Engineers have been aware
 Скачать 23.55 Kb.
|
|
FOUNDATIONS Why does the Learning Tower of Pisa lean? The answer is that its foundations were not soundly laid. From the earliest times, architects and engineers have been aware of the problems involved in laying a building’s foundations. But they have not always realized what extent the earth can be pressed down by the weight of a building. Too little allowance has sometimes been made for the possibility of a heavy structure’s sinking unevenly. (Though the Leaning Tower is 14 feet out of the perpendicular, it has never toppled. As the building began to lean over, the builders altered the design of the upper stories to balance it. At the same time as one side of it sank into the ground, the earth beneath was compressed until it became dense enough to prevent further movement.) The foundation supports a house. If the earth is stable, laying the foundations of small buildings possess few problems. But in a tall modern structure the load may be very heavy indeed. That’s why the foundation engineer has an extremely important job to do. To begin with, he must have a thorough understanding of soil mechanics, which entails a scientific study of the ground to see what load it can bear without dangerous movement. First construction workers begin excavating, or digging holes or trenches for the footings, the lowest part of the foundation. Trial pits are dug, or holes are bored, in order to collect undisturbed samples of earth from various depths. By examining these, the engineer can forecast the probable shifts in the earth during and after building, according to the sort of foundation he designs. Thus he comes to the most important decision of all in the building’s construction: he decides whether the earth is of the type that can best support each column on a separate solid block, or whether he must aim at lightness and, as it were, float the building on hollow foundations. The footings support each wall load. They are made by pouring concrete into wood or steel forms that workers place below the frost line or the depth to which the ground freezes. This is done so that the footings will not freeze and shift. Footings usually extend from 1 to 6 feet (30 to 180 centimeters) beneath ground level. Builders generally use concrete or concrete block for the house’s foundation. The foundation may extend from 8 inches to 3 feet (20 to 91 centimeters) above the ground. If firm ground has been found only at great depth, the foundation engineer may use piles. These are solid shafts made either by driving reinforced, precast concrete deep into the ground, or by boring holes in the earth and pouring in the concrete. Each pile supports its load in one or both of two ways. It may serve as a column with its foot driven into solid earth or rock or it may stand firm because friction along its sides grips the column and prevents it from sinking. The area within the foundation below the first story is the basement. Basements add to the cost of building a house, but they provide extra room. In other words, when it is a question of floating a building, the foundations take the form of a vast, hollow concrete box. This box is divided into separate chambers for the home’s heating unit, ventilating plants and laundry equipment, and for storage space for the building. Some basements also have a recreation room. Only about 40 per cent of the houses, built today, have basements. In many low or damp regions, houses are raised above the ground on concrete piers, or supports. Sometimes a slab foundation is laid directly on the ground, especially if the earth beneath a house is hard. The ground must first be leveled. Workers then spread a filler, usually stone, and cover it with a moistureproof paper. The filler and the paper prevent moisture from coming through the slab that is made by pouring concrete, about 4 inches (10 centimeters) thick, directly on top of the paper. Luckiest of all are those foundation engineers whose buildings stand on hard rock like granite or ironstone. For them neither piles nor flotation need to be used. Фундамент Почему наклоняется Учебная Пизанская башня? Ответ заключается в том, что его основы не были заложены прочно. С самых ранних времен архитекторы и инженеры были осведомлены о проблемах, связанных с закладкой фундамента здания. Но они не всегда осознавали, до какой степени земля может быть придавлена весом здания. Иногда слишком мало учитывается возможность неравномерного погружения тяжелой конструкции. (Хотя Падающая башня находится на расстоянии 14 футов от перпендикуляра, она никогда не падала. Когда здание начало наклоняться, строители изменили дизайн верхних этажей, чтобы уравновесить его. В то же время, когда одна сторона его погрузилась в землю, земля под ним была сжата до тех пор, пока не стала достаточно