Fotografia de 1909 da construção da icónica ponte de Manhattan
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Fotografia de 1909 da construção da icónica ponte de Manhattan
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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 could 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. At the time the Manhattan Bridge was designed, this was the first occasion there had been an appropriate opportunity to use Melan’s 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 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 at carrying loads than stiffer forms of bridge. The new theory allowed the Manhattan Bridge to be designed to be lighter, 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 also carry subway trains. Despite the application of the new theory, after the initial use of the bridge, it became clear that there was a significant flaw in its design.
