take place if the towers, piers or anchorag

67、es of the Manhattan bridge were destroyed. This is because these are the elements that keep the whole of the suspended structure up. The engineers building the bridge would have realised the structural significance of th

68、ese elements and would have presumably used a factor of safety that reflects this.</p><p>　　Overall, no amount of planning in the design of the bridge could ever make it immune to intentional damage, however

69、 if enough thought it given, then a significant loss of life could be avoided if the situation were to ever arise.</p><p>　　References </p><p>　　[1] Sharon Reier 1977 The Bridges of New York. &l

70、t;/p><p>　　[2]Thomas R Winpenny Manhattan Bridge the troubled storey of a New York monumen. </p><p>　　[3] Sharon Reier 1977 The Bridges of New York.</p><p>　　http://en.structurae.de/s

71、tructures/data/photos.cfm?ID=s0000529 </p><p>　　http://en.structurae.de/structures/data/index.cfm?ID=s000052</p><p>　　Bibliography</p><p>　　Thomas R Winpenny. Manhattan Bridge,the t

72、roubled storey of a New York monument. Sharon Reier 1977 The Bridges of New York </p><p>　　www.nycsubway.org</p><p>　　www.ncyroads.com</p><p>　　Weidlinger Associates.，</p>&l

73、t;p>　　http://www.wai.com/Transportation/Bridges-long/manhattan.html</p><p>　　公路go橋梁工程 2007年第2個會議</p><p>　　2007年4月27日，巴斯，英國巴斯大學</p><p>　　曼哈頓大橋研究與分析</p><p><b>　　

74、朱利安斯塔登</b></p><p>　　英國巴斯大學，土木建筑學院</p><p>　　摘要：本文詳細的闡述了有關(guān)曼哈頓大橋設(shè)計的各個方面。分析推理它的每一個典型的設(shè)計特點，是為了讓我們的設(shè)計能夠更好的滿足設(shè)計標準。也試圖說明，在這些結(jié)構(gòu)設(shè)計中存在的缺陷和一些工程師們所采用的橋梁設(shè)計的改進方法。還將注意到可能會在21世紀橋梁建設(shè)中用到的設(shè)計和建造方法。同時也概述，曼哈頓大橋?qū)?/p>

75、致現(xiàn)在懸索橋設(shè)計原則和施工方法發(fā)生了改變的原因。</p><p>　　關(guān)鍵詞：桁架，剛度，張力，橋面，扭轉(zhuǎn)</p><p>　　圖1：從曼哈頓大橋的一面看</p><p><b>　　1曼哈頓大橋概述</b></p><p>　　曼哈頓大橋，盡管沒有完成，但在1909年開通啟用了，是第三座跨越布魯克林和曼哈頓之間河流的橋

76、梁。它是為在布魯克林和曼哈頓之間提供另外一條運輸通道而建設(shè)的。施工前開始，發(fā)生了許多關(guān)于這座橋梁設(shè)計方案的爭論。最終批準了一個相當?shù)湫偷挠晒こ處烲eon Moisieff.設(shè)計懸索橋方案。這座橋兩個橋墩之間相距448米，比與它相鄰的布魯克林大橋或威廉斯伯格大橋的主跨要小一些。雖然曼哈頓橋在懸索橋跨越能力上沒有取得什么進步，但它在橋梁建設(shè)發(fā)展的歷程中邁出了非常重要的一 步。它首次突破性地采用撓度設(shè)計理論，并且迅速取代了以前懸索橋所使用的設(shè)

77、計方法。鋼塔采用的是二維支撐而不是以前的三維支撐。這些橋梁設(shè)計方法在曼哈頓橋建成之前是沒有的，。</p><p><b>　　2結(jié)構(gòu)設(shè)計</b></p><p>　　曼哈頓大橋是第一座在水平橋面板與主纜如何共同承受荷載計算中采用撓度理論的懸索橋。直到此時，懸索橋只能利用基于小撓度假設(shè)的彈性理論進行設(shè)計。不過，這個假設(shè)并不是非常準確。采用懸浮結(jié)構(gòu)進行了觀察，我們發(fā)現(xiàn)有時

78、會出現(xiàn)重大撓度。但這是那個時候可以使用的唯一的數(shù)學模型。直到曼哈頓橋的設(shè)計出現(xiàn),才使得Melan的撓度理論第一次有了一個合適的運用機會。這種新的分析方法使得工程師們，可以更加準確的理解實際情況，從而使得材料的使用更加的經(jīng)濟。</p><p>　　撓度理論表明，懸索橋由于曲線主纜能更有效率的承載負荷因而比起其它剛性的橋梁具有更大跨度。比彈性理論，這個新理論能夠讓曼哈頓橋設(shè)計成更輕的加勁桁架形式。這些更小更輕的桁架在

