Bridges 2 Essay, Research Paper
Beam Bridge
Beam bridges are the simplest form of bridge. They have developed from a log
across a river to the large box girder bridges that you see today. In between there have
been many different types of beam bridge.
A Clam Bridge
This is another early form of a beam bridge. it consists of a single slab of stone supported
at each end stretching from bank to bank, making a single span.
A Clapper Bridge
This is a bridge that consists of a number of stone slabs that provide a multi-span
crossing. Each span is simply supported at each end.
All bridges are concerned with providing the necessary stiffness to prevent
bending and twisting when a load is applied. All beams are good at this ( infact any
member that resists a load is called a beam). The load applied to the bridge is transferred
to the supports where the load act downwards.
Archbridges have been in use for thousands of years. The Romans made much use
of arches and many of their aqueducts and viaducts still stand today. They discovered that
small wedge shaped stones can, when placed to form a semicircle, resist large weights
from above. Originally they were built from stone, and later brick, they are now
commonly built from reinforced concrete or steel. The newer materials allow a much
longer and lower span to be built. Arches carry their load by transferring the load to the
supports at either side. These supports must be rigidly fixed in the ground to stop them
spreading apart.
This diagram shows you the name for each part of an arch bridge. The most
important part is the brick in the middle of the arch called a keystone.
A cantilever projects outwards and is supported at one end only as shown.
Cantilever bridges usually use a pair of cantilevers, often to support a beam set between
the two cantievers. Many modern bridges over motorways use cantilevers in pairs. They
have a cantilever coming out from each side and a short beam between them.
Suspension bridges originated as rope and wood structures in various parts of the
world. Modern bridges use a bow sectioned roadway suspended from cables made from
extremely strong high tensile steel wires. The main cables, supported by the twin towers,
have to be securely anchored to the ground on either side of the bridge. Using suspension
bridges have an advantage that they are cheap and give long clear spans, making them the
most economical method of bridging large spans.