Реферат The system of heating
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| Besides masonry, a brick work, any engineer must know about heating and ventilation. They are two branches of engineering which are very closely connected. Both they are treated(1) as a dual subject. Heating is to prevent(2) too rapid loss of heat from the body. The rate of heat lost from the body is controlled. Some old concepts of heating have been gradually(3) changed since engineers obtained more precise knowledge about how the body loses heat. Insufficient(4) attention was paid formerly to loss by radiation, which is the transmission of energy in the form of waves from a body to surrounding bodies at a temperature. The human being also loses heat by conduction (through his clothes) and convection. |
| . The most widely used system of heating is the central heating. There are two most common(5) systems of heating: hot water and steam. There the fuel is burned in one place, from which steam, hot water or warm air is distributed to adjacent and remote spaces to be heated. |
| Both systems are widely used nowadays. A hot-water system consists of the boilers and a system of pipes connected to radiators suitably located in the rooms. The steel or copper pipes give hot water to radiators or convectors which give up their heat to the rooms. Then cooled water is returned to the boiler for reheating. As for steam systems, steam is usually generated. The steam is led to the radiators through or by means of steel or copper pipes. The steam gives up its heat to the radiators and the radiators to the room. After this cooling of the steam condenses(6) to water. The condensate is returned to the boiler by gravity or by a pump. The air valve on each radiator is necessary for air to escape. Otherwise(7) it would prevent(8) steam from entering the radiator. |
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| But, to do comfortable atmosphere is to use heating and ventilation together. Heating and ventilation are concerned with providing(9) a required atmospheric environment within a space to produce a desired temperature for comfort. Nowadays air-conditioning is closely related to both heating and ventilation. |
| We have mentioned about building materials as one of the components of building. It is high time to tell about them. It is important for an engineer to know that all building materials are used in two basic ways. In the first way they are used to support the loads on a building and in the second way they are used to divide the space in a building. But it is more important to realize that building components are made from building materials. |
| 1. The first type of a construction is made of building materials such as a brick, a stone or concrete. They are called blocks. The blocks arc put together to form solid(10) walls. These materials are heavy. They can support the structural loads because they have the property of high compressive strength. At the same time the walls made up of blocks support the building and divide the space in the building. |
| 2. The second type of a construction is made of sheet materials. Timber, concrete and some plastics can be made into large rigid sheets and fixed together to form a building. Such kind of buildings is lighter and faster to construct than a building made up of blocks. |
| 3. The third type of a construction is made of rod materials. They can be used for structural support but not for dividing spaces. There timber, steel and concrete can be formed into rods. Usually rod materials are used as columns because of high tensile(11) and compressive strength. On the other hand, they can be fixed together to form framed structures. The spaces between the rods can be filled with light sheet materials. |
| Building materials are very important in the construction. But it is more important for any designer to select and adapt such building materials of construction that will give the most effective result by the most economical means. In this choice of materials for any work of constructions many factors must be considered(12) by the civil engineer. These factors include availability(13), cost, physical properties of materials and others. |
| Practically, all buildings materials have their advantages and disadvantages. That's why some materials are used most widely in building construction for the purpose of binding together masonry units. Among them are lime, gypsum and cement. Last material forms very important elements in all masonry structures, such as stone, a brick. Since the time of its introduction a gradual(3) improvement of Portland cement quality has led to the elaboration of rapid hardening Portland cement. |
| So, cement is the most important component of concrete. Concrete is even less uniform than many other materials. Concrete may be considered(12) an artificial conglomerate of "crushed stone, gravel or similar inert(14) material with a mortar". |
| One of the building materials used in a construction is a brick. The production of a brick was industrialized in the 19th century. Earlier it was a process of hand-molding. Later it was superseded by «pressed» bricks. It was a mass production by a mechanical extrusion(15) process. In this way clay was squeezed(16) through a rectangular(17) die as a continuous column and sliced to size by a wire cutter(18). Bricks were moved slowly on a conveyor belt. New methods considerably reduced(19) the cost of a brick. That's why it became one of the constituent(20) building materials of the age. |
| Rapid development of timber technology was in the I9th century in It provided other necessary ingredient — a balloon frame. That made possible a major innovation in building construction. The first example was a warehouse erected in |
| Among the oldest and newest of structural materials are composite materials. It was discovered many years ago that two or more materials could be used together as one. Later it was proved(22) that such a combination often behaved better than each material alone. Following this principle, clay and straw were combined to make bricks. For centuries composite materials remained virtually untapped. (23) Only then monolithic materials, such as iron, copper were served for needs of an advancing technology. Recently (24) it was a development of technology with coming of reinforced concrete, linoleum and plywood panels. |