79、正常情況下是可以接受的，例如如果橋是只是承受車輛荷載，但是事實上，曼哈頓大橋還可以設(shè)置地鐵。盡管應用了新理論，但是在橋梁的建設(shè)初期，設(shè)計中仍然存在很明顯的缺陷。</p><p><b>　　朗讀</b></p><p>　　顯示對應的拉丁字符的拼音</p><p><b>　　2.1設(shè)計不足</b></p>

80、<p>　　每次重量很大的的地鐵列車在橋上通過時，會造成對列車通過處橋面板邊緣桁架加勁梁的偏轉(zhuǎn)，一側(cè)的變形會引起的橋面板的扭轉(zhuǎn)。當列車在同一時間沿先放到方向駛過時，問題會進一步加劇。據(jù)報道，在這這中情形下，橋面板偏轉(zhuǎn)可達1.2米，意味著相對撓度會超過2米。這使得強大的壓力進入橋面，從而為了橋能正常工作，維修工作會變得更加的困難和更加的頻繁。</p><p>　　在我看來，在曼哈頓大橋的設(shè)計中最明顯的缺陷

81、是地鐵的軌道位置。地鐵的軌道位置被設(shè)計在橋面的兩邊，而不是將其設(shè)計在橋面板的中央部分與道路分隔車道。保持緊密會減少軌跡的長度,火車的直接荷載產(chǎn)生有效杠桿臂，這減少扭力的產(chǎn)生。</p><p>　　雖然我不確定為地鐵的設(shè)計的工程師的是如何推理進而確定這些軌道的位置。但是，當我們從橋面板的橫截面看，原因似乎很明顯。 </p><p>　　圖2：在橋面板中心線處位置的橫截面</p>

82、<p>　　圖3：四個不均勻分開的主纜</p><p>　　這些數(shù)字說明，主纜和對應的加勁桁架在每邊靠近橋面板區(qū)域“配對”，導致在它們之間產(chǎn)生了較大的跨度。</p><p>　　正如圖4和圖5顯示的，設(shè)計工程師將地鐵軌道設(shè)計在這些地區(qū)，并使得加勁桁架之間的距離變得較小。工程師們將會意識到，在相同的跨徑下，相比車輛荷載而言，直接作用的重載荷的地鐵列車可能會在甲板上彎曲加勁桁架之間

83、明顯增加的變形。因此，它會作出來尋找生活的打火機車輛甲板以上的較大的桁架之間的兩對跨區(qū)域的負荷。屆時定位在較小的地鐵橫跨甲板區(qū)域軌道，從他們所產(chǎn)生的彎曲力矩遠遠小于如果他們是在位于中央部分。這將意味著，在整個設(shè)計彎曲甲板時刻可能有一個類似的規(guī)模已，使甲板結(jié)構(gòu)的配套設(shè)計更經(jīng)濟的狀態(tài)下使用橫跨整個甲板恒轉(zhuǎn)矩能力的部分。即一模一樣的梁節(jié)可反復使用的甲板的寬度，在簡單的建設(shè)，減少浪費的材料造成。這些成對電纜因而可能是故意這樣設(shè)計為容納地鐵軌道的

84、目的。因此，有可能對整個甲板負載類型分布在此配置是一個整個上層建筑設(shè)計的基本組成部分。</p><p>　　由于大量的規(guī)劃是最有可能給予最有效的地鐵軌道位置如上所述，但不幸的是，選擇的配置將繼續(xù)在甲板上造成扭轉(zhuǎn)..</p><p>　　另一種解決方案，改變了地鐵軌道位置將是利用深加勁桁架。這些將有助于防止外部主纜撓度，從而減少了甲板上扭??轉(zhuǎn)。然而，這將導致重大不利影響的橋梁美學特質(zhì)...

85、</p><p>　　整體橋梁的設(shè)計在二維空間設(shè)計的很合理，但似乎沒有適當?shù)姆治鋈S空間的情況，否則扭轉(zhuǎn)變形本來是可以避免的。</p><p>　　整個過程將容易地避免了在現(xiàn)代懸索橋的設(shè)計。三維有限元分析軟件將被使用，以測試橋面板在縱向和橫向的結(jié)構(gòu)能力。 </p><p><b>　　2.2塔設(shè)計 </b></p><

