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1、Proceedings of Bridge Engineering 2 Conference 200727 April 2007, University of Bath, Bath, UKCRITICAL ANALYSIS OF THE MANHATTAN BRIDGEJulian StadenDepartement of Civil and Architectural Engineering, University of Bath Abstract: This paper provides detailed information about the different aspects of
2、 the design of 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 short coming in the design of the structure and any ways in which the
3、engineers could have potentially improved the design of the bridge. Attention will also be paid to the ways in which the bridge would be 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.
4、Keywords: truss, stiffness, tension, deck, torsion Figure 1: Manhattan Bridge. View from Manhattan side.1 Overview of The Manhattan BridgeThe 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
5、 to provide another transport link between the two boroughs. Before construction began 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
6、 to span 448metres between piers, which was a somewhat shorter distance than the main spans of either the Brooklyn or Williamsburg bridges 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 st
7、ep forward in the progression of bridge building. The bridge was the first to be designed using deflection theory, which quickly replaced 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 aspec
8、t 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 Manhattan 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 su
9、spenders that hang from one of the four main cables. The four cables are supported by the two towers and are held down by anchorages 224metres 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
10、 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 small deflections. However, whilst this was an incorrect approximation, as suspended structures were
11、sometimes observed to undergo significant deflections, this was the only mathematical modelling that had been applied up to that time. 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
12、 of analysis allowed the engineers to design the bridge with a more accurate understanding of how it would actually perform, allowing a 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
13、main cables being more efficient acarrying loads than stiffer forms of bridge. The new 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
14、 normal circumstances .for example,if the bridge was to carry only vehicular traffic, but in the case of the Manhattan Bridge,it was to also carry subway trains. 朗读显示对应的拉丁字符的拼音Despite the application of the new theory, after the initialise of the bridge, it became clear that there was a significant
15、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 trusses 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 trai
16、ns 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 deflected 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
