Oral+Presentation+(Arch)

**__Arch.__**  An Arch is a structure that spans a space while supporting weight. They appeared as early as the 2nd millennium BC in Mesopotamian brick architecture and their systematic use started with the Ancient Romans who were the first to apply the technique to a wide range of structures.

** History. ** True arches, as opposed to corbel arches, were known by a number of civilizations in the Ancient Near East, the Levant, and Mexico, but their use was infrequent and mostly confined to underground structures such as drains where the problem of lateral thrust is greatly diminished.

The ancient Romans learned the arch from the Greeks and Etruscans, refined it and were the first builders to tap its full potential for above ground buildings.



 Throughout the Roman empire, their engineers erected arch structures such as bridges, aqueducts, and gates. They also introduced the triumphal arch as a military monument. Vaults began to be used for roofing large interior spaces such as halls and temples, a function which was also assumed by domed structures from the 1st century BC onwards.



**Principal types of arches.**
 *  The semicircular arch was followed in Europe by the pointed Gothic arch or ogive whose centreline more closely followed the forces of compression and which was therefore stronger. It can be flattened to make an elliptical arch.




 *  The horseshoe arch is based on the semicircular arch, but its lower ends are extended further round the circle until they start to converge.




 *  The parabolic and catenary arches are now known to be the theoretically strongest forms. They were introduced in construction by the Spanish architect AntoniGaudí. Also, they carry all horizontal thrust to the foundation and so do not need additional elements.








 *  The segmental arch was first built by the Romans who realized that an arch in a bridge did not have to be a semicircle. They were also routinely used in house construction.

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