86、;p>　　曼哈頓大橋是第一座設(shè)計成塔與梁懸浮的懸索橋。</p><p><b>　　圖4：塔身</b></p><p>　　使塔靈活在同一平面為主要電纜允許任何運動在頂部的塔被視為彎曲在塔上。防止屈曲的大型彎矩塔樓直接到被轉(zhuǎn)移的基礎(chǔ)。因此較小的基礎(chǔ)橋墩下相比，更需要下典型塔的設(shè)計，爭取時間，這座橋是設(shè)計和建造的。這是有可能的，因為在那里基礎(chǔ)最能采取垂直荷載作用下

87、，而不是一個垂直荷載作用下形成的組合和一個大型的彎矩。</p><p>　　四個主要部分構(gòu)成各種塔鋼支撐和十字但已有成員在橫平面到甲板上。在這架飛機將彈性不良而根本沒有益處。</p><p>　　工程師將被充分認識到，如果沒有這架飛機在支撐，結(jié)構(gòu)會更加不穩(wěn)定，而且可能列扣下了支持主纜甲板負荷。 </p><p>　　在曼哈頓大橋的設(shè)計是塔的，在現(xiàn)代懸索橋塔設(shè)計采用了

88、多個應用校長的第一個例子。 </p><p>　　對各墩基礎(chǔ)的增加，鋼截面尺寸，直到它滿足了砌體落腳的地方。這些是設(shè)計以這樣的方式，原因有兩個。首先，較大的區(qū)域，那里的鋼符合砌體優(yōu)先創(chuàng)造一個更大范圍內(nèi)對鋼承受到的生產(chǎn)、傳播負荷均勻地鋪在橫梁。其次，在大范圍內(nèi)蒸壓加氣混凝土砌體的鋼會議將使它更能形成一種固定連接，不允許任何的旋轉(zhuǎn)。</p><p>　　看起來在鋼橋墩作為他們接近拓寬尾部的甲板

89、上這意味著耐震梁柱連接。雖然這里的情況是不像絕大多數(shù)這種鋼是為非構(gòu)造的目的之前解釋。然而它確實服務的一項實際使用是充當懸臂支護行人長廊把它周圍的高樓?？紤]到還沒有固定連接甲板桁架橋墩和支持它將會被認為會有軸承在這一點。這將允許這個橋梁回復任何運動由于風、溫度和生活沒有把巨大的應力加載到甲板結(jié)構(gòu)。</p><p>　　四個主要的電纜不固定至最高的塔。相反他們可以自由地滑過他們的支持。這是為了避免任何引起的大跨度的偏

90、轉(zhuǎn)一個巨大的彎矩的基礎(chǔ)。之間的連接電纜和塔是由直接在上面的每一個四柱使負荷是為了支持的電纜僅成一個軸向載荷在每一欄。這允許四柱包括每座塔是相對苗條。</p><p><b>　　2.3建設(shè)</b></p><p>　　正如其它的懸索橋一樣，曼哈頓大橋?qū)⑿枰浅４蟮幕A(chǔ)。這些基金會將很可能不得不有所下降到基巖，以確保不會有解決的碼頭。橋墩都設(shè)在東河。每個基金會將已建成一

91、個沉箱浮到所需位置，然后下沉它使用非常沉重的砝碼。沉箱將有可能被制成木材與鋼支撐。</p><p>　　工人在拆除后，所有的土壤和碎片，沉箱將被填充混凝土形成的基礎(chǔ)。會后，基金會已經(jīng)完成，便被塔建造。這將是經(jīng)得起支撐，由于沒有在他們的基地固定連接。</p><p>　　每座塔的高度一百零二點四米測量。建筑將有共同組成的支護鋼相對較小的部分，并以此作為一個平臺，工作從砌筑碼頭。本來螺栓支撐到

92、主結(jié)構(gòu)作為結(jié)構(gòu)，增加高度，確保穩(wěn)定。</p><p>　　在塔建成后，主纜然后將打滑。四是主纜每9472個人組成的線，使總厚度來電纜直徑0.54米。通過對其中的每個塔的頂部的相應薩德爾魯恩主纜。兩端會被固定于錨地可能是由環(huán)繞著大量的鋼鐵我酒吧的股，電纜的。這些便被嵌入在巨大的磚石錨地，這將防止任何主纜滑。這些碇泊處將工作重心，有一個龐大的自重。</p><p>　　圖6：塔和主纜中的位置&

93、lt;/p><p>　　圖7：通過顯示電纜的克制錨固段。</p><p>　　圖8：大砌體錨地牽制主纜。錨地顯示是在曼哈頓。</p><p>　　從主電纜，鋼纜吊桿將然后被掛在對面的橋長定期暫停部分。這就使甲板開始被固定在吊桿。這樣做是開始在每個塔和工作都對對方塔和錨碇指示。</p><p>　　目前，一般的做法是開始從跨度中心這一進程。然而在曼

