Краткое изложение текста "The Design of Concrete Pavement" с элементами аннотирования и реферирования
The design of Concrete Pavement
The performance of a concrete pavement for traffic riding purposes depends not only upon the property of materials but also on the underlying sub-grade or the base course. The design of a concrete pavement must involve all physical properties of concrete. Concrete withstands high compression but it is low in tension (flexure). Like wood, it expands on wetting and shrinks while drying. With temperature, like other materials, it decreases or increases in length. Under some conditions its volume increases with age. A concrete pavement when subjected to variations of daily temperature and moisture between the top and the bottom of the slab will have a tendency to warp and curl.
The following conclusions have been generally established after a series of theoretical approaches and practical results in concrete pavement design:
1.Cracking due to flexure is almost inevitable in a concrete slab of any great length.
2.For constant loads on slabs of reasonable length, load and total stress decrease as slab thickness increases, that is to say, if the safe working stress were to remain the same, the slab thickness must increase as wheel loads increase.
Reinforcement. The provision of reinforcement in a concrete pavement is designed to hold cracks that develop due to flexural stresses as close as possible, so that they may not develop into a major defect. It must be remembered that reinforcement is not used either to increase the load bearing capacity or for complete prevention of cracking. Reinforcement may be used: 1. To prevent fracture surface from widening and to tie all parts of the slab together. 2. Where there is a possibility for the sub-grade to become weak and non-uniform in bearing, so that the induced cracks may not get widened and exposed to action of dirt and water. If additional load bearing capacity is required this can be easily achieved by thickening the pavement.
The United Kingdom is made up of four countries: England, Wales, Scotland and Northern Ireland. Their capitals are London, Cardiff, Edinburgh and Belfast respectively. The population of the country is over 57 million people; about 80 per cent of them live in cities and towns.
Many centuries ago the islands were inhabited by Celts. Their tribes were developing into kingdoms when Julius Caesar invaded Britain in 55 B.C. The Roman invasion began in AD 43. The Romans withdrew in 407. The tribes of Angles and Saxons crossed the Channel and overran all England except Cornwall and Wales. Christianity was introduced in the 6th century by missionaries from Rome.
The surface of the British Isles varies very much. The north of Scotland is mountainous and is called the Highlands, while the south, which has beautiful valleys and plains, is called the Lowlands. The north and the west of England are mountainous, but all the rest — east, centre and south-east — is a vast plain. The mountains are not very high. Ben Nevis in Scotland is the highest mountain (1343 m).
There are a lot of rivers in Great Britain, but they are not very long. The Severn is the longest river, while the Thames is the deepest and the most important one.
The mountains, the Atlantic Ocean and the warm waters of Gulf Stream influence the climate of the British Isles. It is mild the whole year round. But the climate is not the same in all parts of England. The western part of England is warmer than the past and it also has more rain. There is much humidity in the air of England. It is well known as a foggy country.
The United Kingdom is a monarchy. The Queen is the official head of state. In practice the country is ruled by an elected parliament. The British Parliament has two chambers: the House of Lords and the House of Commons. There are three main political parties: the Labour, the Conservative and the Liberal. In 1997 a general election was held. The Labour party achieved a majority in the House of Commons, and the leader of the party Tony Blair was appointed Prime Minister by the Queen.
The United Kingdom is a highly developed industrial country. It is known as one of the world's largest producers and exporters of machinery, electronics, textile, aircraft and navigation equipment. One of the main industries of the country is shipbuilding.
The United Kingdom of Great Britain and Northern Ireland is situated on the British Isles. The British Isles consist of two large islands, Great Britain and Ireland, and above five thousand small islands. Their total area is over 315 000 square kilometers. The United Kingdom is made up of four countries: England, Scotland, Wales and Northern Ireland. Their capitals are London, Edinburgh, Cardiff and Belfast respectively.
The British isles are separated from the European continent by the North Sea and the English Channel. The western coast of Great Britain is washed by the Atlantic Ocean and the Irish Sea. The surface of the British Isles varies very much. The north of Scotland is mountainous and is called Highlands, while the south, which has beautiful valleys and plains, is called Lowlands. The north and west of England are mountainous, but all the rest - east, center and southeast - is a vast plain. Mountains are not very high. Ben Nevis is the highest mountain. (1343 m.)
There are a lot of rivers in GB, but they are not very long. The Severn is the longest river, while the Thames is the deepest and the most important one.