Suspension bridge

A suspension bridge is a type of bridge that has been made since ancient times. Simple suspension bridges, for use by pedestrians, are still constructed in some places worldwide for use by pedestrians and livestock using designs based upon the ancient Inca rope bridge. Suspended from two high locations over a river or canyon, simple suspension bridges follow a shallow downward arc and are not suited for modern roads and railroads. Over the centuries, advancements in materials and design led to the development of the suspended-deck suspension bridge, a modern bridge capable of carrying vehicles and light rail. Instead of the deck following a downward arc of the main load bearing cables (or chains) these cables are suspended between towers and the cables support vertical suspender cables to carry the weight of a deck below, upon which the traffic crosses. This arrangement allows the deck to be level or to arc slightly upward for additional clearance.

Disadvantages over other bridge types

• Lacking stiffness the bridge may become unusable in turbulent and strong wind conditions and so require temporary closure to traffic.
• Being flexible in response to concentrated loads the structure is generally not used for regional rail crossings, which concentrate the maximum "live" loading at the location of the locomotives.
• Under severe wind loading, the towers exert a large torque force in the ground, and thus require very expensive foundation work when building on soft ground.