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| All cultures have their own traditions. That's why it is important to know about them. Of cause, architecture has its own history. There are a lot of different kinds of architectural styles, describing some features of every country. For example, red brick buildings of old |
| Let's tell some words about a basic fast construction for buildings. It is a metal skeleton. There metal vertical racks and horizontal crossbar with the help bolt connections gather(31) in cross-section frames. The cross-section frames are a system of extensions(32) or communications, giving to design settlement durability fastens. (33) Then it is established(34) roofing, wall runs(35), frames under windows, doors. Any engineer may say that a bearing(36) skeleton is ready. Further it is possible to use any facing. |
| It can be Ferro-concrete, bricklaying, special panels such as "sandwich", any combinations of the specified designs. It is necessary to tell some words about panels such as "sandwich". Every panel consists of two sheets of the zinced iron between which a special heater is placed. The design has no internal skeleton. It is very important for a future skilled engineer to remember about a distinctive(37) feature such as "fast". It is a high degree of a factory's readiness(38) to complete the building. All details, delivered to a building site, are made at a factory with their obligatory test characteristics(39) of strong. On a building site all elements of a design are gathered(40) with the help bolt connections. |
| The scope of fast metallic construction is very wide. For example, metallic construction is not used at construction of buildings in which nuclear reactors will place, or bank storehouses. There walls' and roofing designs should possess raised isolation properties. It is not accepted to use them. Practically, fast metallic constructions are used at the construction of any industrial targets, warehouses, sports complexes. Recently fast construction designs are used in the market. This process does metallic construction attractive in the field of trading constructions. |
| Every construction has its own advantages and disadvantages. Advantages of a fast metallic construction are obvious. A cost of a building from a metallic construction is 30-40 % less, than on construction of a similar building, using traditional materials. Naturally, the given statement(41) is correct only under condition of the certain identity of quality of external and internal furnishing(42). For example, the building constructed from the cheapest brick without additional external furnishing, will be cheaper than a construction from a fast metallic construction with a facade trimmed with dark glass. The essential economy, while using a metallic construction, is reached to decrease(43) in expenses of a zero cycle approximately on 50 %. Today a fast metallic construction is a leader among all building designs, first of all, because of its low price. |
| Various materials are used as a solution for fastening(44). It was so a long ago. Sometimes in Mesopotamia (modern But the limy solution was easily washed away by a rain. Subsequently Greeks and Romans took more durable cement mortal on arms -a mix to exhaust, sand and Volcanic ashes. Later Romans began to add to it gravel for reception of concrete. Greeks continued building of integral blocks of a stone or marble. One more major landmark became manufacturing bricks in the furnace for roasting(45) at high temperatures. So it was received stronger and more durable material. But Romans used only thin layers of these materials for facing concrete designs. Besides dwellings, builders could erect majestic palaces, temples and monuments. They also decorated with their decorative stone lying. (46) |
| Many things are made by metal tools. Metal tools allow cutting, squaring and polishing(47) a stone. Metal tools such as an axe, a saw, builders used many years ago. Also they had an opportunity to use available materials more widely. Now they could cut the big trees and split them and bars. |
| Many new materials are familiar to us over centuries. We are pretty well acquainted(48) with the advantages and disadvantages of wood. We know that glass is transparent, but in some ways it is rather brittle(49). Glass has the advantages of cheapness, rigidity and chemical inertness. We are aware(50) that most metals can stand severe handling(51), but some of them rust. |
| But such materials as plastic materials are not found in nature. Some years ago plastics were little more(52) than laboratory curiosities. Today plastics are conceived(53) in the laboratory of the chemical plant. But plastic is formed by extrusion or injection molding(54) under very high pressure. It can be molded into any desired shape. Organic plastics are divided into two general groups: thermosetting and thermoplastic. The thermosetting group becomes rigid through a chemical change that occurs when heat is applied. These plastics cannot be remolded. |
| The thermoplastic group remains soft at high temperatures and must be cooled before becoming rigid. This group is not used generally as a structural material. |
| Plastics are rapidly becoming important construction materials because of their great variety, strength, durability and lightness. The high strength to weight ratio of some plastics offers big field in the coming age of space travels and rockets. Plastics are light. The same benefits of light weight coupled with good strength and absence of corrosion offer tremendous potential as alternatives to traditional building materials. A given volume of polythene weights less than one-eighth of an equal volume of iron and less then half of the same volume of aluminum. The following characteristics of plastics are usually shared by all plastics: lightweight, corrosion resistance, electrical and thermal insulation, ease of fabrication, ease of coloring and economy of production. |
