Suspension bridge

A suspension bridge is one of the types of bridges in which the Deck(the load bearing portion) is hung below suspension cables on vertical suspenders.

The cables (or ropes or chains) are strung across the river through two tall towers.

Suspension bridges are aesthetic, light, and strong.

Suspension bridges can span distances from 2,000 to 7,000 feet—far longer than any other kind of bridge.

True to its name, a suspension bridge suspends the roadway from huge main cables, which extend from one end of the bridge to the other.

Suspension bridges built over waterways, can be built high, allowing the passage of tall ships unhindered by the bridge.

During construction, temporary central supports do not need to be built, and access to the construction is not required from beneath.

This means busy roadways and waterways do not need to be disrupted.

The added flexibility of suspension bridges allows them to flex under the power of winds and earthquakes

They tend to be the most expensive to build.

Suspension bridges can be unstable in extremely turbulent conditions, with extreme cases requiring temporary closure of the bridge.

When built in soft ground, suspension bridges require extensive and expensive foundation work to combat the effects of the heavy load on foundation towers.

Flexibility can be a disadvantage to suspension bridges, which can flex under heavy, concentrated loads. Suspension bridges are not generally used for regional rail crossings that carry maximum weight loads, causing added stress on the bridge.

The main Parts of a
Suspension Bridge are
Deck
Suspension cable
Suspender
Tower
Floor beams
Backstay
Anchorage Block ( Dead man )
Approach ramp

Suspension bridge has cables suspended between towers.

The towers enable the main cables to be draped over long distances.

The main cables continue beyond the pillars to deck-level supports, and further continue to connections with anchors in the ground.

Most of the weight of the bridge is carried by the cables to the anchorages, which are imbedded in massive concrete blocks.

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.

Inside the anchorages, the cables are spread over a large area to evenly distribute the load and to prevent the cables from breaking free.

The vertically suspended cables are known as suspenders.

Vertical suspended cables carry the weight of the deck below, upon which traffic crosses.

The roadway is supported by vertical suspender cables or rods, called hangers.

The main suspension cable in the early nineteenth century was often made from chain or linked bars, but modern bridge cables are made from multiple strands of wire.

The reason is that as spans increased, engineers were unable to lift larger chains into position, whereas wire strand cables can be largely prepared in mid-air from a temporary walkway.

The cables are made of individual steel wires bound tightly together, which is very strong under tension, is an ideal material for cables. A single steel wire, only 0.1 inch thick, can support over half a ton without breaking.

Suspension bridges have caused disasters in the past because of these cables.

As said that in early stages suspension bridges were made using chain links of heavy steel for the main cable.

If only one chain link failed, the whole bridge would collapse, as what happened to the Silver Bridge in 1967, killing 46 people.

Because of these reasons, suspension bridges use bundles of cables in recent time as said earlier. If one or two of the cables fails, the bridge still stays intact.

Three kinds of forces operate on any bridge: the dead load, the live load, and the dynamic load.

Dead load refers to the weight of the bridge itself.

Live load refers to traffic that moves across the bridge.

Dynamic load refers to environmental factors such as sudden gusts of wind and earthquakes

The main forces in a suspension bridge of any type are tension in the cables and compression in the pillars.

The force of compression pushes down on the suspension bridge's deck, but because it is a suspended roadway, the cables transfer the compression to the towers, which dissipate the compression directly into the earth where they are firmly entrenched.

The supporting cables, running between the two anchorages, are the lucky recipients of the tension forces.

The anchorages are also under tension, but since they are held firmly to the earth, the tension they experience is dissipated.

Since almost all the force on the pillars is vertically downwards and they are also stabilized by the main cables, the pillars can be made quite slender.

The weight is transferred by the cables to the towers, which in turn transfer the weight to the ground.

The following opposing forces act on the deck & the suspension cable:

one downward force caused by the load of the roadway.

one force in one part of the cable, pulling up and to the left.

one force in the other part of the cable, pulling up and to the right.

In the modern world, the longest suspension bridge is Japan's Akashi Kaikyo Bridge, which spans 6,432 feet.

Today, wind tunnel testing of bridge designs is mandatory. Lake of this disaster may occur.

So with these specifications we can conclude that in some special conditions Suspension bridges are more reliable than any other.