Civil Engineer Expert

The Rio-Antirio bridge in Greece

A cable-stayed bridge is a bridge that consists of one or more columns (normally referred to as towers or pylons), with cables supporting the bridge deck.

There are two major classes of cable-stayed bridges: In a harp design, the cables are made nearly parallel by attaching cables to various points on the tower(s) so that the height of attachment of each cable on the tower is similar to the distance from the tower along the roadway to its lower attachment. In a fan design, the cables all connect to or pass over the top of the tower(s).

The cable-stay design is the optimum bridge for a span length between that of cantilever bridges and suspension bridges. Within this range of span lengths a suspension bridge would require a great deal more cable, while a full cantilever bridge would require considerably more material and be substantially heavier. Of course, such assertions are not absolute for all cases.

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A simple suspension footbridge in Finland

A simple suspension bridge (also rope bridge, swing bridge (NZ), suspended bridge, and hanging bridge) is an early type of bridge that is supported entirely from anchors at either end, and has no towers or piers. However, it may have saddles. In such bridges, the deck of the bridge follows the downward and upward arc of the load bearing cables, with additional light ropes at a higher level used to form a handrail. Alternatively, stout handrail cables supported on short piers at each end)may be the primary load bearing element, with the deck suspended below. Suspended well from two high locations over a river or canyon, simple suspension bridges follow a shallow downward catenary arc and are not suited for modern roads and railroads. Owing to practical limitation in the grade (ie, the deck being an arc, not flat) and the response to dynamic loads of the bridge deck, this type is quite restricted in its load-carrying capacity relative to its span. Yet, this type of bridge is considered the most efficient and sustainable design in developing countries, especially for river crossings that lie in non-flood plain topography like gorges (www.footbridges.org).

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Suspension Bridge

 A suspension bridge is a type of bridge which is built by suspending the roadway from cables attached to a master cable which runs above the length of the bridge. In addition to being strong and lightweight, suspension bridges are also beautiful, and some of the most famous bridges in the world are also suspension bridges, including San Francisco’s iconic Golden Gate Bridge and New York’s Brooklyn Bridge. The design of a suspension bridge is simple and straightforward, and takes advantage of several techniques to distribute the weight of the bridge safely and evenly.

The basic design of a suspension bridge has been in use for centuries: thousands of years ago, people crossed waterways and chasms by swinging hand over hand on suspended cables. Later, walkways were hung from the cables to make the process easier, and the original vines and ropes began to be replaced with chains. Major bridges were still built using a truss design until 1808, when an American inventor named James Finley filed a patent on an early version of a suspension bridge. Finley’s design involved stretching two strong chains over the top of several towers and anchoring them on either side of the bridge. He hung lesser chains from the two master chains and used them to suspend a rigid deck, and the modern incarnation of the suspension bridge was born.

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Suspended-deck suspension bridge with a distinctly arched deck

A suspension bridge is a type of bridge in which the deck (the load-bearing portion) is hung below suspension cables on vertical suspenders. While modern bridges of this type date from the early 19th century, earlier bridges without vertical suspenders (simple suspension bridges) date from the 7th Century in Central America.

Suspended-deck suspension bridge with a distinctly arched deckThis type of bridge has cables suspended between towers, plus vertical suspender cables that carry the weight of the deck below, upon which traffic crosses. This arrangement allows the deck to be level or to arc upward for additional clearance. Like other suspension bridge types, this type often is constructed without falsework.

The suspension cables must be anchored at each end of the bridge, since any load applied to the bridge is transformed into a tension in these main cables. The main cables continue beyond the pillars to deck-level supports, and further continue to connections with anchors in the ground. The roadway is supported by vertical suspender cables or rods, called hangers. In some circumstances the towers may sit on a bluff or canyon edge where the road may proceed directly to the main span, otherwise the bridge will usually have two smaller spans, running between either pair of pillars and the highway, which may be supported by suspender cables or may use a truss bridge to make this connection. In the latter case there will be very little arc in the outboard main cables.

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