Advantages of Suspension Bridges

Suspension bridges are adopted in places where it is difficult to construct other type of bridges. For very large spans, they can be adopted economically.

·         In a suspension bridge, tensile stresses are predominant. Thus it requires high tensile ropes, which are economical than mild steel trusses etc.

·         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 stresses are directly passed to the supports through cables and suspenders, hence slender sections are required effecting overall economy.

·         The area spanned by a suspension bridge is very long in proportion to the amount of materials required to construct bridges.

·         They are light and require no false work.

·         The material of construction can be transported easily.

·         The time of construction is less.

·         They provide the roadway at a low elevation and have low centre of wind pressure.

·         They give good aesthetic appearance.

·         They require no centering for construction.

·         There is no likely hood of failure during erection and after construction.

·         It is the safest structure as cables have vast reserve strength.

·         The chords of the stiffening truss can be repaired without interruption to traffic, while in other bridges the failure of a single truss member causes collapse of the bridge.

  What are the advantages/disadvantages of beam,arch, and suspension bridges?

Consideration Selection of Bridge Site

Consideration Selection of Bridge Site

Before a bridge is constructed, a suitable site is selected based on certain factors which have bearing on the economy and stability of the bridge.

1. At bridge site the reach of the stream should be straight.

2. The site should be geologically sound i.e. it should be away from fault zone, and should have unyielding, non erodible foundation for abutments and piers.

3. At the site, the stream should be narrow with well defined and firm banks.

4. At site the river flow should be without whirls and cross currents.

5. At the site there should be suitable high banks above high flood level on each side.

6. The approaches should be economical. They should not be very high or long or liable to flank attacks of the river during floods. They should be free from obstacles such as hills, frequent drainage crossings, built up areas, sacred areas as grave yards, or trouble some land acquisition etc.

7. The site should be at reasonable proximity to a direct alignment of the road to be connected.

8. There should be no sharp curves in the approaches.

9. Absence of costly river training works, where they are unavoidable they should be executed in dry as far as possible.

10. Avoidance of excessive under water construction work.

11. If it is un-avoidable, necessity for the approaches of the bridge to cross the spill zone of a river, they  should (while processing through the spill zone towards the river), face down stream and not up stream. Facing up stream will cause heading up, pocket formation, and danger to the approaches.