плотной, чтобы предотвратить дальнейшее движение.) Фундамент поддерживает дом. Если земля устойчива, то с закладкой фундаментов небольших зданий возникает мало проблем. Но в высоком современном сооружении нагрузка может быть действительно очень большой. Вот почему инженеру-фундаменталисту предстоит выполнить чрезвычайно важную работу. Для начала он должен досконально разбираться в механике грунта, что влечет за собой научное изучение грунта, чтобы увидеть, какую нагрузку он может выдержать без опасного перемещения. Сначала строители начинают выемку грунта, или рытье ям или траншей для фундаментов, самой нижней части фундамента. Пробные ямы выкапываются или бурятся отверстия, чтобы собрать нетронутые образцы земли с различных глубин. Изучив их, инженер может спрогнозировать вероятные сдвиги в грунте во время и после строительства, в зависимости от типа фундамента, который он проектирует. Таким образом, он приходит к самому важному решению в строительстве здания: он решает, относится ли земля к типу, который может наилучшим образом поддерживать каждую колонну на отдельном сплошном блоке, или он должен стремиться к легкости и, так сказать, "парить" здание на пустотелом фундаменте. Опоры выдерживают каждую нагрузку на стену. Они изготавливаются путем заливки бетона в деревянные или стальные формы, которые рабочие размещают ниже линии замерзания или глубины, на которую промерзает грунт. Это делается для того, чтобы опоры не замерзали и не смещались. Опоры обычно простираются от 1 до 6 футов (от 30 до 180 сантиметров) ниже уровня земли. Строители обычно используют бетон или бетонный блок для фундамента дома. Фундамент может простираться от 8 дюймов до 3 футов (от 20 до 91 сантиметра) над землей. Если твердый грунт был обнаружен только на большой глубине, инженер-фундаменталист может использовать сваи. Это сплошные шахты, выполненные либо путем забивания армированного сборного бетона глубоко в грунт, либо путем бурения отверстий в земле и заливки бетона. Каждая свая поддерживает свою нагрузку одним или обоими из двух способов. Он может служить колонной, нога которой вбита в твердую землю или скалу, или он может стоять прочно из-за трения по бокам захватывает колонну и предотвращает ее опускание. Область внутри фундамента под первым этажом - это подвал. Подвалы увеличивают стоимость строительства дома, но они обеспечивают дополнительное пространство. Другими словами, когда речь идет о плавучем здании, фундамент принимает форму огромной пустотелой бетонной коробки. Этот бокс разделен на отдельные камеры для отопительного блока дома, вентиляционных установок и оборудования для стирки белья, а также для складских помещений в здании. В некоторых подвалах также есть комната отдыха. Только около 40 процентов домов, построенных сегодня, имеют подвалы. Во многих низменных или влажных регионах дома поднимаются над землей на бетонных опорах. Иногда плитный фундамент укладывают прямо на землю, особенно если земля под домом твердая. Сначала необходимо выровнять грунт. Затем рабочие насыпают наполнитель, обычно камень, и покрывают его влагостойкой бумагой. Наполнитель и бумага предотвращают попадание влаги через плиту, которая изготавливается путем заливки бетона толщиной около 4 дюймов (10 сантиметров) непосредственно поверх бумаги. Больше всего повезло тем инженерам-фундаменталистам, чьи здания стоят на твердых породах, таких как гранит или железняк. Для них не нужно использовать ни сваи, ни флотацию . INTERIOR CONSTRUCTION OF A HOUSE Interior construction of a house includes: floors, walls, windows, and doors. Floors have two layers. The lower layer lies at an angle across the floor joists. The upper, finished layer is made from tongue and groove boards. One side of each board has a tongue, or lip, and the other side has a groove or slot. The tongue of one board fits snugly into the groove of another board. Carpenters drive nails through the groove side so that the nail heads can not be seen on the finished floor. Most finished floors are made of hardwoods, such as maple or oak, which have been finely sanded and later sealed with wood filler. The wood may then be finished with wax, shellac, varnish, or plastic. Other floors have such coverings as linoleum or rubber, vinyl or asphalt tile. Walls. Rooms are made by building inside walls after the outside walls have been attached to the foundation. Inside walls, also called partitions, are really small-sized frames like the outside walls. They have studs and must be supported by plates, joists and girders. If plaster is to be applied, the interior walls must first be covered with lath, or strips of wood, metal, or plasterboard. The lath is set horizontally about 3 inches (8 centimeters) apart. Wallboard, plasterboard, or plywood may be used in place of plaster. Windows. Most parts of a window come from a lumber mill, already cut in