Bridges help people and vehicles cross over obstacles like bodies of water, railways, and roads. The earliest bridges were made of wood, but now bridges are often constructed of stronger materials like steel and concrete. There are four main types of bridges: beam bridges which consist of a horizontal beam supported at each end; cantilever bridges which extend outward from each end and meet in the middle; arch bridges which are curved like an arch; and suspension bridges where the roadway is suspended from cables running between two towers.

1. BRIDGES TO CROSS
Bridges are structures that
helps us to cross over a
water body ,a railway track or
a road.

2. What are bridges made of ?
•The earliest bridges were made up of wooden logs or
planks and sometimes stones.
•Even now, in some parts bridges over streams and
small rivers are made of locally available material like
bamboo and wood.
• later strong materials like iron, steel and other
stronger materials were used which could take the
load of heavy traffic and force of winds.
•Bridges made by the masons from cement ,brick and
stone became common.
•Modern bridges are built mainly from steel or
concrete .
•Steel is the strongest bridge building material but it
usually needs to be painted and requires constant
maintenance to prevent wear and tear.

3. TYPES OF BRIDGES
There are mainly four different kinds of bridges:
Beam bridges
Cantilever bridges
Arch bridges
Suspension bridges

4. BEAM BRIDGES
•Beam bridge is the simplest of many bridge types in terms
of its structure.
•It consists of a horizontal beam that is supported bat each
end by vertical pillars .
•A beam is a long thick piece of wood, metal or concrete
used in construction.
•The log bridges were the earliest examples of beam
bridges.
•Now beam bridges are also made of steel beams or
reinforced concrete.
•Pedestrian bridges and highway overpasses and flyovers
are often beam bridges.
•For example ,the lake Pontachartrain Causeway in the
USA is the longest beam bridge over water in the world.

5. CANTILEVER BRIDGE:
•A cantilever bridge is a bridge which is supported
only by beams at the two opposite ends.
•The beams are called Cantilevers.
•The bridge extends in opposite directions from both
ends and meets at the centre.
•The bridge over the Bhramaputra Rivet,the
Naranarayan Setu ,is a cantilever bridge.

6. ARCH BRIDGE:
•An Arch bridge is one of the oldest types of bridges.
•It is curved in the shape of an arch.
•The arch is supported at either end by structures called
abutments.
•These supports carry the load of the arch and prevent it from
collapsing.
•Arch bridges were originally built of dtone or brick but are mostly
built of reinforced concrete or steel these days.
•The Chaotianmen bridge ,is a road –rail bridge over the Yangtze
River in China. Its main arch is the longest in the world.

7. SUSPENSION BRIDGE:
•A suspension bridge has cables or ropes strung across the river and
the roadway is suspended from these cables.
•The earlier and simpler suspension bridges ,followed a shallow
downward arc and were not suited to modern road or rail traffic.
•The Lakshman Jhoola near Rishikesh in Uttar Pradesh is one such
example.
•In modern suspension bridges ,the cables are strung through two tall
towers which take the weight of the roadway.
•These bridges are capable of carrying vehicles and light trail.
•The Golden Gate bridge is suspension bridge spanning the Golden
Gate ,the opening of the San Francisco Bay into the pacific ocean.

8. PONTOON BRIDGE:
•During floods and calamities the army builds pontoon bridges
using boats.
•A number of boats are tied together and a pathway laid over
them for people to cross.
•Some of these are quite strong and remain in use for long
periods of time.