A Suspension Bridge

by ce on November 22, 2014

A suspension bride is a type of bridge where the main load-bearing elements are hung from suspension cables. While modern suspension bridges with level decks date from the early 19th century, earlier types are reported from the 3rd century BC. Simple suspension bridges for use by pedestrians and livestock, are still constructed, based upon the ancient Inca rope bridge.

Suspended well 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. Advances 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 the downward arc of the main load-bearing cables (or chains), these cables are suspended between towers, and vertical suspender cables carry the weight of the deck below, upon which traffic crosses. This arrangement allows the deck to be level or to arc slightly upward for additional clearance.

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.

The main forces in a suspension bridge are tension in the main cables and compression in the pillars. Since almost all the force on the pillars is vertically downwards and they are also stabilized by the main cables, the pillars ca be made quite slender, and they have been in, for example, the Severn Bridge, near Bristol, England.

Assuming a negligible weight as compared to the weight of the deck and vehicles being supported, a suspension bridge’s main cables will form a parabola (very similar to a catenary, the form the unloaded cables take before the deck is added). This can be seen from the cable’s constant gradient increase with linear (deck) distance, this increase in gradient at each connection with the deck providing a net upward support force. Combined with the relatively simple constraints place upon the actual deck, this makes the suspension bridge much simpler to design and analyze than a cable-stayed bridge, where the deck is in compression

 

Advantage over other bridge types

A suspension bridge can be made out of simple materials such as wood and common wire rope.

  • Longer main spans are achievable than with any other type of bridge
  • Less material may be required than other bridge types, even at spans those can achieve, leading to a reduced construction cost
  • Except for installation of the initial temporary cables, little access from below is required during construction, for example allowing a waterway to remain open while the bridge is build above
  • May be better able to withstand seismic movements than heavier and more rigid bridges

 

Disadvantage compared with other bridge types

  • Considerable stiffness or aerodynamic profiling may be required to prevent the bridge deck vibrating under high winds
  • The relatively low deck stiffness compared to other types makes it more difficult to carry heavy rail traffic where high concentrated live loads occur
  • Some access below may be required during construction, to lift the initial cables or to lift deck units. This access can often be avoided in cable-stayed bridge construction.

 

{ 1 comment… read it below or add one }

mmmmmm December 8, 2016 at 3:11 pm

please help me about suspension bridge in abaqus

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