the proper sizes. Carpenters leave space in the frame for windows and window pulleys, weights and sashes. Window sashes are made of wood or metal, usually either aluminium or lightweight steel. Doors. Both doors and door frames may usually be bought ready-made. Carpenters attach the doors high enough to swing over rugs or carpets. A threshold fills in the space under an outside door. Electricity. Electrical wiring provides lighting and furnishes outlets for lamps, washing machines, and other appliances. In some houses, electricity also provides heat. Before construction starts, the builder determines the location and type of wiring. Wires vary in size, depending on the equipment in the house and how far the current must travel. Standard wiring is designed for 110 volt current. But builders often specify heavy-duty, 220-volt wiring if large electrical appliances, such as a stove and a water heater, or an air conditioning system are installed. Electricians install wiring while carpenters build the frame. Wiring is done in a series of circuits. Each set of wires has several outlets. Electricians often place the wiring for a furnace on a separate circuit. This keeps the furnace running in ease if another circuit breaks down. Wires become hot and can cause fires if they are overloaded, so electricians install a fuse for each electrical. A fuse box usually holds all the fuses. If too much current passes through a circuit, the wire in the fuse melts or blows. Electricians often install another protective device called a circuit breaker, instead of a fuse box. If the circuit becomes overloaded, the circuit breaker automatically cuts off the current. THE LAST STEPS IN FINISHING A HOUSE Plumbing. During construction, plumbers install the pipes that will supply gas and water, and carry away waste. They install bathroom fixtures and sinks just before other workers add the finishing touches to the house. Plumbers also install traps to keep out sewages. The trap used for bathroom washbasins, for example a P-shaped pipe, locates directly below the drain. Water settles in the lower part of the pipe and prevents sewages from backing tip and leaking into the room. To function properly, traps must have outside ventilation of the air. A cast-iron waste disposal pipe runs from inside the house to about 5 feet (1,5 meters) outside, where it connects with a pipe of another material, usually clay. This pipe connects home-disposal pipe with the sewerage system of the city. In areas without a city sewerage system, a septic tank near the house holds sewage until it dissolves. Water from the sewage flows through pipes into the ground. The sludge, remaining in the tank, must be removed at intervals. Insulation reduces the amount of heat or cold that passes through walls, floors, and ceilings of a house. When the air around the house is warmer or colder than the air inside, heat passes from the warm air to the cold air. This means that in winter the heat will pass to the outside, and the house will become cold. In summer the heat outside passes into the house. Insulation fills the air spaces in walls, floors and ceilings and creates dead-air space. This helps to prevent heat from passing through. Insulation can save fuel costs in heating a house. Insulation is made from many materials, including cellulose, rock wool, a glassy lava called perlite, gypsum, certain plastics, fiberglass, and a flaky mineral called vermiculite. Insulation comes as blankets, boards, paper and sheathing. It is also available in a loose, crumb like form. The type of insulation used depends on the climate and on whether it insulates floors, ceilings or walls. Heating and air conditioning. Most houses have central heating systems. One furnace or heating unit, supplies heat for the entire house. Such houses are heated by warm air, steam, or hot water. In hot-air heating a fan, connected to the furnace, blows warm air through pipes into the rooms. In steam or hot-water heating the steam or hot water passes through radiators that stand throughout the house. In radiant heating, hot-water pipes run under the floors or in the ceilings or walls. Air-conditioning units may be used to cool and heat houses. An air conditioner takes warm air from the house, cools it, removes moisture, and recirculates cool air. It also may warm cold air, add moisture and recirculate warm air. Interior decoration. In a new house, builders usually paints the rooms and finish the floors as a part of the contract with the homeowner. The owner generally selects, buys and arranges the furnishings. But sometimes the owner hires a professional interior decorator to do this job. Landscaping is the last step in building a house. Most builders try to keep the natural outline of the land and to preserve different sorts of trees which grow in this place. |