The suspension bridge is supported by overhanging cables. Modern suspension bridges are stronger, lighter and more aesthetically pleasing than other types of bridges, allowing them to span greater distances. They are also among the most expensive to build. Although drawbridges could be built to support the weight of eight trains, almost all of them were designed for vehicular traffic.
Deflection theory has been used since the early 20th century to calculate how horizontal decks and curved cables work together to withstand loads. The buckling theory, first proposed by Aᴜsᴛʀɪᴀn academic Joseph Mellan in 1888, describes how decks and cables flex under the stress of gravity, reducing the required deck stiffness as spans lengthen and suspended structures become heavier. Warp theory greatly motivated engineers as they sought to reduce the beam’s depth-to-span ratio for a lighter, sleeker appearance without sacrificing safety.
construction
When building abutment bridges over water, the foundation is made by sinking a concrete caisson into the river bed. Large boxes or cylinders made of wood, metal or concrete are called caissons. Towers were built on top of caissons when there was a drawbridge. Originally made of stone, today’s suspension bridge towers are made of steel or concrete. Anchors are then constructed at both ends, often of reinforced concrete with steel lugs embedded in the concrete, to which the cables are attached. A piece of metal with holes at both ends is called an eye strip.
Early cable suspension bridges consisted of interlocking wrought iron rings; Today, however, cables are often made from thousands of mild steel cables spun together on site. Pulleys are used for rotation, transporting each cable through the top of the tower to the opposite, black anchor. To stop corrosion, the wires are bundled and sealed. The deck is then raised, usually by floating deck members on hsip, which are lifted by winches and attached to hangers after the wiring is complete.