94、哈頓大橋建成時間，這將是非常不切實際的，因為會被解除材料或植物到這個位置沒有簡單的方法。甲板的大樓進行了對稱但在每個方向。這是在吊橋建設(shè)的重要方面，因為它避免了任何的甲板，這會增加不必要的復雜性及其構(gòu)建不對稱偏轉(zhuǎn)。</p><p>　　圖9：建于甲板上以同樣的速度朝中間的跨度從每個塔</p><p><b>　　3故意傷害</b></p><p&g

95、t;　　當曼哈頓大橋的設(shè)計，有可能很少想過這些的想法，有人可能故意試圖摧毀它。在某些罕見情況下，潛在的破壞行為，就需要設(shè)計時必須考慮到一個結(jié)構(gòu)。然而，像曼哈頓大橋結(jié)構(gòu)將有非常大的地區(qū)就沒有橋梁的結(jié)構(gòu)完整性，將可能會受到破壞者。在設(shè)計這種結(jié)構(gòu)的今天，需要認真考慮考慮會發(fā)生什么事情的結(jié)構(gòu)，如果其中的一部分被有意摧毀，即是恐怖主義行為。設(shè)計者需要考慮是否可以繼續(xù)站立的結(jié)構(gòu)，即使某些關(guān)鍵內(nèi)容被完全拆除。這種設(shè)計在結(jié)構(gòu)方面是不常見的，和一個吊橋的

96、設(shè)計會不會例外。</p><p>　　如果沒有詳細的計算是非常努力尋找在現(xiàn)有橋梁??結(jié)構(gòu)和判斷是否會全面崩潰，如果某些部分被帶走。為了設(shè)法去左右這些分析，關(guān)鍵是形成了懸索橋結(jié)構(gòu)要素的核心結(jié)構(gòu)，必須首先確定。它們是：主電纜，塔，吊桿和錨地。甲板不包括在此列表，因為它實際上不是支持什么。這意味著，如果它的部分被刪除了，橋仍然立場。這座橋顯然是形同虛設(shè)，但至少不會是災難性的結(jié)構(gòu)崩潰。甲板上舉行，是吊帶。這些經(jīng)常掛間隔從

97、主電纜，并固定在華倫桁架。在水深7.4米，這將能夠桁架跨度遠遠更大的距離比吊桿支持他們之間的間距，即使在上甲板跨越長度恒載作用。對于他們巨大的深層原因是很少有這樣偏轉(zhuǎn)由于活荷載，意思是他們唯一的意義將是一個跨越進一步大量的偏轉(zhuǎn)。因此，我可以自信地假設(shè)，如果幾個衣架，彼此相鄰，沿被拆除，在甲板上，以及其他的結(jié)構(gòu)，將保持不變。也許最重要的一點是，是否可以繼續(xù)站立的結(jié)構(gòu)，如果主纜之一是通過失敗完全是恐怖主義行為。這是很難判斷，作為其他元素的橋

98、梁這么多貢獻力量。然而，一個粗略的指南可以采取從對計算結(jié)果進行一些有關(guān)以前。在第6.1我的計算，主纜與安全系數(shù)為2.6的設(shè)計。假設(shè)這個數(shù)字將會為這項工作的目的正確的，我們可以說，在主</p><p>　　最災難性的崩潰都可能發(fā)生，如果只有塔，碼頭或錨地的曼哈頓大橋被摧毀。這是因為這些元素是保持懸浮結(jié)構(gòu)整體了。大橋建設(shè)的工程師將已經(jīng)意識到了這些元素的結(jié)構(gòu)意義，將有大概使用了安全因素，反映了這一點。</p>

99、;<p>　　總的說來，沒有規(guī)劃中的橋梁設(shè)計金額可能永遠使免疫故意傷害，但是如果認為它給予足夠的，那么生命的重大損失是可以避免的，如果是有史以來的情況出現(xiàn)。 </p><p><b>　　參考文獻： </b></p><p>　　[1]莎朗Reier 1977年的橋梁紐約; </p><p>　　[2]托馬斯·R Win

100、penny 曼哈頓橋翻騰的層樓的住宅紐約的紀念碑;</p><p>　　[3]莎朗Reier 1977年紐約的橋梁;</p><p>　　http://en.structurae.de/structures/data/photos.cfm?ID=s0000529 </p><p><b>　　參考書目： </b></p><

101、p>　　托馬斯·R Winpenny 曼哈頓橋、翻騰的層樓的住宅紐約的紀念碑;莎朗Reier 1977年紐約的橋梁</p><p>　　www.nycsubway.org</p><p>　　www.ncyroads.com</p><p>　　Weidlinger Associates，</p><p>　　http://w